1,720,980 research outputs found
Inverse modeling of unsaturated flow using clusters of soil texture and pedotransfer functions
Full text linkCharacterization of heterogeneous soil hydraulic parameters of deep vadose zones is often difficult and expensive, making it necessary to rely on other sources of information. Pedotransfer functions (PTFs) based on soil texture data constitute a simple alternative to inverse hydraulic parameter estimation, but their accuracy is often modest. Inverse modeling entails a compromise between detailed description of subsurface heterogeneity and the need to restrict the number of parameters. We propose two methods of parameterizing vadose zone hydraulic properties using a combination of k-means clustering of kriged soil texture data, PTFs, and model inversion. One approach entails homogeneous and the other heterogeneous clusters. Clusters may include subdomains of the computational grid that need not be contiguous in space. The first approach homogenizes within-cluster variability into initial hydraulic parameter estimates that are subsequently optimized by inversion. The second approach maintains heterogeneity through multiplication of each spatially varying initial hydraulic parameter by a scale factor, estimated a posteriori through inversion. This allows preserving heterogeneity without introducing a large number of adjustable parameters. We use each approach to simulate a 95 day infiltration experiment in unsaturated layered sediments at a semiarid site near Phoenix, Arizona, over an area of 50 × 50 m2 down to a depth of 14.5 m. Results show that both clustering approaches improve simulated moisture contents considerably in comparison to those based solely on PTF estimates. Our calibrated models are validated against data from a subsequent 295 day infiltration experiment at the site
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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Transpiration, Growth And Survival Of Native Riparian And Introduced Saltcedar Trees In Mixed Stands On The San Pedro River, U.S.A.
No full textWestern riparian zones have undergone significant landscape changes over the past several decades, with introduced saltcedar (Tamarix spp.) as a crucial component of this transformation. Saltcedar, now a dominating presence along many western rivers, due to its high tolerance to drought, salinity and stress, is considered to be a high-water-use plant that can desiccate disturbed river systems. Where native and saltcedar plant communities occur together, it is important to understand water use patterns and the physiological responses of each species to environmental stress factors, as a way to project an eventual course of succession processes and management options at a given site. Stress and disturbance in the form of reduced stream flows and land use changes may influence these interactions. Understanding the conditions that allow for saltcedar dominance is critical in determining riparian water budgets, and developing effective management strategies. Sap flux sensors were used to measure the physiological response of co-occurring communities of saltcedar and native trees to these environmental stress factors during the pre-monsoon period in early summer, a time of maximum stress for riparian vegetation. The results suggest that native trees are still competitive with salt cedar so that a mixed plant community is likely to continue on the San Pedro River on the condition that current groundwater levels and river flows are maintained. If base flows and depth to groundwater continue to decline, this competitive balance between saltcedar and native trees likely could change
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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Drought Monitoring in the Southwestern United States: Analysis of Seasonal Precipitation, Multiscalar Indices, and Soil Water
No full textDrought is a complex, natural hazard that can cause widespread socioeconomic and environmental impacts. Drought can be defined as a water deficit that arises compared to normal conditions and lasts long enough to cause a lasting hydrological imbalance; however, what constitutes normal conditions varies based on the local climate regime and water source being studied. It is therefore that drought can be subjective to the observer and accounting for the correct environmental drivers is important to accurately assess drought impacts. In water-limited ecosystems like the Southwestern United States, hereby referred to as the Southwest, monitoring drought conditions presents unique challenges as annual potential evapotranspiration is significantly greater than precipitation. Primary production of Southwestern vegetation is adapted to the timing and magnitude of soil water recharge from seasonal precipitation. Variations in precipitation timing and magnitude can thus lead to lasting drought impacts and therefore tracking soil water at different depths is key for understanding overall ecosystem health.
Studies have monitored soil water availability by placing Time Domain Reflectometry (TDR) probes at different depths within a soil profile. However, varying measurements between TDR probes due to differences in soil properties, calibration complications, and maintenance issues have led to the lack of long-term, reliable soil water datasets. This has restricted drought analysis using soil water data to a more local scale. As an alternative approach, land managers and decisions makers use meteorological drought indices as proxies for soil water availability. Meteorological drought indices are numerical timeseries that convey the frequency and magnitude of meteorological indicators, such as precipitation and temperature. Examples of meteorological drought indices are the Standardized Precipitation Index (SPI) and Standardized Precipitation-Evapotranspiration Index (SPEI), which use monthly total precipitation and water balance values, respectively, to communicate drought conditions. A key feature of the SPI and SPEI is the ability to be calculated at any monthly timescale length (‘multiscalar’), allowing for drought conditions of different water sources, such as shallow soil water, to be evaluated. Furthermore, the SPI and SPEI require minimal data inputs and are simple to calculate. It is therefore that the SPI and SPEI are commonly used by land managers for drought monitoring and decision making.
Using SPI and SPEI timescales to estimate soil water in the semi-arid Southwest can be complicated as not all falling precipitation can be assumed to infiltrate into a soil profile. This is due to low intensity precipitation events being captured by tree canopy interception or evaporation and increased runoff during high intensity events. These issues complicate objectively identifying the index and timescale length that best represents soil water availability at different depths, leaving a significant gap between applying meteorological drought index information to land management action for the Southwest. Furthermore, the lack on in-situ soil water datasets prevents characterizing the full relationship between index timescale and soil water. Moreover, the lack of soil water datasets limit the study of links between Southwestern climate, intra-annual soil water variability, and soil drought dynamics on a regional scale. This dissertation address these gaps by creating a regional soil water dataset for the Southwestern United States for the purpose of improving drought monitoring and our understanding of drought development in soils.
By coupling sophisticated computer modeling, site-specific soils information, and spatially continuous, high resolution meteorological datasets, this dissertation simulated daily matric potential values from 0-200cm at 240 locations across the Southwest. Through a series of investigative studies central to the Southwest, this dissertation quantified historical drought events in soils (appendix A), defined the relationship between meteorological drought index timescale and soil water depth (Appendix B), and developed a time-varying approach designed to improve multiscalar index approximation of soil water in climates with seasonal precipitation distributions (Appendix C).
The first study (Appendix A) quantified how changes in the timing or magnitude of seasonal precipitation translated to soil drought onset and cessation patterns. Results showed that annual matric potential values followed a location’s seasonal precipitation distribution. Short-term droughts (60 – 270 days) were frequent, and typically resulted from delayed or slowed starts to a locations major rainy season. Long-term droughts (>270 days) were infrequent and occurred only during specific years, requiring anomalous below average precipitation in one or more consecutive rainy seasons to develop. Long-term droughts were more likely to occur in locations with unimodal precipitation distributions (a majority of rain occurring once annually), due to soil water anomalies likely remaining unresolved until the following rainy season. Locations with bimodal precipitation distributions (rainy seasons occurring twice annually) made long-term drought development difficult as consecutive below average rainy seasons were needed.
The second study (Appendix B) defined the relationship between multiscalar index timescale and soil water availability for the Southwest. For all 240 locations, a new matric potential index (MPI) was created at 5cm intervals between 0-200cm and correlated with timescales from 1-24 months for the SPI and SPEI. Results showed the relationship between the highest correlating index timescale at each MPI depth operates roughly on a 1:1 step progression at shallow depths. Further analysis showed that soil type impacts the timescale-depth relationship, with clay loam soils correlating at longer timescales than sandy soils when correlating with the same depth MPI. Additionally, the SPI produced higher correlations and with the MPI compared to the SPEI. Therefore, this studied recommended SPI usage for shallow (<80cm) soil water monitoring on Southwestern drylands, with a general rule that the relationship between timescale and depth scales linearly in a 1:1 progression. However, if land managers have access to local soils information, it should be consulted given the impacts of soil type on the timescale-depth relationship.
Given the importance of seasonal precipitation timing and magnitude for vegetation productivity, the use of a single multiscalar index timescale is unlikely to fully represent intra-annual variability of soil water. The third study (Appendix C) used a novel approach that created a time-varying multiscalar composite index for the SPI and SPEI (‘composites indices’) designed to better approximate seasonal soil water variability in the Southwest. The composite indices were compared with the SPI and SPEI using a traditional single timescale to evaluate improvement in soil water approximation at different depths. Results showed that the timescale-varying approach significantly improved the ability of the SPI and SPEI to approximate soil water over the use of a single timescale. Improvements varied by multiscalar index, depth, and soil type. Land managers can benefit from this approach by understanding general seasonal relationships between timescale length and soil water availability.
Together, this dissertation links Southwestern climatology, intra-annual soil water availability, and drought development in soils by creating a regional soil water dataset with high spatial and temporal resolution. This dissertation’s findings will aid further research efforts into soil drought dynamics and improve drought monitoring in the semi-arid Southwest. As climate change exacerbates stress on water limited ecosystems, fully utilizing available drought monitoring strategies is key for forming strong mitigation and adaptation plans. The author of this dissertation hopes these results will benefit land managers and policymakers during the decision-making process and increase usage of multiscalar meteorological indices, such as the SPI and SPEI, as a viable drought monitoring tool of soil water availability in the Southwestern United States
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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