28,628 research outputs found
"Closing the R&D Gap, Evaluating the Sources of R&D Spending"
No full textBoth spending and tax policies have been implemented in the United States with the goal of stimulating private sector research and development (R&D). Karier questions whether current R&D policy, especially the research and experimentation tax credit, can contribute to closing the gap between nondefense expenditures on R&D in the United States and such expenditures in other countries, such as Japan and Germany. He also explores possible changes to our current R&D policy to make it more effective.
Volcanic ash deposition as a selection mechanism towards woodiness
No full text: The high proportion of woody plant species on oceanic islands has hitherto been explained mainly by gradual adaptation to climatic conditions. Here, we present a novel hypothesis that such woodiness is adaptative to volcanic ash (tephra) deposition. Oceanic islands are subject to frequent eruptions with substantial and widespread ash deposition on evolutionary time scales. We postulate that this selects for woodiness through an increased ability to avoid burial of plant organs by ash, and to re-emerge above the new land surface. We sense-checked using observations of plant occurrences and distributions on La Palma (Canary Islands) in April 2022, 4 months after the end of the eruptions of the Tajogaite volcano (Cumbre Vieja ridge). In contrast to herbs and grasses, most woody plants persisted and were already in full flower in areas with 10+ cm ash deposition. Remarkably, these persisting woody plants were almost exclusively endemics
Testing of Drivers for Plant Species Diversity Along Elevational Gradients on Seven Mountainous Islands in the Subtropics
No full textAimsGeographic variation in species richness along elevational and latitudinal gradients may be controlled by energy, water, and productivity; however, spatial factors such as area and geometric constraints may also contribute. We use large mountainous oceanic islands, which exhibit considerable range in all proposed driver variables, to test established plant diversity models, such as the mid-domain effect (MDE), actual evapotranspiration (AET, energy), water-energy dynamics (WED: precipitation + potential evapotranspiration), and net primary production (NPP). LocationWe used published data comprising complete floras with elevation-specific occurrence information for seven mountainous oceanic islands (> 2000 m asl) in tropical and subtropical zones. MethodsFor each of the seven islands, plant richness was estimated within each 100 m elevation band (interpolated from maximum and minimum elevation). We used generalized linear models to evaluate the effects of area, MDE, AET, NPP (MODIS), and WED on each island and all islands simultaneously. The general WED model used in this study is a two-term model that includes a second-order polynomial function of PET and a linear function of precipitation. We use AIC and the proportion of explained deviance to identify the best model for explaining variation in plant richness along elevational gradients on mountainous islands. ResultsWe found remarkably consistent patterns in which AET and MDE failed to offer a good explanation for species richness. WED was the best model when all islands were analyzed simultaneously; however, analyses on separate islands revealed that the precipitation term was not significant or negatively related to richness on five of the seven islands. The second-best model was NPP, whereas the best single predictor of richness was the polynomial expression of PET. The spatial variables, area, and the autocorrelated masl were strongly correlated with the residuals of the weak models. ConclusionsBased on these observations, WED and NPP are superior in explaining richness on mountainous islands, whereas MDE and AET have low explanatory power. Precipitation has a negative correlation with species richness in five out of seven islands
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
Dispelling the Myths Behind First-author Citation Counts
No full textWe 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
Impacts of forest fire on understory species diversity in canary pine ecosystems on the island of la palma
No full textForest fires are drivers of spatial patterns and temporal dynamics of vegetation and biodiversity. On the Canary Islands, large areas of pine forest exist, dominated by the endemic Canary Island pine, Pinus canariensis C. Sm. These mostly natural forests experience wildfires frequently. P. canariensis is well-adapted to such impacts and has the ability to re-sprout from both stems and branches. In recent decades, however, anthropogenically caused fires have increased, and climate change further enhances the likelihood of large forest fires. Through its dense, long needles, P. canariensis promotes cloud precipitation, which is an important ecosystem service for the freshwater supply of islands such as La Palma. Thus, it is important to understand the regeneration and vegetation dynamics of these ecosystems after fire. Here, we investigated species diversity patterns in the understory vegetation of P. canariensis forests after the large 2016 fire on the southern slopes of La Palma. We analyzed the effect of fire intensity, derived from Sentinel-2 NDVI differences, and of environmental variables, on species richness (alpha diversity) and compositional dissimilarity (beta diversity). We used redundancy analysis (dbRDA), Bray–Curtis dissimilarity, and variance partitioning for this analysis. Fire intensity accounted for a relatively small proportion of variation in alpha and beta diversity, while elevation was the most important predictor. Our results also reveal the important role of the endemic Lotus campylocladus ssp. hillebrandii (Christ) Sandral & D.D.Sokoloff for understory diversity after fire. Its dominance likely reduces the ability of other species to establish by taking up nutrients and water and by shading the ground. The mid-to long-term effects are unclear since Lotus is an important nitrogen fixer in P. canariensis forests and can reduce post-fire soil erosion on steep slopes
Co-occurrence frequency in vegetation patches decreases towards the harsh edge along an arid volcanic elevational gradienta
No full textPositive plant-plant interactions are thought to drive vegetation patterns in harsh environments, such as semi-arid areas. According to the stress-gradient hypothesis (SGH), the role of positive interactions between species (facilitation) is expected to increase with harshness, predicting associated variation in species composition along environmental gradients. However, the relation between stress and facilitation along environmental gradients is debated. Furthermore, differentiating facilitative interactions from other underlying mechanisms, such as microtopographic heterogeneity, is not trivial. We analysed the spatial cooccurrence relationships of vascular plant species that form patchy vegetation in arid lapilli fields (tephra) from recent volcanic eruptions on La Palma, Canary Islands. We assume a harshness gradient negatively correlated with elevation because of more arid conditions at lower elevations where water availability is considered the most limiting resource. Based on the SGH we expect a greater degree of co-occurrence at lower elevations, as an outcome of facilitation is plants co-occurring in the same patch. We tested this at both the species and the individual plant level. We analysed the species composition of 1277 shrubby vegetation patches at 64 different sampling points, ranging from the coast to around 700 m a.s.l. Patch morphology and microtopographic heterogeneity variables were also measured, to account for their potential effects on the species composition of patches. We used generalized linear models and generalized mixed-effects models to analyse species richness, number of individuals in patches and percentage of patches with positive co-occurrences, and a pairwise co-occurrence analysis combined with a graphical network analysis to reveal positive links between 13 of the species. We found that the percentage of patches with positive co-occurrences increased at higher elevations, in contrast to the predictions of the SGH, but in accordance with a refined stress-gradient hypothesis for arid sites, in which characteristics of the interacting species are incorporated
Investigating elevational gradients of species richness in a Mediterranean plant hotspot using a published flora
No full textThe Apuan Alps are one of the most peculiar mountain chains in the Mediterranean, being very close to the coastline and reaching an elevation of almost 2000 m. Based on published flora, we investigated the distribution of plant species richness along the whole elevational gradient of this chain considering: (i) native species, (ii) endemic versus alien species; and (iii) functional groups of species based on Raunkiær life forms (RLF). Generalized Linear Models (GLMs) were used to analyse richness patterns along the elevational gradient, and elevational richness models versus the area of the elevational belts were fitted to test the effect of surface area. Our results showed decreasing species richness with increasing elevation. In contrast, endemic species richness increased along the elevational gradient. Alien species were mainly distributed at low elevations, but this result should be taken with caution since we used historical data. Species life forms were not equally distributed along the elevation gradient: chamaephytes and hemicryptophytes were the richest groups at high elevations, while therophytes showed highest species richness at low elevations. Our findings suggest that in the Apuan Alps there is a major elevational gradient in species composition that could reflect plant evolutionary history. Furthermore, we highlight the key role of published floras as a relevant source of biodiversity data
Avatar's 'Development' Predicament
No full textThe globally-acclaimed film looks back to the past from a futuristic standpoint to simulate an archetypal moral tale of developmental inequality. Is that a good thing
Roughness-triggered turbulent boundary layers in Rayleigh-Bénard convection
No full textWe present measurements carried out inside the Barrel of Ilmenau as part of the European EuHIT transnational infrastructure access program. The Barrel of Ilmenau is the worldwide largest experiment to study highly turbulent convection in air. A rectangular cell, with proportions strictly identical to the water cell in Lyon [Salort, et al. PoF 26:015112 (2014)], but six times larger, has been inserted inside the Barrel. The top plate is smooth, and the bottom plate is rough. The roughness are also similar to the one in Lyon, but six times larger. We have obtained velocity fields using PIV near the obstacles, as well as the local heat-flux on the bottom plate. This has allowed us to test and improve our previous interpretation of the roughness-induced heat transfer enhancement mechanisms
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