1,720,995 research outputs found
Recommended from our members
Chapter 6 - Future changes in precipitation distributions over Africa
No full textThe African continent is home to approximately 1.4 billion people, about 18% of the world's population. Monsoon precipitation is critical to African societies, contributing a large proportion of the average annual precipitation. Variations in monsoon precipitation have major impacts on, for example, agriculture, freshwater supply and sanitation, and hydropower generation. Unusually low precipitation can also lead to large and prolonged droughts across Africa, increasing mortality. Future changes in monsoon precipitation, therefore, have important societal implications. In this chapter, we summarize the impact of climate change on future changes in precipitation over Africa and for the end of the 21st century. Climate models show that precipitation is projected to increase over most of the African continent (the central Sahel, east and central Africa), while precipitation is projected to decrease over the western Sahel and south-eastern Africa. We document the impact of climate change on extreme precipitation events. We also explain the uncertainty in simulated changes in precipitation and discuss ways to improve the reliability of projections.</p
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Recommended from our members
The Impact of Meteorology on Smoke and Low-level Clouds over the Southeast Atlantic
No full textIn this dissertation, we use radiosondes and satellite observation, reanalysis datasets, as well as radiative and trajectory models to document the relationship between the low-level clouds, smoke and meteorology over the southeast Atlantic. The southeast Atlantic presents a natural environment with one of the world’s largest marine low-level clouds, occurring along with the largest consumption of biomass fire over the adjacent southern African continent. This combination results in an extensive region of above-cloud biomass burning aerosols (predominantly smoke) over the marine low-level clouds, whereby the elevated smoke could lead to the stabilization of the lower troposphere, reduction of the cloud-top entrainment, and the build-up of water vapor within the boundary layer, which may eventually lead to increases in cloud fraction and decreases in cloud-top heights, in a process called semi-direct aerosol effect. The smokes are transported at a preferred altitude (∼750hPa – 550hPa) by a background easterly winds between July and October. During the same period, strong surface winds and ocean-influenced cold surface temperature characterize the meteorology within the boundary layer. The marine low-level cloud region is also associated with strong climatological subsidence above it, and cloud-top temperature inversion layer. The meteorological variations occurring above and below the low-level clouds are capable of influencing the cloud properties, and therefore may confound with the aerosol effects, making the separation of the aerosol and meteorological influences, on the low-level cloud, a very difficult challenge. We address this problem by identifying the dynamical and thermodynamical variations above the low-level clouds during the the peak aerosol months (July–October). Specifically, three areas are explored in this dissertation: the convolution of the dynamical and moisture effects with shortwave-absorbing aerosols over the low-level clouds; the role of the mid-tropospheric easterly-transporting system on both the elevated smoke and the low-level cloud environments; and the synoptic-scale sensitivity of the low-level clouds to a range of interacting meteorological conditions, with and without the presence of the elevated smoke. First, the analysis of the radiosondes at St. Helena Island, a small island located approximately 1800 km offshore of continental Africa (15.9◦S, 5.6◦W), shows the presence of mid-tropospheric moisture within the smoke layer, and above the low-level clouds. The smoke layer has previously been associated with hot and dry layer, perhaps in analogy to the Saharan air layer. The mid-tropospheric moisture over the south-east Atlantic has not been previously documented, and it occurs more than 70% of the time between September and October. During the same months, as the aerosol loading increases, the amount of the mid-tropospheric moisture also increases. The result of the radiative transfer calculations shows that the mid-tropospheric moisture-induced longwave cooling accounts for about 30% of the aerosol-induced shortwave warming, within the smoke layer. At the cloud top, increased mid-tropospheric moisture could increase cloud-top heights by enhancing the downwelling longwave radiation at the cloud top, and potentially reducing the turbulent mixing within the boundary layer, which may ultimately reduce the cloud fraction. This process essentially opposes the cloud-thickening semi-direct aerosol effect due to the elevated smoke alone.
Dynamical changes occurring during the polluted condition over the southeast Atlantic include enhanced above-cloud warm horizontal temperature advection, and reduced subsidence. The flow is from the warmer adjacent continent air, and the warm advection directly above the marine low-level cloud is also capable of the increases in cloudiness through its influence on stability, that is separate from the stability associated with semi-direct aerosol effect. In addition, though a previous modeling study focussing on the southeast Atlantic has similarly identified the association between the elevated shortwave-absorbing aerosols (smoke) and the reduced subsidence, it remains unclear if the reduced subsidence is a response of the elevated aerosols alone, or an associated change in the above-cloud meteorological features, or both. Here, we show that during the September–October period, the southeast Atlantic is characterized by the Southern African Easterly Jet (AEJ-S), a region of maximum mid-tropospheric easterly winds responsible for the westward transport of both the aerosols and the moisture above the low-level clouds. The AEJ-S can be thought of as a southern counterpart of a better-known northern African easterly jet, and using the wealth of information available for the northern African easterly jet, we show that the AEJ-S is associated with induced upward motion directly below the jet, between 5◦S-15◦S. The AEJ-S-induced upward motion strengthens the large-scale ascent over the land, and therefore enhances the efficiency of trajectory-derived aerosol lifting emissions into the free-troposphere. Over ocean, the induced upward motion also reduces the large-scale subsidence over the marine low-level cloud. All else equal, the reduction of the offshore subsidence can be associated with reduction in nearby cloud fraction and increases in cloud-top heights, between 5◦S-15◦S. Between the effects of AEJ-S and the elevated aerosols on subsidence, the AEJ-S can be associated with 16% reduction in subsidence compared to 7% reduction by the elevated smoke-aerosols, between 5◦S-15◦S. By isolating the independent effects of selected above-cloud and surface-based meteorological influences during July–October period, it is shown that increases in lower tropospheric stability (LTS, defined as θ800hP a − θ1000hP a ), cold surface advection and warm 800 hPa horizontal temperature advection, all lead to increases in marine low-level cloudiness over the southeast Atlantic. In addition, the mid-tropospheric moisture is shown to independently result in reduction of cloud fraction, especially in the near- coastal region. Enhanced subsidence independently leads to increased cloudiness north of 20◦S, but decreased cloudiness south of 20◦S. The subsidence-induced reduction in cloudiness, south of 20◦S, contributes significantly to counteracting the stability-induced increases in cloudiness over the same region. When aerosol is present north of 20◦S, the effect of LTS on the low-level cloud is increased by about 13% over the region where the elevated aerosols are more likely separated from the underlying clouds, and by about 32% when the aerosols are more likely in contact with the underlying cloud layer. The results of this dissertation provide a detailed, useful meteorological context, highlighting new information, for the several multi-national upcoming field campaigns planned over the southeast Atlantic region. It also provides a useful understanding of the background dynamics and basic physical connections between the aerosols, the low-level clouds and the meteorology over the southeast Atlantic, that can be used in future studies involving aerosol-cloud-radiation interactions, and ultimately in numerical climate models to improve the estimation of climate sensitivity to subtropical low-level clouds.</p
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe 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
Get PDFWe 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
Adebiyi etal: absorption of shortwave radiation by North African dust
No full textThe codes and datasets contained here are for the paper with the information below
Titled: "North African dust absorbs substantially less solar radiation than estimated by climate models and remote-sensing retrievals"
Author: Adeyemi A. Adebiyi, Yue Huang, Bjørn H. Samset and Jasper F. Kok
Please see the ReadMe.txt for additional details.
------------------------
Corresponding Authors:
Adeyemi Adebiyi
Email: [email protected];
Department of Life and Environmental Sciences,
University of California-Merced,
5200 North Lake Road Merced, CA 95343
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
- …
