1,720,977 research outputs found
The Effect of Heating on Properties of Sandy Soils
Full text linkAlthough burning grass and crop residues is prohibited in many countries, farmers perceive
it as a quick and inexpensive way to eliminate unwanted biomass. The aim of this study was to
estimate the impact of heating temperature (simulation of biomass burning) on the studied properties
(soil organic carbon (SOC) content, pH(H2O), water drop penetration time, WDPT, and contact
angle, CA) of acidic sandy soils. Soil samples were taken from the experimental sites S1, S2, and
S3 at Studienka village in the Borská nížina lowland (southwestern Slovakia). Experimental site S1
was arable land, experimental site S2 was arable land abandoned for approximately 10 years, and
experimental site S3 was arable land abandoned for approximately 30 years with scattered Scots pine
(Pinus sylvestris L.) trees. It was found that all the soil properties studied were strongly affected by
heating. A drop in SOC was observed in all the soils for the heating temperature between 20 and
600 °C. Due to the incomplete combustion of SOC, a small (0.1–0.7%) SOC content was recorded
even in soils heated to between 600 and 900 °C. An increase in pH(H2O) was observed in all the
soils for the heating temperature higher than 300 °C. Soil from the experimental site S1 was wettable
(WDPT < 5 s) for all of the heating temperatures. WDPT vs. heating temperature relationships for
the soils from the experimental sites S2 and S3 were more complex. After a decrease in the heating
temperature of 50 °C, an increase in WDPT for the heating temperature between 50 °C and 300 °C
(for S3 soil) and 350 C (for S2 soil) was registered. Finally, the WDPT dramatically dropped to 0 for
the heating temperature of 350 °C (for S3 soil) and 400 °C (for S2 soil). CA started to decrease at
300 °C in all the soils and dropped to 0° for all the soils at 800 °C. CA > 0° measured in soils for the
heating temperature between 400 and 800 °C, as a consequence of the small SOC contents due to
the incomplete combustion of SOC, is a novelty of this study which demonstrates that CA is more
sensitive to the changes in subcritical water repellency than WDPT
Effects of vegetation at different succession stages on soil properties and water flow in sandy soil
No full textThe effects of vegetation at different succession stages on soil properties and water flow were assessed in sandy soil at 3 experimental sites near Sekule village (southwest Slovakia). Site S1 was a pioneer site dominated by mosses, site S2 was an early successional stage with a thin stand of grasses, and site S3 was an early successional stage (more advanced compared to the previous), richer in species, with a denser stand of grasses. It was found that vegetation at different succession stages affected soil properties and water flow in sandy soil, but the order of changes in some soil properties and water penetration depths were different from the order of succession stages
Alternative analysis of transient infiltration experiment to estimate soil water repellency
No full textThe repellency index (RI) defined as the adjusted ratio between soil-ethanol, S e , and soil-water, S w , sorptivities estimated from minidisk infiltrometer experiments has been used instead of the widely used water drop penetration time and molarity of ethanol drop tests to assess soil water repellency. However, sorptivity calculated by the usual early-time infiltration equation may be overestimated as the effects of gravity and lateral capillary are neglected. With the aim to establish the best applicative procedure to assess RI, different approaches to estimate S e and S w were compared that make use of both the early-time infiltration equation (namely, the 1 min, S1, and the short-time linearization approaches), and the two-term axisymmetric infiltration equation, valid for early to intermediate times (namely, the cumulative linearization and differentiated linearization approaches). The dataset included 85 minidisk infiltrometer tests conducted in three sites in Italy and Spain under different vegetation habitats (forest of Pinus pinaster and Pinus halepensis, burned pine forest, and annual grasses), soil horizons (organic and mineral), postfire treatments, and initial soil water contents. The S1 approach was inapplicable in 42% of experiments as water infiltration did not start in the first minute. The short-time linearization approach yielded a systematic overestimation of S e and S w that resulted in an overestimation of RI by a factor of 1.57 and 1.23 as compared with the cumulative linearization and differentiated linearization approaches. A new repellency index, RI s , was proposed as the ratio between the slopes of the linearized data for the wettable and hydrophobic stages obtained by a single water infiltration test. For the experimental conditions considered, RI s was significantly correlated with RI and WDPT. Compared with RI, RI s includes information on both soil sorptivity and hydraulic conductivity and, therefore, it can be considered more physically linked to the hydrological processes affected by soil water repellency
Evaporation from soils of different texture covered by layers of water repellent and wettable soils
Full text linkWater repellent soils are able to channel water deep into the soil profile by fingered flow, minimising water storage in the water repellent top layer where water is most susceptible to evaporation. To date, the effect of water repellent or wettable surface layer on evaporation from wet sublayer has only been reported for coarse materials, and an increase in water repellency led to a greater delay in water evaporation. The objective of this study was to assess the effect of water repellent vs. wettable top layers with different thickness on water evaporation from coarse and fine texture subsoils that were pre-moistened. Clay loam soil samples were taken from Pinus pinaster woodland of Ciavolo, Italy, and sandy soil samples from Pinus sylvestris woodland of Sekule, Slovakia. Evaporation from soil samples was determined from the loss of weight in laboratory conditions. Water in the clay loam soil from Ciavolo was held for a longer period due to slower evaporative loss than in the sandy soil from Sekule, and the impact of the water repellent layer on the loss rate over time is related to its thickness. Over 550 h, about 90% of the initial stored water was evaporated from the uncovered clay-loam soil sample from Ciavolo. In the same time, the 0.3, 1, and 2 cm-thick duff layers, respectively, saved about 23, 34, and 58% of water from evaporation, and evaporation of 90% of water took over 780, 1100, and 1450 h. It means that the clay loam soil cover with the 0.3, 1, and 2 cm-thick duff layers resulted in prolonging the evaporation by 10, 23, and 37.5 days, respectively. As to the sandy soil from Sekule, 98% of water was evaporated from the uncovered soil sample over 240 h. In the same time, the 0.3, 1, and 2 cm-thick water repellent soil layers, respectively, saved about 7, 45, and 59% of water from evaporation, and evaporation of 98% of water took over 330, 606, and 774 h. It means that the sandy soil cover with the 0.3, 1, and 2 cm-thick water repellent soil layers resulted in prolonging the evaporation by about 4, 15, and 22 days, respectively. It can be concluded that water repellent surface layers, created by pine trees, are able to delay evaporation significantly for both coarse and fine textured soils, which may be particularly beneficial for plants during hot and dry periods in summer
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
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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