1,721,043 research outputs found
Dual-Diameter Drip Laterals Laid on Flat Fields: Modelling and Measurements
No full textRecently, under the assumption of constant emitter flow rate, simplified procedures to design microirrigation units without using pressure compensating emitters (PC) have been suggested, and a software named IRRILAB, allowing for saving energy and not considering local losses due to the emitters insertions, was developed. The principle of IRRILAB software in saving energy is based on the rationale that the entire admitted range of pressure head variation, established by a design unit pressure head tolerance, must be used during the irrigation system operation. Moreover, it was demonstrated that if the lateral pressure head tolerance is sufficiently tight, the constant emitter flow rate assumption provides negligible errors in the pressure head distribution (PHD), compared to the numerical solution derived by the exact stepwise approach. By using the same IRRILAB approach, for laterals laid on flat fields, this paper extends the simplified solutions to dual-diameter laterals, also considering local losses that for a high number of the emitters might not be negligible. Simple relationships for the pressure head tolerances of the dual-diameter laterals and the characteristics of the emitters are presented, the latter helping to select the commercial non-pressure compensating emitters (NPC). The procedure was positively tested through numerical and experimental tests
Closed circuits of drip laterals versus open circuits: hydraulic performance and energy-saving potential
No full textDrip irrigation systems are usually designed according to open circuits, characterised by branching pipe networks with many drip laterals and one manifold. However, the closure of the circuits with a secondary manifold connecting lateral ends makes it possible to apply a lower inlet pressure head than open circuits, with important implications in energy-saving. In this paper, a comprehensive comparison between the hydraulic performance of open and closed circuits of drip laterals is carried out. The open circuits (op) were analysed by using IrriLab software, which requires two arbitrarily set pressure head tolerances, one for the laterals (delta L) and one for the manifold (delta M), determining the pressure tolerance of the unit (delta op). Meanwhile, the closed circuits were analysed using the well-known Hardy Cross method (HCM). For #3800 drip irrigation units characterised by different geometric and hydraulic parameters, an approximated relationship is derived to accurately predict the energy saving associated with the closure of the open circuits. Results showed that open circuits are recommended when designing for low delta M (low-pressure head variability in the manifold), since energy can be saved, although higher inside manifold diameters are required in this case. Contrarily, for high delta M, the closure of the circuit is more appropriate to save energy, since the inlet pressure head is much lower than that required by open circuits
Impact of solar panels on runoff generation process
Get PDFBecause of the benefits of solar energy, solar photovoltaic (PV) technology is being
deployed at an unprecedented rate and the number of photovoltaic panels is sharply
increasing. Agrophotovoltaic systems (solar farms) seem to be the most sustainable
tools to create renewable energy without compromising agricultural production.
However, utility-scale solar energy development is land intensive and its large-scale
installation can have negative impacts on the environment. Moreover, its impacts on
soil and on relative hydrological processes have been poorly studied. This article aims
to evaluate the impact of solar panels on the runoff generation process, which is
directly linked to the soil erosion process. Using a rainfall simulator, runoff measurements
for a rainfall intensity equal to 56 mm/h were carried out by assuming different
panel arrangements with respect to the maximum slope direction of the field
(cross slope and aligned slope). Results were compared to a control reference of the
same plot, with no panels (bare soil). Physical models found in the literature were
then applied and calibrated, to upscale the models to a much higher hillslope length.
Results showed that solar panels increase the peak discharge by about 11 times compared
to the reference hillslope. A moderate effect of PV panel arrangement was
observed on the peak discharges (11.7 and 11.5 times higher, for cross slope and
aligned slope panels, respectively), whereas the time to runoff was the lowest for
aligned slope panels (0.3 h), higher for cross slope panels (0.62 h), and the highest
(1.2 h), for the bare soil hillslope. As it would be expected, upscaling the models to
longer hillslopes resulted in increases in outlet discharges, and in the time to runoff,
with an exception for aligned slope panels
Applying the Hardy Cross method to assess the energy-saving associated with closed circuits in drip irrigation systems compared to open circuits
Get PDFThe analysis of a looped water distribution system, usually employed in subsurface drip irrigation
(SDI), under pressure and steady-state conditions, can be successfully performed if the topology of
the network, the structure pipes, and the discharges at the nodes are known (Wang et al., 2021).
Solving these complex networks usually requires an iterative approach. The Hardy Cross method
(HCM), which was originally developed in 1936 (Cross, 1936) for manual calculations in civil
engineering, can also be applied in lopped drip irrigation systems. This approach relies on the
successive addition of flow-rate adjustments in each pipe to achieve the energy balance in each
network segment, although limited by the Darcy-Weisbach resistance equation where the
discharge exponent is set to 2.
In this work, a reformulated HCM was applied to looped drip irrigation systems, considering both
local losses due to emitters’ insertion and the Hazen-Williams resistance equation (discharge
exponent = 1.852), which is better suited to describe friction losses in the commonly used
polyethylene pipes. The hydraulic performance of closed circuits calculated by HCM was analysed
and compared with that of open circuits designed by IRRILAB software application (Baiamonte,
2018).
In particular, the final objective is to assess the energy-saving provided by the closed circuits (cc) in
drip irrigation systems with respect to open circuits (oc). The energy-saving amount is expressed
as the ratio (hratio < 1), between the inlet pressure head, hin, of the closed circuit and that of the
open circuit. A predictive relationship of hratio was calibrated for 3000 simulations carried out for
rectangular irrigation units characterized by different geometry, pipe diameters, emitters’ spacing
and flow rate, providing relative errors RE < 0.25%. The results show that hratio depends on the
pressure head tolerance of the manifold, δM, associated with the open circuits, which IRRILAB
requires as an input parameter. This is very reasonable since, for high δM, the discharge circulating
in the manifold is also high and closing the circuits provides low hratio (hin cc << hin oc). The vice
versa occurs for low δM. Contrarily, the number of drip laterals, Nrows, has only a marginal effect on
hratio. Of course, the energy-saving benefit should also consider the higher investment costs of
cc than oc. However, this issue is beyond the scope of this study
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
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
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