1,721,064 research outputs found
Experimental study of the implement-and-tractor aggregate used for laying tracks of permanent traffic lanes inside controlled traffic farming systems
No full textTraffic-induced soil compaction is a serious drawback of modern agriculture. However, controlled traffic farming (CTF) systems, which have been adopted worldwide, are useful strategies of lessening this problem. In CTF systems, the crop zone is clearly separated from the permanent traffic lanes (PTL), which are used exclusively for the movement of the machine-and-tractor aggregates. The CTF systems are implemented both with and without the use of the GPS systems. When navigation-aid is not used, the first positioning of the PTL tracks is an essential operation, in which the aggregate intended for this task must perform a sufficiently straight movement. This paper reports the assessments concerning the PTL tracks laid by an experimental aggregate, which consisted of a four-wheel drive tractor and a tillage implement operating in the “push” mode. This aggregate formed tracks with a sufficiently small dispersion (10.30 cm2) and a fairly low (not more than 0.09 Hz) frequency of their fluctuations in a horizontal plane. Furthermore, during the tests, a rather close positive correlation between the bearing angle φ of the tractor and the turning angle α of its driven wheels was registered and the maximum value of the related correlation function was 0.9. Moreover, the phase (time) shift between the disturbing torque and the response to it by the tractor operator did not exceed 0.75 s. The use of the proposed aggregate allowed laying tracks with a depth of 21.2 ± 0.3 cm and vibrations in a longitudinal vertical plane, whose dispersion was not more than 2 cm2 and was concentrated in a fairly narrow frequency range from 0 to 1.78 Hz
A theoretical study of the limit path of the movement of a layer of soil along the plough mouldboard
Full text linkThere have been studied regularities affecting the magnitude of the dynamic component of the plough resistance for cylindrical mouldboards, and its peculiarities for cylindroid mouldboards depending on the direction of arrival of the soil layer on the ploughshare. The dynamic component of the draught resistance of the plough, which is directly proportional to the square of the ploughing velocity, can be estimated by the value of a dimensionless coefficient, conditionally named the "wrapping angle of the layer". This coefficient can be found for the mouldboard surface if the path of the movement of the mid-point of the section of the soil layer is known. By example of a cylindroid surface of the mouldboard it is shown how the dynamic component of the resistance varies depending on the design parameters of the mouldboard and the direction of arrival of the soil layer onto the ploughshare. As a result of the experimental study, a reduction of the longitudinal component of the thrust on the plough body, equipped with a mouldboard with an improved design made according to the results of the theoretical study, was achieved. This reduction was obtained by reducing the friction force due to the dynamic component of the resistance forces
Theoretical Study of Transverse Offsets of Wide Span Tractor Working Implements and Their Influence on Damage to Row Crops
Full text linkWide span tractors have a wide transversal bar, on which different implements can be mounted, while the supporting wheels follow the set trac-lanes. The stability of wide span tractor movement is influenced by unbroken small angular deviations and transversal displacements of the machine due to several factors. These deflections from the set trajectories affect the working implements, especially the peripheral ones, which can cut the plants if wide span tractors are used to manage row crops. In this context, it needs to consider a safeguard zone that allows to reduce the probability of contact between working implements and plants. The aim of this paper was to determine the quantitative effect of transverse displacements of the working implements and the suitable size of the aforesaid safeguard zone. The magnitude of the inner and outer displacements of the working implements depends significantly on their location in relation to the center of the wide span tractor. For working implements located outside the center of the tractor, the outer safeguard zone should be larger than the inner zone. The probability of crop damage by working implements can be reduced by automated control of wide span tractor movement
Dynamics of Temperature Variation in Soil under Fallow Tillage at Different Depths
Full text linkOne of the important processes taking place during soil surface tillage is the variation of the soil temperature at different depths. The paper presents the results of research into the dynamics of soil temperature variation in terms of such parameters of the soil as its thermal diffusivity and temperature oscillation frequency. It has been established that the temperature oscillation amplitude decreases when the depth increases, following the logarithmic law. In this variation, the temperature difference between the 0–5 cm layer and the adjacent 5–10 cm layer has the greatest value. This circumstance is a favorable factor for the fallow tillage technology, where the soil is regularly cultivated to a depth of no more than 5 cm, in case of a moisture deficit. A decrease in the frequency of the soil temperature oscillations can result in the reduced level of its heating in different layers. In terms of qualitative changes, the reduction in soil thermal diffusivity results in the amplitude of the soil temperature oscillations being lowered and at the same time the maximum of these oscillations being shifted towards a delay
The effect of a lateral airflow created on nozzle tip on the spray droplets deposition
Full text linkImproved application efficacy of a plant protection products by using a pneumatic device to change the dispersion of spray droplets is depended on the intensity of crosswind. The laboratory investigations of the spraying process of plants by means of the nozzles of a pneumatic system determined the quality indicators of pressure in the injection process of 0.4 MPa – the droplet coating density of 19–46 pcs cm2 –1 for the weighted mean droplet diameters (WMD) in the other experimental variants was within 304–543 μm. These indicators were compared with those for the standard, anti-drift and air injection nozzle types in which the droplet coating density was 23–59 pcs cm2 –1 and the weighted mean droplet diameters (WMD) were in the range of 350 to 485 μm. An analytical dependence was obtained of the influence of the lateral airflow and air pressure in the pneumatic system upon the amount of the deposited spray liquid
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
Theoretical Studies of the Relationship Between the Parameters of the Bridge Tractor and the Engineering Area of the Field
No full textThe planning of the field under the bridge system of agriculture should be carried out taking into account the size of both the bridge tractor, which moves on specially created tracks of the permanent technological track, and auxiliary means of mechanization. The purpose of the research is to study the processes of field planning and organization of the movement of bridge tractors, considering the prospects for further automation of all technological processes that they perform, including transport. Theoretical research was carried out by modeling the conditions of the bridge tractor operation on the PC using the provisions of theoretical mechanics and tractor theory. Experimental studies of the bridge tractor were carried out according to both generally accepted and developed methods and involved the use of modern and specially designed equipment. As a result of research, mathematical models and algorithms were developed to allow interdependent choice of construction parameters of bridge tractors, in particular, the width of its track and propulsion, stable traffic conditions (taking into account the value of technological tolerance) and parameters of the field for its permanent technological track. Mathematical analysis of the obtained models substantiates the rational track width of these bridge tractors at the level of 7.5...9 m, according to which the loss of field area under the engineering zone when using them is not more than 5...6%
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
- …
