1,721,174 research outputs found
An Investigation into the Grade Dynamics of Drainage Implements
Full text linkThe use of the trenchless plough drainage implement has increased in the
past few years due to its efficiency and cost advantages over other
methods. However, the performance of these machines when working in fields
with irregular soil conditions is not yet satisfactory. It is important
therefore to study the soil parameters and conditions which could affect
the implement behaviour under these circumstances.
Therefore, a detailed investigation of the soil reaction forces acting
upon a scale model of the trenchless plough was conducted under
controlled conditions in a soil laboratory. The model was tested first
under restricted conditions of movement, in order to observe and determine
all the possible soil reaction forces.
The tine, due to its geometric characteristics, was classified as a very
narrow tine, and an existing model to predict the soil reaction force
acting on the front face of these tines was extended to predict the forces
on the sides. Since the length of the failure plane ahead of the tine is
often required in the investigation of the soil reaction forces, a
mathematical solution based on the Coulomb principle of Passive Earth
Pressure was presented to estimate the soil failure pattern. There was
good agreement between the values of the angle of the shear plane
predicted by this method and the experimental data obtained from the
glass sided tank tests.
Dynamic tests were conducted with the implement assembled with a long
floating beam arrangement assisted by a small link (free-link), used
between the hitch-point and the pivoted end of the beam. These tests
revealed that, when working over irregular soil conditions a better grade
control can be obtained if the hitch-point is kept at constant level in
reference to a desired line. In the case where field irregularities
persist for long (step inputs), corrections in the hitch-point height
might be necessary. These tests show that the implement depth changes in
different proportion in relation to the hitch-point height. Where no
control is imposed on the hitch-point, the path of the implement is
attenuated in relation to the hitch-point position, where better results
are obtained for high frequency of the hitch-point.
A mathematical solution based on these findings and on the dynamic balance
of the forces acting on the system was presented. Since it is an
interactive method and requires long and repetitive calculations, a
computer programme was developed and used to predict the response of the
implement under these uneven conditions. Good agreement between data and
estimated values suggested that the method is acceptable
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
An investigation into the mechanics of agricultural discs
Full text linkA prediction model
based
upon Mohr-Coulomb soil
mechanics
theory has been developed to predict the
interaction between the
soil and agricultural
discs
of
different
geometries and operating angles to both
vertical
and tilted discs. The model
is based
on two forms
of soil
failure. The magnitude of each
form
of
failure is depen-
dent
upon a passive reaction on the concave side of the
disc
and a vertical
bearing
reaction on the convex side
of the disc. The predicted results are
in
close agreement
with
the results of the experimental studies.
Disc geometry
is
one of the
most
important factors
to be
considered
in
evaluating the soil reaction acting
upon a
disc tool. A theoretical
analysis of the disc
geometry was
therefore carried out. The analysis of
the disc geometry makes
it
possible to determine the
factors required
for the predicted
forces
acting on a
disc tool.
The experimental studies were conducted
in a sandy
loam
soil at a moisture content
in the friable
range, under
controlled soil
bin
conditions. The
work was carried out
at
full-scale with
3 dimensional force
measuring apparatus
developed primarily
for this investigation. The discs
studied
had a range of
disc
angles
between 150 and
600
and a range of tilt angles between 0
and
35. The depth
of cut ranged
from 80
mm to 140
mm and at speeds
between 0.75 m/s and
1.5
m/s.
The disturbance
area of the soil caused
by the
rotating soil cutting
disc is
calculated to define the
disturbed
area
for
any combination of
disc
angle,
disc
diameter, gang spacing and
depth
of work
in order to
accurately calculate specific resistance.
Disturbance and soil
inversion
were
investigated
using transparent discs
and soil tracers, with a variety
disc
and
tilt angles
in
order to quantify
inversion
and mixing
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
An investigation into the design of precision weeding mechanisms for inter or intra-row weed control
Full text linkThere is an increasing interest in the use of mechanical intra-row weeders because of
concern over environmental degradation and a growing demand for organically
produced food. The aim of this study was to investigate the factors that influence the
design of precision weeding mechanisms for inter-and intra-row weed control. The
purpose is to increase the understanding of the dynamics of the soil-machine
interactions and to develop a system for either organic farming or to reduce the
environmental loading of agrochemicals in conventional agriculture.
Both the graphical computer simulation studies and the use of a mathematical model
(O’Dogherty et al., 2007) for the kinematics of discs were used as tools to aid the disc
design to determine the optimum geometric characteristics for a rotating disc that will
be able to treat the intra-row area between the crop plants undisturbed circle. The
model has wide applicability for the interactive design of discs for a range of crops.
A force prediction model for shallow asymmetric static and rotating discs (about a
vertical axis) developed to predict the forces on rotating discs. The model takes into
account the geometric parameters of the discs, the speed of operation, the working
depth and the physical properties of the soil based upon those required for the general
soil mechanics equation which obeys the Mohr-Coulomb failure criterion. A
comparison of all experimental work encompassing the laboratory experiments with
non-rotating and rotating discs, incorporating the deflection effect of the shaft when
working at 0o inclination angle showed that the model is able to predict the draught
force with good accuracy. The predicted forces were 3.5% more than the measured
forces overall for a linear regression line (with a coefficient of determination of 0.7)
and 61% of the data were within bounds of ± 25% a line of equal magnitude.
The effect of working depth, inclination angle and disc geometry on draught and
penetration force requirements for flat and convex discs were assessed under
controlled laboratory conditions. Because of its simplicity a flat disc was an obvious
one to study as it is a circular blade with incorporating a cut-out sector, whilst the convex disc has the advantage of underside clearance. The effect of the concavity on
soil failure proved to be of interest by providing smaller aggregates. Four inclination
angles (0o - 15o) were examined at 0.5 m s-1 (1.8 km h-1) driving speed and 1 rev s-1
rotational speed at 10 mm deep. Four depths (10 mm - 25 mm) were examined at 0.5
m s-1 driving speed and 1 rev s-1 rotational speed at 10 mm deep and 0o inclination
angle were tested under controlled conditions. Inclination angle and disc geometry
had a significant effect on disc forces and soil failure. A small increase in inclination
angle to the direction of travel reduces the magnitude of draught and vertical force by
70% and 80% respectively on average for both flat and convex disc geometries. The
convex disc requires 15% less draught force than an equivalent flat disc. This allowed
the optimum working parameters for a disc to be selected to eliminate the weeds with
the minimum force requirements.
The results of a field experiment after 16; 23; and 33 days transplanting with a
working speed of 0.5 m s-1 (1.8 km h-1) showed that the proposed novel mechanical
weed control system can achieve a weed reduction within the crop row up to 87%.
The disc-hoe has a lower cost for an area of 125 ha of £81 ha-1,in comparison to £139
ha-1 for the inter-row and hand weeding combination and £690 ha-1 for a six man gang
manual intra-row weeding, for two passes. It is also less expensive than the cost of the
24 m tractor mounted sprayer of £100 ha-1
The use of the rotating disc-hoe for mechanical weed control would have the benefits
of lower mechanical weeding cost, increased potential for organic production and
reduction in the number of weeding operations through better targeting to minimise
problems caused by frequent soil disturbance and reduced herbicide use having the
benefits of environmental advantage
Kenya : the struggle for a new constitutional order
No full textThe aftermath of recent Kenyan elections has been marred by violence and an apparent crisis in democratic governance, with the negotiated settlement resulting from the 2007 election bringing into sharp focus longstanding problems of state and society. The broader reform process has involved electoral, judicial and security-sector reforms, among others, which in turn revolve around constitutional reforms. Written by a gathering of eminent specialists, this highly original volume interrogates the roots and impact of the 2010 constitution. It explains why reforms were blocked in the past but were successful this time around, and explores the scope for their implementation in the face of continued resistance by powerful groups. In doing so, the book demonstrates that the Kenyan experience carries significance well past its borders, speaking to debates surrounding social justice and national cohesion across the African continent and beyond.CONTENTS: Part One: Contexts and actors in the making of a new constitution -- 1. The protracted transitions to the Second Republic in Kenya - Paul Tiyambe Zeleza -- 2. Fuelling the violence: the print media in Kenya's volatile 2007 post-election violence - Sammy Gakero Gachigua -- 3. Mediating Kenya's post-election violence: from a peace-making to a constitutional moment - E. Njoki Wamai -- 4. Instrumentalism and constitution-making in Kenya: triumphs, challenges and opportunities beyond the 2013 elections - Raymond Muhula and Stephen Ndegwa -- 5. Revisiting 'the two faces of civil society' in constitutional reform in Kenya - Wanjala S. Nasong'o -- Part Two: The content, challenges and opportunities of a new constitutional order -- 6. Constitutions and constitutionalism: the fate of the 2010 Constitution - Yash Pal Ghai -- 7. Elite compromises and the content of the 2010 constitution - Godwin R. Murunga -- 8. Security and human rights in the new constitutional order in Kenya - Mutuma Ruteere</p
Kenya : the struggle for a new constitutional order
No full textThe aftermath of recent Kenyan elections has been marred by violence and an apparent crisis in democratic governance, with the negotiated settlement resulting from the 2007 election bringing into sharp focus longstanding problems of state and society. The broader reform process has involved electoral, judicial and security-sector reforms, among others, which in turn revolve around constitutional reforms. Written by a gathering of eminent specialists, this highly original volume interrogates the roots and impact of the 2010 constitution. It explains why reforms were blocked in the past but were successful this time around, and explores the scope for their implementation in the face of continued resistance by powerful groups. In doing so, the book demonstrates that the Kenyan experience carries significance well past its borders, speaking to debates surrounding social justice and national cohesion across the African continent and beyond.CONTENTS: Part One: Contexts and actors in the making of a new constitution -- 1. The protracted transitions to the Second Republic in Kenya - Paul Tiyambe Zeleza -- 2. Fuelling the violence: the print media in Kenya's volatile 2007 post-election violence - Sammy Gakero Gachigua -- 3. Mediating Kenya's post-election violence: from a peace-making to a constitutional moment - E. Njoki Wamai -- 4. Instrumentalism and constitution-making in Kenya: triumphs, challenges and opportunities beyond the 2013 elections - Raymond Muhula and Stephen Ndegwa -- 5. Revisiting 'the two faces of civil society' in constitutional reform in Kenya - Wanjala S. Nasong'o -- Part Two: The content, challenges and opportunities of a new constitutional order -- 6. Constitutions and constitutionalism: the fate of the 2010 Constitution - Yash Pal Ghai -- 7. Elite compromises and the content of the 2010 constitution - Godwin R. Murunga -- 8. Security and human rights in the new constitutional order in Kenya - Mutuma Ruteere</p
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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