1,804 research outputs found
Bi-Hamiltonian Aspects of a Matrix Harry Dym Hierarchy
We study the Harry Dym hierarchy of nonlinear evolution equations from the
bi-Hamiltonian view point. This is done by using the concept of an S-hierarchy.
It allows us to define a matrix Harry Dym hierarchy of commuting Hamiltonian
flows in two fields that projects onto the scalar Harry Dym hierarchy. We also
show that the conserved densities of the matrix Harry Dym equation can be found
by means of a Riccati-type equation.Comment: Revised version, 22 pages; a section on reciprocal transformations
added. To appear in J. Math. Phys
Verifying a stochastic model for the spread of a SARS-CoV-2-like infection: opportunities and limitations
There is a growing interest in modeling and analyzing the spread of diseases
like the SARS-CoV-2 infection using stochastic models. These models are
typically analyzed quantitatively and are not often subject to validation using
formal verification approaches, nor leverage policy syntheses and analysis
techniques developed in formal verification. In this paper, we take a Markovian
stochastic model for the spread of a SARSCoV-2-like infection. A state of this
model represents the number of subjects in different health conditions. The
considered model considers the different parameters that may have an impact on
the spread of the disease and exposes the various decision variables that can
be used to control it. We show that the modeling of the problem within
state-of-the-art model checkers is feasible and it opens several opportunities.
However, there are severe limitations due to i) the espressivity of the
existing stochastic model checkers on one side, and ii) the size of the
resulting Markovian model even for small population sizes.Comment: Accepted for pubblication in AIxIA 202
Development of machines for flaming weed control on hard surfaces
Weed control is a major issue not only in agriculture but also on hard surfaces in urban and suburban
contexts. Weeds can cause serious damage to urban structures and are often considered as a sign of neglect. Moreover,
citizens are becoming increasingly aware of environmental pollution and its potential risks for their health.
Flaming represents a concrete alternative to herbicide applications on hard urban surfaces. Flaming can also be a
good alternative to mechanical means (e.g., string trimmers) which can seriously damage surfaces because they are too
intense and in any case are often not effective. The aim of this work is to describe LPG fed flaming machines designed and
built at the University of Pisa, Italy. Liquefied Petroleum Gas (LPG) is a flammable mixture of hydrocarbon gases–
propane and butane. Four different machines were developed and tested in four different urban and sub-urban contexts. A
small backpack flamer equipped with a manual lance was tested on a stonewall, a trolley machine with a manual lance
was used to clean the base of ornamental trees, a self-propelled machine was tested in a railway station, and a mounted
machine was used in a suburban cycle way. Flaming was compared to the ordinary weed control systems such as using
herbicides or mowing.
The results showed that flaming can be both less expensive and more effective (on average less that 1 € m-2 year-1
maintaining weed cover below 5% to 6%) than the ordinary treatments in urban areas. Flaming was more effective than
mowing in the suburban area but much more expensive, thus an integrated approach would be advisable in this context.
Future research should be devoted to improving the efficiency of the treatment, using for example, new burners with
secondary air and precision agriculture technologies
Physical weed control in urban hard surfaces and turfgrasses.
Weed management is a major issue not only in agriculture but also in cities and in public and sport turfs. Weed development often generates negative aesthetic effects, a sense sloppiness, mechanical damages to hard surfaces, the reduction of visibility for drivers, the reduction of the quality of the quality of the turf, and can make difficult for pedestrians to walk.
Specific trials were carried out in order to develop and set up machines and techniques for weed control in urban and sub-urban areas and on turfs
Application of precision flaming to maize and garlic in the RHEA Project.
Flame weeding is actually a well known and used
physical treatment according to the increase in concerns about
the effects of herbicides on human health and the environment
and in the light of the new European laws. Flaming historically,
was used at first as a pre-emergence treatment, both prior to
planting and before crop emergence. Alternatively, flaming can
be used also selectively after crop emergence or planting in
tolerant species. Although inter-row weeds can be effectively
controlled through mechanical cultivation, weeds that grow in
the row are more difficult to control as, in some cases,
cultivation is both ineffective and causes unacceptable levels of
crop damage. This work aims to describe the specific machine
for mechanical-thermal weed control which is being realized by
the University of Pisa within the RHEA project. This machine is
able to perform mechanical and thermal treatments at the same
time in order to remove weeds mechanically from the inter-row
space and perform in-row selective and precision flaming. The
project is still on-going and the machine has not been fully
realized and tested yet, thus no data is available at the moment
LPG burners for weed control
This article reports on the results of a study carried out on three prototypes of open flame burners for thermal weed control. Their performance is reported in terms of flame temperature and length, in order to ascertain the best ratio between primary and secondary air, and liquefied petroleum gas (LPG) consumption. To find the best ratio between primary and secondary air, the length and temperature of the flame were recorded for each of the three burners, examined by varying the inlet sections of the primary air and secondary air. The data on temperature and the flame length of each burner were processed using multiple regression analysis. The LPG consumption was determined with one of the burners using 10 different pressures in combination with three nozzles. The data obtained were subjected to non-linear regression using two gaseous outflow models. The various combinations of primary and secondary air inlet sections affected the values of the flame length and temperature. In general, the best combinations of primary and secondary air inlet for flame temperature did not correspond to those for flame length. However, this experiment showed that the inlet of secondary air is critical for the performance of this type of burner, in terms of flame temperature. The fuel consumption trial showed that the model proposed for the gaseous outflow is suitable for describing the values of LPG consumption collected during the trial. © 2015 American Society of Agricultural and Biological Engineers
Mechanical weed control on small-size dry bean and its response to cross-flaming
Dry bean (Phaseolus vulgaris L.) can be a profitable crop for farmers; however controlling weeds effectively without a decrease in yield remains a problem. An example where mechanical weed control is difficult to conduct is dry bean ‘Toscanello’, which is a small sized high-income niche product growing low to the ground. Concerning intra-row weed control, also flame weeding could be an opportunity but the dry bean heat tolerance needs to be studied. The aims of this research were to study the weed control efficacy of a spring-tine harrow and an inter-row cultivator in this bean variety, and to test the tolerance of dry bean cultivated under weed-free conditions to cross-flaming applied with different liquefied petroleum gas (LPG) doses. Flame weeding was applied at BBCH 13 and BBCH 14 bean growth stages by pairs of burners producing direct double flame acting into the intra-row space, with bean plants placed in the middle. The results suggest that the spring-tine harrow used two times at BBCH 13 and 14, respectively, lead to a yield similar to that of the weedy control. The inter-row cultivator could be an opportunity for small-sized dry bean crops producers, enabling them to obtain a similar yield compared to the hand-weeded control. Concerning the bean tolerance to cross-flaming the results showed that bean flamed at BBCH 13 stage had little tolerance to cross-flaming. Bean flamed at BBCH 14 stage was tolerant until an LPG dose of 39 kg/ha, giving yield responses similar to those observed in the non-flamed control
Cross-flaming application for intra-row weed control in maize
Flame weeding is the most common thermal intra-row weed control method used in agriculture as an alternative
to herbicides in heat-tolerant crops. Within the seventh framework program project “Robot fleets for Highly Effective Agriculture
and Forestry Management” (RHEA), the University of Pisa was responsible for the development of an automatic
machine for intra-row cross-flaming in maize (Zea mays L.). This study focused on the selection of a range of liquid petroleum
gas (LPG) doses able to control weeds without affecting crop yields, for the basic calibration of the machine. Tests
were conducted in 2012 and 2013 during the growing cycle of maize both in weed-free and real-field weedy conditions. Five
biological LPG doses (0, 52, 65, 104, and 130 kg ha-1) were applied at different maize growth stages once (2- and 5-leaf)
and twice (2-leaf the first time and 16 days after the first time). The response of maize and weeds to cross-flaming was
evaluated in terms of grain yield, weed density after flame weeding, and weed dry biomass at harvest. Log-logistic models
were used to describe the responses of different growth stages of maize and weeds to single and repeated applications of
LPG doses. Overall response of maize yield to flame weeding was influenced by LPG dose, number of flame weedings,
maize growth stage, and presence of weeds. The results of this study indicate that two cross-flaming treatments applied
separately with an LPG dose ranging from 36 to 42 kg ha-1 can provide an acceptable level of weed control in maize, enough
to ensure economically acceptable yields
RHEA project achievement: an innovative spray concept for pesticide application to tree crops equipping a fleet of autonomous robots. Report 1356
A combined flamer-cultivator for weed control during the harvesting season of asparagus green spears.
Weed competition during spears harvesting reduces asparagus yields. The application of herbicides during this period is illegal, and alternative non-chemical practices are needed. This research tested the effectiveness and efficiency of a custom-built combined flamer-cultivator to control weeds (both in the inter- and intra- spears production bands) during the spears harvest season. It also analysed the effects of various liquefied petroleum gas (LPG) doses on total asparagus yield, mean spear weight, and total number of marketable spears. In both years, the asparagus spears were generally not damaged by flame weeding using LPG doses of between 43 to 87 kg/ha. The same LPG doses were effective in controlling weeds, showing the same total marketable yields as the weed-free control. At high LPG doses (e.g. 130 and 260 kg/ha), yields decreased as a consequence of the damage caused to the spears, resulting in a lower number of marketable spears. Flaming did not affect the mean spear weight, and can be applied repeatedly during harvesting to maintain the weeds at a level that does not lead to a yield reduction. The repeated use of the combined flamer-cultivator (every seven days) led to higher yields than plots where weed control was not conducted. The new machine can be used in a period when herbicides are not possible. Flaming could be introduced by asparagus producers as an alternative, or in addition to herbicides applied in the pre-emergence and post-harvest of spears
- …