19,913 research outputs found
Effects of Irrigation and Tree Spacing on Soil and Air Temperature Profiles of Olive Orchards
Changes on the climate of the boundary layer occur when a vegetation cover
above a bare soil is introduced, namely on temperatures and humidity profiles,
above and under soil surface. Since air and soil temperatures affect crop growth and
development and also soil moisture, they have been used as driving variables in
numerous crop growth and development models as well as in those referred to soil
mineralization, evaporation, transpiration, etc. The aim of this work was to evaluate
(a) the soil thermal behavior in two olive orchards (Olea europaea sp. europaea),
both grown on soils with little profile development (Regosol and Cambisol) and
subject to drip irrigation but with different spacing between trees, and (b) the air
thermal profile over olive rows. Experiments were performed from April to June
2012 in Southern Portugal. Soil and air temperatures were measured by
thermocouples. The two orchards changed spatial distribution of soil surface
temperature, soil temperature profiles and air temperature within the canopy, either
on a daily or hourly basis. Olive tree spacing and irrigation affected both the soil
thermal behavior and air thermal profiles. Tree spacing affected the horizontal
gradients established along the interrows (intensity and rhythm). Irrigation reduced
hourly and daily mean soil surface temperatures and daily thermal amplitudes of
both profiles. Differences were also found on damping depths of the thermal wave
estimated for the driest and the wettest profiles. Along the row, the effect of shading
seems to overlap that of irrigation in a hourly basis
Local Physical Coodinates from Symplectic Projector Method
The basic arguments underlying the symplectic projector method are presented.
By this method, local free coordinates on the constrait surface can be obtained
for a broader class of constrained systems. Some interesting examples are
analyzed.Comment: 8 page
A linear programming based heuristic framework for min-max regret combinatorial optimization problems with interval costs
This work deals with a class of problems under interval data uncertainty,
namely interval robust-hard problems, composed of interval data min-max regret
generalizations of classical NP-hard combinatorial problems modeled as 0-1
integer linear programming problems. These problems are more challenging than
other interval data min-max regret problems, as solely computing the cost of
any feasible solution requires solving an instance of an NP-hard problem. The
state-of-the-art exact algorithms in the literature are based on the generation
of a possibly exponential number of cuts. As each cut separation involves the
resolution of an NP-hard classical optimization problem, the size of the
instances that can be solved efficiently is relatively small. To smooth this
issue, we present a modeling technique for interval robust-hard problems in the
context of a heuristic framework. The heuristic obtains feasible solutions by
exploring dual information of a linearly relaxed model associated with the
classical optimization problem counterpart. Computational experiments for
interval data min-max regret versions of the restricted shortest path problem
and the set covering problem show that our heuristic is able to find optimal or
near-optimal solutions and also improves the primal bounds obtained by a
state-of-the-art exact algorithm and a 2-approximation procedure for interval
data min-max regret problems
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