940 research outputs found
Actes de la première conférence régionale sur la lutte contre Miconia = Proceedings of the first regional conference on Miconia control
#Miconia Calvescens DC (Melastomataceae) est un arbre originaire des forêts humides d'Amérique tropicale, introduit comme plante ornementale en Polynésie Française et dans les îles Hawaï où il y constitue actuellement une plante envahissante majeure et y a été déclaré légalement espèce nuisible. Les objectifs de cette première conférence régionale sur la lutte contre #M. calvescens réunissant chercheurs et gestionnaires, sont de présenter le statut et la distribution actuelle de cette peste végétale dans les différentes zones envahies de la région du Pacifique (Polynésie Française, Hawaï, Australie), les méthodes de lutte déjà utilisées (lutte manuelle, chimique et biologique) ainsi que les stratégies de gestion appliquée
Calculating pH from EC and SAR values in salinity models and SAR from soil and bore water pH and EC data
Currently used soil salinity models do not contain a mechanism for including exchangeable
sodium effects on soil pH. A method is needed that allows pH calculation from the
sodium adsorption ratio (SAR) or exchangeable sodium percentage (ESP) and electrical
conductivity (EC) data. This study developed a simple method for calculating saturated
soil paste and aqueous solution pH from SAR (or ESP) and EC data and compared the
results with measured values from a number of soils and subsurface waters. The equation
pH - A+{B*(SAR)^1/2 /(1+C*EC)} estimated soil pH from EC and SAR or ESP values. When
rewritten as: SAR or ESP = {(pH-A)(1+C*EC)/B}^2 , the SAR or ESP was estimated from pH and
EC data. By using shallow bore (well) water and soil extract data from the Murray Basin,
values were determined for the scalar terms A, B and C. These values differed among
subsurface water and soil types, however, the range of each scalar was reasonably small.
It was found that a range of at least 2 - 5 pH units in the calibration data was necessary
to obtain reliable regression between predicted and measured pH and SAR or ESP values.
When these conditions were met, the predicted results were satisfactory. These relationships
provide a method for pH calculation in soil salinity models which takes into account soil
EC and sodium effects. They also provide a rapid field method to estimate SAR or ESP from
easily obtainable EC and pH data. Further research is needed to define the factors that
determine the values of A, B and C
The Optical Model Analysis of 200 MeV p + 16-O Elastic Scattering
This work was supported by the National Science Foundation Grant NSF PHY 81-14339 and by Indiana Universit
Purifying and Reversible Physical Processes
Starting from the observation that reversible processes cannot increase the
purity of any input state, we study deterministic physical processes, which map
a set of states to a set of pure states. Such a process must map any state to
the same pure output, if purity is demanded for the input set of all states.
But otherwise, when the input set is restricted, it is possible to find
non-trivial purifying processes. For the most restricted case of only two input
states, we completely characterize the output of any such map. We furthermore
consider maps, which combine the property of purity and reversibility on a set
of states, and we derive necessary and sufficient conditions on sets, which
permit such processes.Comment: 5 pages, no figures, v2: only minimal change
Understanding salt and sodium in soils, irrigation water and shallow groundwaters: A companion to the software program SWAGMAN-Whatif
Understanding Salt and Sodium in Soils, Irrigation Water and Shallow
Groundwaters is a companion booklet to SWAGMANe-Whatif, a computer
model that lets you see how salts, soils, water and water tables interact.
SWAGMANkWhatif also lets you assess the effects of management
practices that you might undertake in a particular area.
This booklet gives background information to help you understand salts,
sodium and their interactions with water and soils. It explains where
sodium and salts come from, how to identify salt-affected soils, and gives
instructions on taking soil and water samples for analysis. It also gives
suggestions on how to reduce the harmful effects of salts and sodium, and
tells you where to get advice in making reclamation and management
decisions for each situation.
Managing salt and sodium affected soils, together with waters used for
irrigation, is complex. It is not possible to cover all technical aspects or
possible treatment approaches in this booklet. Instead, we have given a
simple overview of the major principles involved in diagnosing and
managing salt and sodium affected soils and irrigation waters.
It is difficult to summarise salt and sodium effects on soils and plants
without using some technical terms, so a comprehensive glossary has been
included
SWAGMAN-Whatif, an interactive computer program to teach salinity relationships in irrigated agriculture
Managing salt-affected irrigated lands and marginally salinine
irrigation water requires understanding the interactions among
soil salinity, crop salt tolerances, soil physical properties, irrigation
water quality, irrigation management, water table depth
and quality, climate, and crop yield. An interactive computer
program was developed to simulate interactions among the
above factors. It shows how changing one factor impacts the
others for a growing season. The user selects a climate, crop, and
soil characteristics from menu lists, then sets the water table
depth and quality, irrigation water quality, and develops an
irrigation schedule. On execution, surface runoff, water table
rise or fall, and the relative yield reductions due to overirrigation,
underirrigation, and salinity are shown numerically for 1 yr.
Soil water content, soil salinity, water table depth changes, and
rain and irrigation events are also shown graphically. An IBM-compatible
computer with a math coprocessor executes the
program in 6 to 10 s. This is an educational tool designed to teach
the concepts of salinity and irrigation management and is not an
irrigation scheduling program nor a management tool. Two
versions have been developed, one using metric units, southern
hemisphere growing seasons, and Australian terminology; and
a second using northern hemisphere growing seasons and U.S.
units and terminology. The U.S. version also allows use of metric
units. The program is supplied in executable code with a user
guide, a soil salinity manual, and a salinity units conversion slide
rule
Predicting salinization in a heavy clay soil subjected to a saline shallow water table
Salt increase in a heavy clay soil due to capillary rise was simulated by an
analytical model and a numerical model. Predicted values were compared with
experimental data. The analytical model was inadequate in predicting
salinisation in a dynamic crop/soil system. When root growth was accounted
for, the numerical model satisfactorily predicted salt increase in the soil profile
A Lanczos algorithm for linear response
An iterative algorithm is presented for solving the RPA equations of linear
response. The method optimally computes the energy-weighted moments of the
strength function, allowing one to match the computational effort to the
intrinsic accuracy of the basic mean-field approximation, avoiding the problem
of solving very large matrices. For local interactions, the computational
effort for the method scales with the number of particles N_p as O(N_p^3).Comment: 12 pages including 3 figures; Late
Models for estimating capillary rise in a heavy clay soil with a saline shallow water table
Shallow saline water tables underlie large areas
of the clay soils in the Murray basin of Australia.
Accurate estimation of capillary rise is important in formulating
management strategies to avoid degradation of
such soils. Measured capillary rise from a saline water
table was compared with capillary rise estimated by three
mathematical models of varying complexity and input
requirement. A quasi steady state analytical model (QSSAM),
a transient state analytical model (TSAM) and a
numerical model (NM) were used. An undisturbed heavy
clay soil core of 0.75 m diameter and 1.4 m deep was
subjected to a static saline water table at 1.2 m from the
surface. A wheat crop was grown on the core and the
weekly capillary rise from the water table was measured.
The electrical conductivity of a 1 : 2 soil : water extract
was determined at 0.15 m depth intervals before and 21
weeks after the introduction of the saline water table. The
QSSAM did not satisfactorily estimate the initial wetting
of the subsoil and the estimated capillary rise was considerably
lower than the measured values. Capillary rise
estimated by the TSAM was reasonably close to the measured
values, but the weekly rates fluctuated considerably.
The NM estimated capillary rise quite satisfactorily
throughout the experiment. Except near the soil surface,
the electrical conductivity values estimated by the NM
were close to the measured values. For estimating total
capillary rise over large areas, the TSAM is preferred
over the NM because of its fewer input requirements and
shorter execution time
Large-Angle Proton-Nucleus Elastic Scattering
This work was supported by the National Science Foundation Grants NSF PHY 78-22774 A03, NSF PHY 81-14339, and by Indiana Universit
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