806 research outputs found
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
Broadening access to problem-based learning : design of the shell eco-marathon car-in-a-box concept
Abstract: Problem-based learning has proven to develop teamwork, problem solving skills, communication and critical thinking skills amongst learners. Due to these advantages, secondary schools in South Africa engage with problem-based events to promote the participation of learners in Science, Technology, Engineering and Mathematics (STEM). However, many schools face lack of time, lack of available funds and lack of the required technical skill set, which limits them from participating in these events. The Car-In-a-Box concept was developed to broaden access to a STEM problem-based learning event, called the Shell Eco-Marathon. The Car-In-A-Box concept addresses the three challenges that would normally prevent a school from entering the Shell Eco-Marathon, disenabling learners to harness the advantages of problem-based learning. The impact of the Car-In-A-Box concept for broadening access to problem-based learning is discussed
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
Water quality studies of the Delaware River with reference to shad migration
For some time pollution of the waters of the Delaware River by municipal and industrial wastes has been suspected of playing a major role in the decline of the shad fishery. Accordingly, studies were planned to ascertain whether any conditions of water quality caused by stream pollution and harmful or lethal to shad were existant in the waters of the Delaware River during the migration periods of the shad
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
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
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 purely algebraic construction of a gauge and renormalization group invariant scalar glueball operator
This paper presents a complete algebraic proof of the renormalizability of
the gauge invariant operator to all orders of
perturbation theory in pure Yang-Mills gauge theory, whereby working in the
Landau gauge. This renormalization is far from being trivial as mixing occurs
with other gauge variant operators, which we identify explicitly. We
determine the mixing matrix to all orders in perturbation theory by using
only algebraic arguments and consequently we can uncover a renormalization
group invariant by using the anomalous dimension matrix derived from
. We also present a future plan for calculating the mass of the lightest
scalar glueball with the help of the framework we have set up.Comment: 17 page
Feedback-control of quantum systems using continuous state-estimation
We present a formulation of feedback in quantum systems in which the best
estimates of the dynamical variables are obtained continuously from the
measurement record, and fed back to control the system. We apply this method to
the problem of cooling and confining a single quantum degree of freedom, and
compare it to current schemes in which the measurement signal is fed back
directly in the manner usually considered in existing treatments of quantum
feedback. Direct feedback may be combined with feedback by estimation, and the
resulting combination, performed on a linear system, is closely analogous to
classical LQG control theory with residual feedback.Comment: 12 pages, multicol revtex, revised and extende
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