3,024 research outputs found
Recirculating Purging System for Hemispherical Net Radiometers
A purging system was developed to prevent internal
condensation in hemispherical net radiometers without
frequent changing of desiccant. Continuous recirculation
of dry air through the radiometer and a desiccant
tube prevented condensate formation during cool and
wet periods
Automated verification of shape, size and bag properties.
In recent years, separation logic has emerged as a contender for formal reasoning of heap-manipulating imperative programs. Recent works have focused on specialised provers that are mostly based on fixed sets of predicates. To improve expressivity, we have proposed a prover that can automatically handle user-defined predicates. These shape predicates allow programmers to describe a wide range of data structures with their associated size properties. In the current work, we shall enhance this prover by providing support for a new type of constraints, namely bag (multi-set) constraints. With this extension, we can capture the reachable nodes (or values) inside a heap predicate as a bag constraint. Consequently, we are able to prove properties about the actual values stored inside a data structure
Controlled Cooling of Onion Umbels by Periodic Sprinkling
Low onion (Allium cepa L.) seed yields frequently occur
without obvious reasons, particularly with hybrid varieties.
Solutions to the problem need to be found to insure
seed for bulb onion production. Water and temperature
stress in the umbel may be factors during hot,
dry, sunny weather. We investigated the relationship of
umbel temperature to ambient and umbel conditions and
the effects of periodic wetting of the umbels. Onions were
grown in a field experiment at Kimberly, Idaho on Portneuf
silt loam sail (Durixerollic Calciorthids; coarse-silty,
mixed, mesic) using commercial practices except that
periodic sprinkling was provided with a rotating-head
sprinkler irrigation system when temperatures exceeded
certain levels. Sprinkling for five min reduced floret
temperatures as much as 15 C below ambient. The florets
remained cool for 20 to 40 min, depending on umbel maturity,
wind speed, and air temperature and humidity.
Nearly mature umbels were hotter and required more
sprinkling to keep cool. Five min of sprinkling every 20
to 30 min usually provided adequate cooling. A specially-designed
temperature sensor was found to successfully
simulate the behavior of an onion floret during wetting
and drying, permitting direct control of the initiation,
duration, and frequency of sprinkling. Excessive temperatures
did not occur during the experiment, so seed yields
were similar on and unsprinkled plots. While
we have shown that periodic sprinkling will provide umbel
cooling and minimize undesirable effects on pollination,
similar studies need to be conducted in hotter, major
seed producing areas to establish economic benefits
Hazard assessment at Mount Etna using a hybrid lava flow inundation model and satellite-based land classification
International audienceUsing a lava flow emplacement model and a satellite-based land cover classification, we produce a map to allow assessment of the type and quantity of natural, agricultural and urban land cover at risk from lava flow invasion. The first step is to produce lava effusion rate contours, i.e., lines linking distances down a volcano’s flank that a lava flow will likely extend if fed at a given effusion rate from a predetermined vent zone. This involves first identifying a vent mask and then running a downhill flow path model from the edge of every pixel around the vent mask perimeter to the edge of the DEM. To do this, we run a stochastic model whereby the flow path is projected 1,000 times from every pixel around the vent mask perimeter with random noise being added to the DEM with each run so that a slightly different flow path is generated with each run. The FLOWGO lava flow model is then run down each path, at a series of effusion rates, to determine likely run-out distance for channel-fed flow extending down each path. These results are used to plot effusion rate contours. Finally, effusion rate contours are projected onto a land classification map (produced from an ASTER image of Etna) to assess the type and amount of each land cover class falling within each contour. The resulting maps are designed to provide a quick look-up capability to assess the type of land at risk from lava extending from any location at a range of likely effusion rates. For our first (2,000 m) vent zone case used for Etna, we find a total of area of ~680 km2 is at risk from flows fed at 40 m3 s−1, of which ~6 km2 is urban, ~150 km2 is agriculture and ~270 km2 is grass/woodland. The model can also be run for specific cases, where we find that Etna’s 1669 vent location, if active today, would likely inundate almost 11 km2 of urban land, as well as 15.6 km2 of agricultural land, including 9.5 km2 of olive groves and 5.2 km2 of vineyards and fruit/nut orchards
Relationship Between Foliage Temperature and Water Stress in Potatoes
Field studies were conducted in southern Idaho to evaluate the
possibility of using thermal infrared measurements of potato foliage to
detect soil water deficits. Concurrent measurements of foliage-air temperature
differences (Tf-Ta), leaf water potential (?leaf) and vapor pressure
deficit (VPD) were obtained from differentially-irrigated Russet Burbank
and Kennebec potatoes during the 1982 and 1983 growing seasons. Foliage-air
temperature differences for well-watered potatoes were linearly related
to VPD. Differences in Tf-Ta values between stressed and well-watered
potatoes were relatively small in the early morning when evaporative demand
was low. However, severe soil water deficits caused afternoon Tf-Ta
values to rise as much as 8.0 C above non-stressed levels under conditions of
high VPD.
Foliage-air temperature differences and VPD data were used to construct
a plant water stress index (PWSI) which reflected the rise in Tf-Ta,
above non-stressed levels at a given VPD. The PWSI was linearly related to
depressions in ?leaf caused by moderate to severe soil water deficits.
However, the PWSI did not increase significantly above non-stressed values
unless the soil matric potential ?soil fell below – 70 kPa (centibars). Since
potatoes are normally irrigated before ?soil falls below – 60 kPa, it appears
that foliage temperature measurements cannot be used to effectively
schedule irrigation for this crop
Air Temperature and Vapor Pressure Changes Caused by Sprinkler Irrigation
The downwind effect of evaporation from sprinkler
spray was studied in the field to determine if air temperature
and vapor pressure were changed enough to
influence plant growth and water use. Wet-bulb and
dry-bulb temperature profiles were measured upwind
and at three distances downwind from a sprinkler lateral
before and during sprinkling. Wind-speed and direction
were also measured. Air temperature generally was reduced
less than 1 C, and vapor pressure in the air was
increased less than 0.8 mb. This amount of change in
the air temperature and humidity is not likely to be sufficient
to cause any significant change in plant growth or
evaporative loss of water
Response of Plant Water Potential to the Irrigated Environment of Southern Idaho
Laboratory studies have shown that plant water potential
affects a number of key processes involved in
growth, but there has been almost no information on
what levels of water potential occur under irrigated conditions
in the field. Before assessing the practical implication
of laboratory results on soil and crop management,
this type of information must be available. Consequently,
plant water potential in irrigated crops of
Zea mays, Triticum aestivum, Hordeum vulgaris, Phaseolus
vulgaris, Pisum sativum, Solanum tuberosum, Beta
vulgaris, and Medicago sativa, L. was measured throughout
the growing season in southern Idaho. Soil moisture
conditions and potential evapotranspiration were monitored.
Daily changes in plant water potential varied from
less than 5 bars to more than 20 bars, while random sampling
of supposedly homogeneous sets of plants showed
an average variation of about 2 bars. Changes due to
differences in soil moisture were also detected, even
though the soil moisture potential was kept high enough
for near-optimum crop production. Though the crops
differed widely in their response to changes in environment,
the plant water potential was strongly affected by
microclimatic conditions. Day-to-day changes in plant
water potential generally correlated more closely with
changes in potential evapotranspiration than with
changes in soil moisture content. Many of the daily
changes observed in the plants remain unexplained, however.
In general, the average water potential levels of all
the field-grown plants were lower than levels reported
from growth chamber studies. Potentials seldom rose
above —8 bars and were never observed above —5 bars
Photosynthesis Under Field Conditions. IX. Vertical Distribution of Photosynthesis Within a Corn Crop
The vertical distribution of the photosynthetic fixation
of carbon dioxide within a crop of corn was calculated
from carbon dioxide profile data and transfer coefficients
obtained by analysis of windspeed measurements. Infrared
analyzers were used to measure the carbon dioxide
concentration at several heights within and above the
crop. The calculated total fixation for the day was approximately
60 g CO? m-? (equivalent to 470 pounds of sugar
per acre per day). The results demonstrated the importance
of the upper leaves in the fixation of carbon dioxide
and showed the increased fixation by the lower leaves
during periods of high light penetration. There was some
indication that a coupling existed between the level of
windspeed and fixation under conditions of high light
and relatively low windspeed. With refinement in technique
the method could be used to obtain more quantitative
estimates of the distribution of photosynthesis in
other crops
The Energy Budget at the Earth's Surface: Assessing Sources and Sinks of Carbon Dioxide in a Corn Crop Using a Momentum Balance Approach
In two previous communications (Wright and Lemon 1966a, 1966b) an
aerodynamic method was described for evaluating the source and sink
distribution of carbon dioxide in plant communities. Some data were
presented for a corn crop, giving quantitative information about
photosynthetic fixation and respiration release of carbon dioxide, layer
by layer, within the crop.
In the method, CO2 concentration profiles and windspeed measurements of
the bulk air were made within and above the crop. The analysis of the
windspeed measurements to calculate diffusivity coefficients required
tedious analysis of windspeed fluctuations and the application of
complicated statistical and mixing length theories. It is our purpose
to present here a simpler method, requiring vertical profiles of mean
windspeed, vertical profiles of mean carbon dioxide concentration and
representative vertical profiles of the foliage surface area density of
the plant community
Photosynthesis Under Field Conditions. XA. Assessing Sources and Sinks of Carbon Dioxide in a Corn (Zea mays L.) Crop Using Momentum Balance Approach
In a previous communication we described a meteorological
method of assessing the vertical distribution of photosynthesis
and respiration activity in a corn crop. The
method, however, is tedious. Here we describe a much
simpler method. Results indicate that all the leaves of
a corn crop appear to follow the same near-linear light
response curve, at least above the compensation point.
Below the compensation point, all leaves evidently respire
very little
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