bar of osmotic pressure were, respectively, 0.576 +0.004, 0.570+0.004, 0.568 +0.004, and 0.562 ? 0.005. These sensitivity values for the separate couples are averages for determinations at five osniotic pressures. The standard errors measure the accuracy of proportionality between output, in microvolts, and osmotic pressure. The coefficient of variability of the voltage readings for five replicates of each of the KCl concentrations was determined for each of the thermocouples; the over-all average of these 20 coefficients was 0.5 percent. The highest variability occurred at the highest osmotic pressure for which the average coefficient of variability for the four junctions was 1.1 percent.The calibration of a hygrometer that makes use of evaporative cooling depends on atmospheric pressure. For a given osmotic solution in the sample chamber of the couples here described, the rate of change of sensitivity with change in atmospheric pressure is constant but increases as the osmotic pressure of the sample is increased. The increase in sensitivity for a 10-mbar decrease in barometric pressure is 0.00145, 0.00155, and 0.00160 %v, respectively, per bar of osmotic pressure, for standard osmotic solutions of 5, 10, and 20 bars. Correction for change of atmospheric pressure from the value at calibration will not often be needed, but barometer readings should be taken so that correction can be made if necessary.The physical condition of water in soil is usually specified in terms of equivalent membrane pressures, largely because measuring techniques employing membranes are available. With thermocouples which can be accurately calibrated in terms of relative pressure near saturation, it seems clear that the thermodynamic functions of free energy and activity will be more generally used for describing soil-water-plant systems.
Reducing stress on livestock during handling will help reduce sickness and enable cattle to go back on feed more quickly. Many detrimental effects of handling stressors on animal performance and health are likely due to fear. Practical experience on ranches and feedlots shows that making cattle accustomed to people both on foot and on horseback will produce calmer and easier to handle cattle. An animal's first experience with a new corral, a person, or pieces of equipment should be made as positive as possible. If a painful or very aversive procedure is done the first time, it may be difficult to persuade the animal to re-enter the facility. The following tips will improve handling: move small numbers of animals at a time, do not overload the crowd pen, eliminate electric prods, open anti-back gates, eliminate visual distractions that make animals balk, use flight zone and point of balance principles, and reduce noise.
The nutritionally important trace elements share a high biological activity, implemented through association with enzymes, hormones or vitamins. The same activity responsible for physiological responses at extremely low dietary levels implies the potential for metabolic upset when the elements are ingested at elevated, although still relatively low levels. Selenium provides a classic example of this dichotomy of effects and has generated concerns at both ends of its supply spectrum. Experiences in the Dakotas, mid-19th century, led to identification of toxicity symptoms for which selenium was later shown to be responsible, while separate studies showed that excess selenium was teratogenic in the developing avian fetus. These toxic reactions suggested that selenium might be useful in restricting abnormal cell growth, and recent studies have proved it to be anticarcinogenic in certain specific circumstances. Investigation of selenium's nutrient function has been equally interesting, and when Schwarz showed it to be an essential nutrient in 1957, he began an era of intense research activity. Dietary levels of selenium below 0.02 ppm were found to cause deficiency symptoms affecting muscles, liver and pancreas and glutathione peroxidase was shown to be an active form through which selenium acted to prevent such aberrations. Research continues to seek other active organic combinations for selenium to identify interfering compounds that restrict its bioactivity and to explore biochemical mechanisms involved in its toxicity.
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