Relationship of plant moisture status to irrigation need in corn and soybean crops

Two of the largest problems in irrigation planning are 1) the measurement of crop moisture status and 2) the interpretation of the measurements in terms of irrigation need. This research program was devoted to both these problems and involved the development of a rapid, simple method for measuring crop moisture status that could be used on the individual farm, and the determination of the physiological response of corn and soybean to low moisture availability, As a result, a small, inexpensive pressure chamber was designed, field-tested, and shown to give reasonably accurate values for the moisture status of corn and soybeans. The response of leaf enlargement, photosynthesis, and dark respiration were measured under laboratory conditions in corn, soybean, and sunflower as moisture availability decreased. These data then were used to simulate these processes during a drought that occurred in the field. The simulation showed that, during vegetative development in corn and soybean, leaf enlargement was much more sensitive than photosynthesis or dark respiration to drought. Consequently, irrigation could be based on the maintenance of leaf enlargement alone. Specifically, if pressures measured with the pressure chamber were 30 psi or less at sundown and 2 hours after sunup in leaves normally exposed to full sun, leaf growth, photosynthesis, and dark respiration would be maximal. This relationship did not hold during reproductive growth, however. Chloroplast photosynthesis was studied and was shown to be limiting photosynthesis in sunflower at low moisture availabilities, Effects on the cloroplasts appeared to be largely in the "light” reactions to photosynthesis, where photosystem II, photosystem I, cyclic photophosphorylation, and noncyclic photophosphorylation were inhibited severely. Irrigation after a period of desiccation often brought about complete recovery of the chloroplasts but only incomplete recovery of the stomata, which had been closed prior to irrigation. Studies of liquid water transport showed that soybean had a higher resistance to water movement than did corn or sunflower and that the high resistance was associated primarily with the roots. The root resistance could be kept reasonably low by infecting the roots with mycorrhizal fungi. This work indicates that the moisture status of crops can be simply measured and interpreted at the practical level, and suggests means for irrigation planning which should maximize the efficiency of water use in corn and soybean growing vegetatively.U.S. Geological SurveyU.S. Department of the InteriorOpe

Relationship of crop metabolism and water status to irrigation need

Irrigation represents the largest segment of consumptive water use in the U.S. Consequently, improvements in the efficiency of irrigation can have an important effect on the amount of water available for other uses. This research was initiated to determine the physiological limitations to crop yield during drought. The identification of these parameters may provide a way of estimating plant need for irrigation and avoiding unnecessary applications of water. Maize was grown to maturity, and photosynthesis and translocation of photosynthates were studied when drought occurred during grain development. Both carbon-14 labeling of the photosynthetic products and dry weight determinations indicated that net photosynthesis was substantially reduced whereas translocation was relatively rapid during drought. Furthermore, grain production occurred in proportion to the cumulative photosynthesis for the season. It was concluded that photosynthesis was more limiting than translocation to grain fill under dry conditions and that photosynthetic behavior could be used to reflect the need of maize crops for water.U.S. Geological SurveyU.S. Department of the InteriorOpe

Carbon partitioning and export in transgenic Arabidopsis thaliana with altered capacity for sucrose synthesis grown at low temperature: a role for metabolite transporters

We investigated the role of metabolite transporters in cold acclimation by comparing the responses of wild-type (WT) Arabidopsis thaliana (Heynh.) with that of transgenic plants over-expressing sucrose-phosphate synthase (SPSox) or with that of antisense repression of cytosolic fructose-1,6-bisphosphatase (FBPas). Plants were grown at 23 degrees C and then shifted to 5 degrees C. We compared the leaves shifted to 5 degrees C for 3 and 10 d with new leaves that developed at 5 degrees C with control leaves on plants at 23 degrees C. At 23 degrees C, ectopic expression of SPS resulted in 30% more carbon being fixed per day and an increase in sucrose export from source leaves. This increase in fixation and export was supported by increased expression of the plastidic triose-phosphate transporter AtTPT and, to a lesser extent, the high-affinity Suc transporter AtSUC1. The improved photosynthetic performance of the SPSox plants was maintained after they were shifted to 5 degrees C and this was associated with further increases in AtSUC1 expression but with a strong repression of AtTPT mRNA abundance. Similar responses were shown by WT plants during acclimation to low temperature and this response was attenuated in the low sucrose producing FBPas plants. These data suggest that a key element in recovering flux through carbohydrate metabolism in the cold is to control the partitioning of metabolites between the chloroplast and the cytosol, and Arabidopsis modulates the expression of AtTPT to maintain balanced carbon flow. Arabidopsis also up-regulates the expression of AtSUC1, and to lesser extent AtSUC2, as down-stream components facilitate sucrose transport in leaves that develop at low temperatures.info:eu-repo/semantics/publishedVersio

Photon-Photon and Pomeron-Pomeron Processes in Peripheral Heavy Ion Collisions

We estimate the cross sections for the production of resonances, pion pairs and a central cluster of hadrons in peripheral heavy-ion collisions through two-photon and double-pomeron exchange, at energies that will be available at RHIC and LHC. The effect of the impact parameter in the diffractive reactions is introduced, and imposing the condition for realistic peripheral collisions we verify that in the case of very heavy ions the pomeron-pomeron contribution is indeed smaller than the electromagnetic one. However, they give a non-negligible background in the collision of light ions. This diffractive background will be more important at RHIC than at LHC.Comment: 22 pages, 1 Postscript figures, 4 tables, to appear in Phys. Rev.

Zeta function method and repulsive Casimir forces for an unusual pair of plates at finite temperature

We apply the generalized zeta function method to compute the Casimir energy and pressure between an unusual pair of parallel plates at finite temperature, namely: a perfectly conducting plate and an infinitely permeable one. The high and low temperature limits of these quantities are discussed; relationships between high and low temperature limits are estabkished by means of a modified version of the temperature inversion symmetry.Comment: latex file 9 pages, 3 figure

Calculating Casimir Energies in Renormalizable Quantum Field Theory

Quantum vacuum energy has been known to have observable consequences since 1948 when Casimir calculated the force of attraction between parallel uncharged plates, a phenomenon confirmed experimentally with ever increasing precision. Casimir himself suggested that a similar attractive self-stress existed for a conducting spherical shell, but Boyer obtained a repulsive stress. Other geometries and higher dimensions have been considered over the years. Local effects, and divergences associated with surfaces and edges have been studied by several authors. Quite recently, Graham et al. have re-examined such calculations, using conventional techniques of perturbative quantum field theory to remove divergences, and have suggested that previous self-stress results may be suspect. Here we show that the examples considered in their work are misleading; in particular, it is well-known that in two dimensions a circular boundary has a divergence in the Casimir energy for massless fields, while for general dimension $D$ not equal to an even integer the corresponding Casimir energy arising from massless fields interior and exterior to a hyperspherical shell is finite. It has also long been recognized that the Casimir energy for massive fields is divergent for $D\ne1$. These conclusions are reinforced by a calculation of the relevant leading Feynman diagram in $D$ and three dimensions. There is therefore no doubt of the validity of the conventional finite Casimir calculations.Comment: 25 pages, REVTeX4, 1 ps figure. Revision includes new subsection 4B and Appendix, and other minor correction

Multipartite entangled states in coupled quantum dots and cavity-QED

We investigate the generation of multipartite entangled state in a system of N quantum dots embedded in a microcavity and examine the emergence of genuine multipartite entanglement by three different characterizations of entanglement. At certain times of dynamical evolution one can generate multipartite entangled coherent exciton states or multiqubit $W$ states by initially preparing the cavity field in a superposition of coherent states or the Fock state with one photon, respectively. Finally we study environmental effects on multipartite entanglement generation and find that the decay rate for the entanglement is proportional to the number of excitons.Comment: 9 pages, 4 figures, to appear in Phys. Rev.

On the Verification of Memory Management Mechanisms

We define physical machines as processors with physical memory and swap memory; in user mode physical machines support address translation. We report about the formal verification of a complex processor supporting address translation by means of a memory management unit (MMU). We give a paper and pencil proof that physical machines togethe

Academic freedom: in justification of a universal ideal

This paper examines the justification for, and benefits of, academic freedom to academics, students, universities and the world at large. The paper surveys the development of the concept of academic freedom within Europe, more especially the impact of the reforms at the University of Berlin instigated by Wilhelm von Humboldt. Following from this, the paper examines the reasons why the various facets of academic freedom are important and why the principle should continue to be supported

Is Quantum Mechanics Incompatible with Newton's First Law

Quantum mechanics (QM) clearly violates Newton's First Law of Motion (NFLM) in the quantum domain for one of the simplest problems, yielding an effect in a force-free region much like the Aharonov-Bohm effect. In addition, there is an incompatibility between the predictions of QM in the classical limit, and that of classical mechanics (CM) with respect to NFLM. A general argument is made that such a disparity may be found commonly for a wide variety of quantum predictions in the classical limit. Alternatives to the Schrodinger equation are considered that might avoid this problem. The meaning of the classical limit is examined. Critical views regarding QM by Schrodinger, Bohm, Bell, Clauser, and others are presented to provide a more complete perspective.Comment: Paper has been revised to conform to published versio