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Fugate K.K.,University Station | Suttle J.C.,University Station | Campbell L.G.,University Station
Postharvest Biology and Technology | Year: 2010

Ethylene elevates respiration, is induced by wounding, and contributes to wound-induced respiration in most postharvest plant products. Ethylene production and its effects on respiration rate, however, have not been determined during storage of sugarbeet (Beta vulgaris L.) root, even though any elevation in respiration due to ethylene would increase storage losses and reduce postharvest quality. To determine the effect of ethylene on sugarbeet root storage respiration rate, sugarbeet root ethylene production was quantified, and the effects of exogenous ethylene, an ethylene biosynthesis inhibitor, and ethylene response inhibitors on root respiration rate were determined using uninjured, severely injured, and conventionally harvested roots. Ethylene production was low (0.045-0.047 pmol kg-1 s-1) in uninjured and conventionally harvested and piled roots. Consequently, ethylene concentrations in commercial piles 0-67 d after piling were low, ranging from <0.001 to 0.054 μL L-1. Exogenous ethylene at concentrations of 0.020-14 μL L-1 increased root respiration. The increase in respiration rate, however, was transient at ethylene concentrations ≤0.11 μL L-1 suggesting that any ethylene effects on respiration rate in commercial piles would be short term. Severe injury induced ethylene production an average of 3.7-fold and increased respiration rate 3-4 d after injury. Wound-induced ethylene production, however, was not directly responsible for wound-induced respiration since elimination of wound-induced ethylene production by the ethylene synthesis inhibitor aminoethoxyvinylglycine had no effect on wound-induced respiration. The ethylene response inhibitors 1-methylcyclopropene (1-MCP) and silver thiosulfate reduced wound-induced respiration 3-4 d after injury when applied after wounding. A portion of the increase in respiration due to wounding, therefore, required ethylene perception. However, when applied prior to wounding, 1-MCP elevated wound-induced respiration 3-4 d after injury, suggesting that blockage of ethylene receptors prior to injury was ineffective at eliminating ethylene perception after wounding, possibly due to the synthesis of new receptors after the injury. Moreover, 1-MCP effects on root respiration rate occurred only when roots were severely injured; 1-MCP had no effect on respiration rate of uninjured or conventionally harvested roots. Postharvest sugarbeet roots, therefore, produce ethylene, increase ethylene production in response to wounding, and respond to exogenous ethylene with an increase in respiration rate, but ethylene production and ethylene effects on root respiration rate are likely to be small under commercial storage conditions and of limited economic significance. Source

Ocampo C.,University of Texas at Austin | Ocampo C.,University Station | Munoz J.-P.,University of Texas at Austin | Munoz J.-P.,University Station
Journal of Guidance, Control, and Dynamics | Year: 2010

Linear perturbation theory is used to develop the variational equations needed to determine the sensitivities of the state at some final time with respect to all of the independent variables associated with a spacecraft trajectory model that is general enough for most applications of interest. The state vector is an augmented vector that includes the position, velocity, mass, and all other control-related variables, such as thrust magnitude and direction. The force model is general and the trajectory can have any number of impulsive and/or finite burn maneuvers. The gradient expressions depend, in part, on the system state transition matrix associated with the given state and its corresponding equations of motion. As an example, the procedure developed is applied to the numerical optimization of a multi-impulse escape trajectory from the moon. Copyright © 2010 by the American Institute of Aeronautics and Astronautics, Inc. Source

Rios Perez C.A.,University of Texas at Austin | Rios Perez C.A.,University Station | Lowrey J.D.,University of Texas at Austin | Lowrey J.D.,University Station | And 3 more authors.
Journal of Radioanalytical and Nuclear Chemistry | Year: 2012

Developing a better understanding of xenon transport through porous systems is critical to predicting how this gas will enter the atmosphere after a below ground nuclear weapons test. Radioxenon monitoring is a vital part of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) International Monitoring System. This work details the development of prompt gamma activation analysis for measuring the diffusion rates of xenon and argon gases through a porous medium. The University of Texas at Austin maintains a prompt gamma activation analysis facility with a peak neutron flux of ∼1.5 × 107 cm-2 s-1 and a beam diameter of 1 cm. Due to the relatively large prompt gamma cross sections of many stable xenon isotopes at thermal and sub-thermal neutron energies, prompt gamma activation analysis is a suitable technique for in situ non-destructive analysis of natural xenon. A test chamber has been designed and constructed to utilize prompt gamma activation analysis to measure xenon and argon diffusion through geological materials (e.g., sand, soil, etc.). Initial experiments have been conducted to determine the detection limits for stable gas measurements. The results from these experiments will be utilized to benchmark parts of a xenon transport model that is being used to determine diffusion coefficients for xenon and argon. © Akadémiai Kiadó, Budapest, Hungary 2011. Source

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