Increasing photosynthetic photon flux density (PPFD) received during development from 5.5 to 31.2 mol m-2 d-1 resulted in greater leaf and mesophyll cell surface areas in cotton (Gossypium hirsutum L.). The relationships between the amounts of these surface areas and potential CO2 assimilation by these leaves were evaluated. Leaf area (epidermal surface area of one side of a leaf), mesophyll cell surface area, and net rate of CO2 uptake (Pn) were measured from the time leaves first unfolded until P., was substantially reduced. At the higher PPFD, leaf and mesophyll surface areas increased more rapidly during expansion, and Pn per unit leaf area was greater than at the lower PPFD. Although leaves at the higher PPFD reached the maximum P., per unit mesophyll cell surface area 4 to 5 days earlier than leaves at the lower PPFD, the maxima for these P., were similar. Leaves grown at the higher PPFD had the potential to assimilate 2.2, 3.5, or 5.8 times the amount of CO2 as leaves from the lower PPFD when P., was expressed per unit mesophyll surface, per unit leaf surface, or per whole leaf, respectively. Greater and earlier development of both P., and mesophyll cell surface area at higher PPFD apparently had a compounding effect on the potential for carbon assimilation by a leaf.
Terfenadine is nearly completely first pass biotransformed. Unmetabolized terfenadine plasma concentrations have been associated with altered cardiac repolarization. During previous drug interaction studies, 2 subjects were found to have quantifiable concentrations of unmetabolized terfenadine with accompanying electrocardiographic repolarization changes while on terfenadine alone. To determine whether these subjects were representative of the population, 150 healthy volunteers (109 males, 41 females, ages 19-49) were screened for their ability to metabolize terfenadine after achieving steady-state. Blood was obtained at known times of maximum terfenadine concentration after dosing. Eleven subjects had quantifiable concentrations of terfenadine demonstrating wide intersubject variability in terfenadine metabolism. Further studies to determine whether such subjects are more susceptible to untoward terfenadine-associated events are underway.
Surface‐active solutes (surfactants) can induce capillary pressure gradients and water fluxes within the vadose zone. Common numerical models do not account for the effects of surfactant‐induced capillary pressure gradients on unsaturated flow and transport. We modified the variably saturated flow and transport model HYDRUS‐2D [ Simunek et al. , 1999 ] to incorporate the effects of surfactant concentration‐dependent changes to surface tension and viscosity on moisture retention and hydraulic conductivity, respectively. The model was tested by simulating the two‐dimensional surfactant infiltration experiment of Henry and Smith [2002] . The model successfully captured the major processes associated with the advance of a surface‐active contaminant plume through the vadose zone, including drainage of the vadose zone and depression of the capillary fringe associated with the solute front. The simulations also provided insight into unusual features of surfactant‐induced flow such as the upward flow of surfactant solution that was associated with capillary fringe drainage.
Abstract Air permeability of soil is an important parameter for soil aeration and contaminant remediation techniques such as soil vacuum extraction. Transient‐flow air permeameters are inexpensive and portable, but have been shown to be sensitive to small changes in temperature in the air tank induced by the changing air pressure. We have developed a simple and inexpensive modification to the design of transient‐flow air permeameters that improves both the accuracy and precision of the method. The apparatus was modified by the addition into the air tank of a heat capacitor, i.e., fiberglass insulation. The fiberglass insulation filling the tank acts as a uniformly distributed heat source‐sink (capacitor) and thereby dampens the temperature changes. Data from the near‐isothermal air tank design were compared with data from the standard air tank design and data from a method that uses the standard air tank design but measures both pressure and temperature simultaneously. An air permeability value determined with a steadystate flow method was used as a reference. The results show that nonisothermal air tank data can produce large inaccuracies relative to the steady‐state permeability. Applying a temperature correction to the nonisothermal air tank data improved the results considerably, but this method requires additional temperature and pressure measurements of extreme precision. The permeabilities produced with the “nearly isothermal” air tank closely matched the steady‐state values without having to apply any correction to the data. It is therefore recommended that the air tank of transient air permeameters be filled with a heat capacitor, such as fiberglass insulation.
This article is a summary of the available literature on ocular symptoms due to systemic exposure to mercury. Mercury compounds are first described in terms of their different forms, industrial applications, mechanisms and routes of exposure, toxicity levels, and treatment methods. Eye symptoms are then characterized for organic and inorganic forms of mercury by using the form of various documented case studies of chronic and acute exposure to various mercury compounds.
