THE INTRINSIC QUALITATIVE PROPERTIES OF THE CLASSICAL OPTIMAL STOPPING PROBLEM ARE INVARIANT TO THE FUNCTIONAL FORM OF THE DISCOUNT FUNCTION

Abstract The intrinsic qualitative properties of a generic optimal stopping model are shown to be invariant to the functional form of the discount function. If the discount function is assumed to be a member of particular infinite parametric family—a family that includes the exponential and classical hyperbolic discount functions as special cases—an additional refutable comparative statics result is produced that holds for the entire family. Consequently, if one limits econometric tests of the model to its qualitative properties, one cannot determine the form of the discount function used by the decision maker. It is also shown that the only discount function that yields a time‐consistent stopping rule is the exponential function with a constant rate of discount.     

USING NETWORK ANALYSIS TO CHARACTERIZE FOREST STRUCTURE

Abstract Network analysis quantifies different structural properties of systems of interrelated parts using a single analytical framework. Many ecological phenomena have network‐like properties, such as the trophic relationships of food webs, geographic structure of metapopulations, and species interactions in communities. Therefore, our ability to understand and manage such systems may benefit from the use of network‐analysis techniques. But network analysis has not been applied extensively to ecological problems, and its suitability for ecological studies is uncertain. Here, we investigate the ability of network analysis to detect spatial patterns of species association in a tropical forest. We use three common graph‐theoretic measures of network structure to quantify the effect of understory tree size on the spatial association of understory species with trees in the canopy: the node degree distribution (NDD), characteristic path length (CPL), and clustering coefficient (CC). We compute the NDD, CPL, and CC for each of seven size classes of understory trees. For significance testing, we compare the observed values to frequency distributions of each statistic computed from randomized data. We find that the ability of network analysis to distinguish observed patterns from those representing randomized data strongly depends on which aspects of structure are investigated. Analysis of NDD finds no significant difference between random and observed networks. However, analysis of CPL and CC detected nonrandom patterns in three and one of the seven size classes, respectively. Network analysis is a very flexible approach that holds promise for ecological studies, but more research is needed to better understand its advantages and limitations.     

On the Asymptotic Representation of a Regularization Approach to Nonlinear Semiexplicit Higher-Index Differential-Algebraic Equations

Differential-algebraic equations with a higher index can beapproximated by regularization algorithms. One such possibilitywas introduced by März for linear time-varying index 2systems and extended by the author to index 3 systems. In thepresent paper, März’s approach is generalized tononlinear semiexplicit index 2 and 3 equations. The structureof the regularized solutions and their convergence propertiesare characterized in terms of asymptotic expansions.     

MANAGEMENT STRATEGY EVALUATION OF PHEROMONE‐BAITED TRAPPING TECHNIQUES TO IMPROVE MANAGEMENT OF INVASIVE SEA LAMPREY

We applied a management strategy evaluation (MSE) model to examine the potential cost‐effectiveness of using pheromone‐baited trapping along with conventional lampricide treatment to manage invasive sea lamprey. Four pheromone‐baited trapping strategies were modeled: (1) stream activation wherein pheromone was applied to existing traps to achieve 10^?12 mol/L in‐stream concentration, (2) stream activation plus two additional traps downstream with pheromone applied at 2.5 mg/hr (reverse‐intercept approach), (3) trap activation wherein pheromone was applied at 10 mg/hr to existing traps, and (4) trap activation and reverse‐intercept approach. Each new strategy was applied, with remaining funds applied to conventional lampricide control. Simulating deployment of these hybrid strategies on fourteen Lake Michigan streams resulted in increases of 17 and 11% (strategies 1 and 2) and decreases of 4 and 7% (strategies 3 and 4) of the lakewide mean abundance of adult sea lamprey relative to status quo. MSE revealed performance targets for trap efficacy to guide additional research because results indicate that combining lampricides and high efficacy trapping technologies can reduce sea lamprey abundance on average without increasing control costs.     

PHOTOREDUCTION OF METHYLENE BLUE BY WATER*

Abstract— The photoreduction of methylene blue in acid solution has been studied electrochemically. It has been found that methylene blue photoreduction proceeds in red light, with only water available as reducing agent. Reaction energy considerations require two photons to reduce each methylene blue molecule. A two-photon mechanism involving a long-lived dimer intermediate is proposed, and is shown to lead to the observed kinetics, including the dependence of rate on light intensity and methylene blue concentration.     

The onset of thermal runaway in partially insulated or cooled reactors

The conditions for the onset of thermal runaway in partiallyinsulated or cooled reactors are investigated. The temperaturein the reactor is taken to satisfy a nonlinear elliptic equationand the reaction is modelled by an Arrhenius heat generationterm with finite activation energy. To determine the onset ofthermal runaway, the method of matched asymptotic expansionsis used to derive expressions for the critical Frank-Kamenetskiiparameter _c() for reactors containing either a small coolingrod or having a small cooling patch on their boundary. The theoryused to determine _c() is an extension of the results of Wardand Keller (1991). These previous results of Ward and Kellerare also extended to the case of finite activation energiesby using a numerical scheme to evaluate the coefficients inthe asymptotic results for _c(). In some special cases, the asymptoticexpansions for _c() are compared with numerical results for _c(),and clear agreement is found.     

LONG-TERM EFFECTS OF A SINGLE DOSE OF ULTRAVIOLET-B ON ALBINO RABBIT CORNEA-I. in vivo ANALYSES

Both eyes of female albino rabbits (1.9 kg) were exposed to a single dose of UV-B (300 +/- 9 nm; 0.125 J/cm2 total dose) between 13.30 and 15.00 h. The average irradiance was 209 +/- 4 microW/cm2 delivered over 612 +/- 13 s. At various time periods thereafter (every 12 h for 3 days, 6, 7, 14, 28, 42, 56, 112, 224 and 336 days post-irradiation), the animals were subjected to a full slit lamp examination to evaluate the status of the cornea and the anterior segment along with optical or ultrasonic pachometry of central corneal thickness. The results were compared with studies on age-matched rabbits over the same time period. In response to the UV-B irradiation, the corneas showed a modest edema (20% increase in central corneal thickness) that peaked at 48 h. Nearly normal central corneal thickness returned in 6 days and followed by a secondary very slight swelling (less than 5%) that resolved by 14 days. The edema was accompanied by keratitis over the same period. Thereafter, both control and UV-B irradiated corneas progressively increased in thickness with age. Biomicroscopy also revealed the appearance of granular opacities in the corneal epithelium that peaked at 72-96 h and resolved over 28 days. In addition, very small microdot opacities of the corneal epithelium were present in the UV-B irradiated corneas that reached maximum at 72 h but persisted to some degree throughout the evaluation period. Biomicroscopy also revealed a progressive disruption of the homogeneous nature of the corneal stroma by the appearance of large 'bread crumb'-like opacities that started at 72 h and was still present at the end of the evaluation period. These results suggest that long-term evaluation of the cornea is important after acute UV-B exposure and indicate that acute exposure to UV-R can produce corneal changes resembling those reported following chronic exposure to UV-R-rich environments.     

PHOTOCONTROL OF HYPOCOTYL ELONGATION IN LIGHT-GROWN Cucumis sativus L. PHOTOSYNTHETIC REQUIREMENT FOR A FLUENCE RATE DEPENDENT PHYTOCHROME RESPONSE

We investigated the role of photosynthesis in the photocontrol of extension growth of the hypocotyl of light-grown Cucumis sativus L. Previous work [Gaba and Black (1985b) Plant Physiol. 79 , 1011] demonstrated that the inhibition of cucumber hypocotyl elongation is a fluence rate dependent response in red light. However, the relative contributions of phytochrome and photosynthesis to the photon flux dependent inhibition response were not clear. Here we have shown that photoperception by the foliar cotyledons as well as the hypocotyl itself are responsible for fluence rate dependence in red light. The inhibitor of photosynthesis diuron [3-(3,4-dichlorophenyl)-1, 1-dimethylurea] reduced both the magnitude of inhibition and the fluence rate dependency in red light, indicating an involvement of photosynthesis. Furthermore, the growth of non-pigmented seedlings (treated with the herbicide norflurazon) was less inhibited by red light, with no fluence rate dependency. In particular, inhibition due to cotyledon photoperception was completely lost in non-pigmented (norflurazon-treated) plants, and much reduced by diuron treatment. Hypocotyl-perceived red light inhibition was only slightly reduced by treatment with norflurazon and diuron. Photosynthesis was compared directly to photo-inhibition of growth: the photon flux response curve of oxygen evolution of green Cucumis cotyledons was distinctly different from that of hypocotyl inhibition. In conclusion, photosynthesis is an essential requirement for the cotyledon-perceived inhibition, but the response itself is not due to photosynthesis.     

THE PHOTOPHYSICAL PROPERTIES OF SOME C15 LUPINE ALKALOIDS:

Abstract Sparteine, the tetracyclic saturated amine alkaloid, is highly fluorescent in n-hexane solution (Φ_f= 0.64; ζ= 63 ns) and has a large Stokes shift [λ_max (abs) = 203 nm; λ_max (fluor) = 325 nm]. Its isomer, α-isosparteine, has similar properties: Φ_f= 0.55; ζ_f= 50 ns; λ_max (fluor) = 338 nm. Oxidized derivatives, such as lupanine, thermopsine, and α-diplospartyrine, are weakly fluorescent. Based on a comparison with spectroscopic and photophysical properties of the monoamine, quinolizidine, it is concluded that the excitation energy is delocalized over the two N-atoms in starteine and a-isosparteine. The self quenching rate constant for sparteine, ca. 1 times 10⁷M^-1 s^-1, is about 100 times smaller than that for quinolizidine, consistent with excited state derealization. The significant fluorescence quenching in lupanine is rationalized by the fact that N-methyl-2-piperidone mfe/molecularly quenches the fluorescence of quinolizidine at nearly the diffusion controlled rate in -hexane. Comparisons are made with the fluorescence properties of other diamines such as N, N'-dimethylbispidine and N, N'-disubstituted piperazines.