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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 69 (1998), S. 3966-3977 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An autofocus circuit, based on measurement of the high spatial frequency image components, was designed for automated microscopic scanning of biological specimens. By careful consideration of the system transfer function, elimination of video end-of-line filter artifacts, correction for illumination instability, and incorporation of autogain, the focus measurement circuit attained the sensitivity and dynamic range necessary for robust operation even at the extremes of biological specimen detail encountered in exhaustive raster scans of thousands of fields. This new circuit exhibited a 25-fold improvement in dynamic range over a previous analog implementation, matched real-time digital performance at an order of magnitude lower cost, resulted in autofocus precision of 56 nm (or 10-fold better than the depth of field of the objective) in scanning experiments comprising over 10 000 microscope fields, and tracked focus at scanning speeds of up to 3.45 fields/s. Focus was correctly maintained in these scanning experiments without additional compensation for low-detail images. This circuit makes possible the widespread inclusion of high-performance autofocus as a low cost option in video microscopy systems. © 1998 American Institute of Physics.
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford UK : Blackwell Science Ltd
    Grass and forage science 53 (1998), S. 0 
    ISSN: 1365-2494
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: The Argentinean semiarid Chaco region is climatically suitable for cattle raising and has an average annual rainfall of 550 mm, concentrated from November to February. There, large areas are affected by high salinity; thus, perennial forages suitable for this region must combine adequate salt and drought tolerance. Panicum coloratum is a C4 perennial grass adapted over a wide range of soil and rainfall conditions, and the purpose of this study was to evaluate the response of two cultivars (Klein Verde and Bambatsi) to salinity. Under controlled conditions, 100 and 200 mmol l−1 NaCl delayed germination and significantly reduced germination percentages and seedling survival in both cultivars. However, in the field, factors other than salinity (possibly drought) had a large impact on plant survival. In short-term experiments under controlled environmental conditions, the vegetative growth of cultivar Klein Verde was less affected by salinity than Bambatsi. The cumulative growth over one year in a saline plot was also higher in cultivar Klein Verde. This cultivar also had higher shoot K+/Na+ ratios under salinity, as a result of higher K+ concentrations, and accumulated more triglycerides in roots. These features have been associated with salt tolerance in other species.
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  • 3
    ISSN: 1748-7692
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 3683-3693 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A method to obtain (approximate) analytical expressions for the radial distribution functions and structure factors in a multi-component mixture of additive hard spheres is introduced. In this method, only contact values of the radial distribution function and the isothermal compressibility are required and thermodynamic consistency is achieved. The approach is simpler than but yields equivalent results to the Generalized Mean Spherical Approximation. Calculations are presented for a binary and a ternary mixture at high density in which the BoublíkMansoori-Carnahan-Starling-Leland equation of state is used. The results are compared with the Percus-Yevick approximation and the most recent simulation data. © 1998 American Institute of Physics.
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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 6814-6819 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A method to obtain (approximate) analytical expressions for the radial distribution functions and structure factors in a multicomponent system of sticky hard spheres is introduced. In its simplest implementation, the method yields the Percus–Yevick approximation. In the next order, only contact values of the cavity functions and the isothermal compressibility are required. Some tentative strategies to determine the input values are discussed. Illustrative examples following these strategies, in which the radial distribution functions and structure factors are computed, are also presented. © 1998 American Institute of Physics.
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  • 6
    Electronic Resource
    Electronic Resource
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 81 (1998), S. 0 
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Available deformation data for superplastic yttria-stabilized zirconia polycrystals with grain size 〈1 µm have been analyzed at temperatures between 1250° and 1450°C as a function of stress, grain size, and impurity content. The apparent stress exponent nfor the higher-purity materials (residual impurity content 〈0.10 wt%) varies from 2 (region II) to greaterthan equal to3 (region I), and then toward 1 when the stress is decreased. The stress for transition between region II and region I decreases when the temperature and/or grain size is increased. The activation energy Qfor flow in region II is 460 kJ/mol, which is approximately that for cation lattice diffusion. The grain-size exponent pdecreases continuously and Qincreases continuously with decreasing stress in region I. The constitutive equation for superplastic flow in region II is identical to that for metallic systems when lattice diffusion is the rate-controlling mechanism. The experimental results have been correlated with a single deformation process that incorporates a threshold stress, below which grain-boundary sliding does not contribute to strain. The threshold stress may result from yttrium segregation at grain boundaries and its interaction with grain-boundary dislocations. A single deformation regime with n= 2 exists for low-purity materials (impurity content 〉0.10 wt%) over the entire stress range. The strain-rate enhancement with respect to high-purity materials is related to the grain-boundary amorphous phase present in such materials.
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  • 7
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Labeling experiments using [1-13C]acetate or [1-13C]glucose were performed with opportunistic pathogenic bacteria, with innocuous bacteria related to pathogenic species or with phytopathogenic species. The labeling pattern was determined in the isoprenic moiety of ubiquinone or menaquinone derivatives. These experiments showed that Acinetobacter, Citrobacter, Erwinia, Pseudomonas, Burkholderia, Ralstonia and Mycobacterium synthesize their isoprenoids via the mevalonate-independent glyceraldehyde 3-phosphate/pyruvate route. Enzymes of this novel bacterial metabolic route, which is apparently absent in vertebrates and man, therefore represent potential targets for a novel type of antibacterial drugs.
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  • 8
    Electronic Resource
    Electronic Resource
    Copenhagen : Munksgaard International Publishers
    Physiologia plantarum 103 (1998), S. 0 
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The role of ABA in freezing resistance in nonacclimated and cold-acclimated barley (Hordeum vulgare L.) was studied. Eleven nonacclimated cultivars differed in their LT50, ranging from −10.8 to −4.8°C. Sugars, free proline, soluble proteins and ABA were analyzed in nonacclimated cultivars and during cold acclimation of one cultivar. There was an inverse correlation between LT50 and both ABA and sucrose contents. Exogenous ABA caused a decrease in the freezing point of leaf tissue in the cultivar with the lowest level of endogenous ABA, but not in the cultivar with the highest level, suggesting that ABA in the latter may be near the optimum endogenous level to induce freezing tolerance. Plants of cv. Aramir treated with ABA or allowed to acclimate to cold temperature increased their soluble sugar content to a similar level. The LT50 of leaves of cold-acclimated cv. Aramir decreased from −5.8 to −11.4°C, with biphasic kinetics, accumulating proline and soluble sugars with similar kinetics. The biphasic profile observed during cold acclimation could be a direct consequence of cryoprotectant accumulation kinetics. ABA and soluble protein accumulation showed a single step profile, associated mainly with the second phase of the LT50 decrease. Thus, a significant increase in endogenous ABA is part of the response of barley to low temperature and may be required as a signal for the second phase of cold acclimation. Endogenous ABA contents in the nonacclimated state may determine constitutive freezing tolerance.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Entomologia experimentalis et applicata 87 (1998), S. 67-72 
    ISSN: 1570-7458
    Keywords: fruit flies ; feeding behavior ; diet nutritional values ; insects ; Diptera ; Tephritidae
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Experiments were carried out to test the performance and some aspects of feeding behavior in two populations of Ceratitis capitata (a population reared in the laboratory for 16 years, i.e., approximately 160 generations, and a wild one obtained from infested coffee, Coffea arabica grains). Two types of food were used in the experiment: an artificial yeast diet used for laboratory rearing and papaya (Carica papaya), a natural host of the fly. The performance parameters tested were percent emergence, time to emergence, adult female size, and egg production during the pre-oviposition phase (first five days of adult life). The behavioral aspects tested were food preference by newly hatched larvae, induction, estimated ingestion of the two diets, whether the larvae placed on one diet stayed there or moved to the other diet, and acceptance of food for oviposition. The results indicated that the performance of the wild population was superior when the flies fed on papaya, whereas the performance of the laboratory population was similar with the two diets; the wild population showed a strong preference for papaya in all choice experiments, whereas the laboratory population showed no diet preference; the females of the wild population only oviposited on pieces of papaya that had not been peeled, and did not oviposit in the artificial diet; the females of the laboratory population oviposited indiscriminately on unpeeled and peeled papaya and on the artificial diet.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Acta biotheoretica 46 (1998), S. 273-297 
    ISSN: 1572-8358
    Keywords: Approximate aggregation ; population dynamics ; time scales ; strong ergodicity ; cyclic environment
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In this work we extend approximate aggregation methods in time discrete linear models to the case of time varying environments. Approximate aggregation consists in describing some features of the dynamics of a general system involving many coupled variables in terms of the dynamics of a reduced system with a few number of variables. We present a time discrete time varying model in which we distinguish two time scales. By using perturbation methods we transform the system to make the global variables appear and build up the aggregated system. The asymptotic relationships between the general and aggregated systems are explored in the cases of a cyclically varying environment and a changing environment in process of stabilization. We show that under quite general conditions the knowledge of the behavior of the aggregated system characterizes that of the general system. The general method is also applied to aggregate a multiregional time dependent Leslie model showing that the aggregated model has demographic rates depending on the equilibrium proportions of individuals in the different patches.
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