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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 777 (1996), S. 0 
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Notes: Although many cognitive functions are affected by age, some are relatively maintained. There also are numerous age-related changes in brain structure, but not much is known about how these changes impact upon the alterations seen in cognition. In order to understand the basis for the reductions and sparings of cognitive function in the aged, experiments were carried out to compare regional cerebral blood flow (rCBF) and performance in young and old subjects on visual perceptual and memory tasks. In the first experiment, which examined the perception of faces and spatial locations, old subjects were as accurate as young subjects, and both groups had rCBF activation in fusiform gyrus during face matching and in superior parietal cortex during location matching. However, old subjects had less activation of prestriate cortex and more activation of frontal and lateral temporal cortex than did young subjects. The second experiment tested recognition memory for faces, a task on which old subjects were impaired. Young subjects had rCBF activation in left prefrontal and inferior temporal cortex and in right hippocampus during encoding of the faces, and in right prefrontal and parietal cortex during recognition. Old subjects showed no significant activation of the areas involved in encoding, but did have increased rCBF in right prefrontal cortex during recognition. These results suggest that the aging brain can demonstrate alterations of the functional systems involved in some cognitive processes, such as perception, that may serve as a compensatory mechanism to maintain performance. Failure to show such compensation, coupled with dysfunction of the areas primarily involved in processing may lead to more marked deficits in performance.
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  • 2
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Industrial and engineering chemistry 15 (1976), S. 228-229 
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Industrial and engineering chemistry 13 (1974), S. 341-346 
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Astrophysics and space science 212 (1994), S. 107-114 
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We present archival and recent IUE high dispersion spectra of late B stars which reveal the presence of accreting gas with velocities as high as 350 km s−1, collisional ionization of the accreting gas to temperatures above the stellar Teff, and column densities intermediate between those observed toward classical Herbig Ae/Be stars and the nearby proto-planetary systemβ Pictoris. One of the stars, HD 176386, while lacking obvious optical signatures of youth, is a member of the R CrA star formation region, and with an inferred age of 2.8 Myr has not yet arrived on the zero-age main sequence (ZAMS). The other object, an isolated, field B star with pronounced IR excess due to warm, circumstellar dust, 51 Oph, exhibits only modest hα emission. The combination of high velocity, accreting gas in systems with IR excesses due to circumstellar dust suggests that not only are these objects candidate proto-planetary systems, but that they may represent an extension to higher stellar masses of the weak-emission pre-main sequence (PMS) stars.
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Astrophysics and space science 212 (1994), S. 115-124 
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Analysis of IUE high- and low-dispersion spectra of the young Herbig Ae star HR 5999 (HD 144668) covering 1978–1992 has revealed dramatic changes in the Mg II h and k (2795.5, 2802.7 Å) emission profiles, changes in the column density and distribution in radial velocity of accreting gas, and flux in the Lyα, OI and CIV emission lines, which are correlated with the UV excess luminosity. We also observe variability in the spectral type inferred from the UV spectral energy distribution, ranging from A5 IV-III in high state to A7 III in the low state. The trend of earlier inferred spectral type with decreasing wavelength and with increasing UV continuum flux has previously been noted as a signature of accretion disks in lower mass pre-main sequence stars (PMS) and in systems undergoing FU Orionis-type outbursts. Our data represent the first detection of similar phenomena in an intermediate mass (M ≥ 2M ⊙) PMS star. Recent IUE spectra show gas accreting toward the star with velocities as high as +300 km s−1, much as is seen towardβ Pic, and suggest that we also view this system through the debris disk. The absence of UV lines with the rotational broadening expected given the optical data (A7 IV,v sini = 180 ± 20 km s−1) for this system also suggests that most of the UV light originates in the disk, even in the low continuum state. The dramatic variability in the column density of accreting gas, consistent with clumpy accretion, such as has been observed towardβ Pic, is a hallmark of accretion onto young stars, and is not restricted to the clearing phase, since detectable amounts of accretion are present for stars with 0.5 〈t age 〈 2.8 Myr. The implications for models ofβ Pic and similar systems are briefly discussed.
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  • 6
    ISSN: 1572-9729
    Keywords: 2-chlorophenol ; continuous culture ; L-lysine ; mixed microbial community ; multicomponent substrate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Continuous culture experiments with identical experimental designs were run with a mixed microbial community of activated sludge origin and an axenic bacterial culture derived from it. Each culture received 2-chlorophenol (2-CP) at a concentration of 160 mg/L as COD and L-lysine at a concentration of 65 mg/L as COD. A factorial experimental design was employed with dilution rate and media composition as the two controlled variables. Three dilution rates were studied: 0.015, 0.0325, and 0.05 h−1. Media composition was changed by adding four biogenic compounds (butyric acid, thymine, glutamic acid and lactose) in equal COD proportions at total concentrations of 0, 34, 225, and 1462 mg/L as COD. The measured variables were the effluent concentrations of 2-CP as measured by the 4-aminoantipyrene test and lysine as measured by the o-diacetylbenzene procedure. The results suggest that community structure and substrate composition play important roles in the response of a microbial community to mixed substrates. The addition of more biogenic substrates to the axenic culture had a deleterious effect on the removal of both lysine and 2-CP, although the effect was much larger on lysine removal. In contrast, additional substrates had a positive effect on the removal of 2-CP by the mixed community and much less of a negative effect on the removal of lysine. The dilution rate at which the cultures were growing had relatively little impact on the responses to the additional substrates.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Water, air & soil pollution 123 (2000), S. 117-132 
    ISSN: 1573-2932
    Keywords: biological nutrient removal ; ecological engineering ; filamentous bulking ; glycogen accumulating organisms ; nitrifying bacteria ; phosphorus accumulating organisms
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract Biological nutrient removal (BNR) systems remove carbon, nitrogen, and phosphorus from wastewaters through biodegradation of organic compounds, oxidation of ammonia-N to nitrate-N, reduction of nitrate-N to N2 gas, and sequestration of phosphorus as polyphosphate. The microbial community in such systems is complex because it must contain heterotrophic bacteria capable of aerobic respiration, anaerobic respiration, and fermentation; specialized heterotrophic bacteria that can store polyphosphate; and autotrophic nitrifying bacteria that can withstand long periods without oxygen. Although the basic design principles for BNR systems are reasonably well established, it is becoming apparent that a greater understanding of the microbial interactions involved is required to increase system reliability. For example, although the environment established for the selection of phosphorus accumulating organisms was thought to give them a strong competitive advantage over other heterotrophic bacteria, this has turned out not to be the case. Rather, glycogen accumulating organisms can compete quite effectively in the same environment. Furthermore, BNR systems have suffered from problems with sludge settleability, even though many of the system characteristics are considered to be conducive to the suppression of filamentous bacteria. Finally, the use of molecular techniques has revealed that the autotrophic nitrifying bacteria are different from those that had been considered to be present. This paper reviews the microbial ecology of BNR systems, establishes how molecular biology techniques are changing our understanding of that ecology, and suggests ways in which engineering control can be exerted over community structure, thereby increasing the reliability of BNR systems.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 17 (1975), S. 859-872 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A natural microbial population of sewage origin was grown at four temperatures (10, 20, 30, 40°C) and five mean residence times (3, 6, 12, 18, 24 hr) in a continuous stirred tank reactor. Samples of cells were removed during steady-state operation and analyzed for chemical oxygen demand (COD), ash content, protein, carbohydrate, and nucleic acids. The oxygen equivalence (OE) of the cells was measured directly as g COD/g ash-free cells and was determined indirectly by calculating the calorific content from the macromolecular composition. The results indicate that OE is a function of growth conditions. Furthermore the COD test is a poor measureof OE because of a high level of variation associated with the test. Additional studies should be performed using bomb calorimetry to establish a quantitative relationship between growth conditions and OE.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 24 (1982), S. 1427-1444 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The RNA-limiting theory of transient response states that the primary physiological adaptation which occurs when microbial cultures are grown at specific rates less than their maximum is a decrease in the cellular level of RNA. It predicts that, as a result of this decrease, the response of the culture to a shift-up in growth rate will be limited by its RNA level. In order to test the RNA-limiting theory and to investigate the role physiological adaptation in transient response, experiments were performed in which steady-state chemostat cultures of Pseudomonasputida grown at various specific rates were transferred to batch reactors containing sufficient carbon source (L-lysine) and nutrients to remove all external growth restrictions. Samples were collected during the subsequent transient period for determination of the macromolecular composition and the maximum instantaneous oxygen uptake rate. The results indicated that, while decreases in the RNA level did significantly affect the nature of the transient response, other unidentified components varied with the steady-state specific growth rate at which the culture had been grown prior to the shift-up and that the levels of those components affected the nature of the subsequent transient response. This implies that the RNA-limiting theory is inadequate for describing the transient responses of cultures grown over a wide range of specific growth rates.
    Additional Material: 7 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 14 (1972), S. 391-410 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Studies were performed using pure cultures of A. acrogenes and E. coli and a heterogeneous microbial population growing in carbon-limited chemostats with glucose as the sole carbon and energy source. A two-level factorial experimental design was employed to test the hypothesis that the concentration of growth-limiting substrate in a chemostat is controlled by the growth rate alone and is independent of the concentration of substrate entering the reactor. The pure culture experiments showed that the conclusions depend upon the measurement employed for growth-limiting substrate. When the concentration of glucose was measured directly, the hypothesis was found to be true within the limits of the study (500-1500 mg/liter). However, if the chemical oxygen demand (COD) test was used as the measure of growth-limiting substrate the hypothesis was found to be false. When heterogeneous cultures were employed the hypothesis was false regardless of the technique used to measure the concentration of growth-limiting substrate. Nevertheless, it was possible to generate regression equations which described the interactions among influent COD, growth rate, and effluent COD with a high level of correlation.
    Additional Material: 6 Ill.
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