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  • 1
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    In:  EPIC3Deep-sea research part i-oceanographic research papers, 45, pp. 115-131
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
    Format: application/pdf
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 73 (2002), S. 1083-1083 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Following the withdrawal of the U.S. from the International Thermonuclear Experimental Reactor project, the U.S. Fusion Energy Science program has put increased emphasis on plasma science addressing the fundamental scientific issues facing the realization of fusion energy, with decreased emphasis on long-term fusion technology development, except for that which is needed to support near-term experiments. At the same time, the U.S. fusion program has broadened research from the nearly exclusive development of the Tokamak previously, to include now a variety of smaller-scale alternative fusion approaches, including more work on inertial fusion energy (primarily heavy-ion induction accelerators), Spheromaks, Spherical Tori, Stellerators, reversed field pinches, and field-reversed configurations. The largest U.S. Tokamak, the TFTR at PPPL, has been shut down after achieving over 10 MW of DT fusion power, and is now being decommissioned. The powerful TFTR neutral beams, including the ones that injected 120 keV tritium beams, have been decontaminated and stored for possible future use. One of the TFTR beamlines is being used to power the 1 MA National Spherical Torus Experiment (NSTX) located in what was the nearby TFTR hot-cell room. For heavy-ion fusion, the advent of 100 s, 100 TW table-top lasers has increased interest in using field ionization to achieve controlled levels of high-charge-state heavy ions. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 2 (1990), S. 2941-2960 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The physics of enhanced confinement regimes in tokamaks is reviewed and some directions for further enhancements are assessed. The H-mode confinement regime is examined. A number of other observations of enhanced confinement, having in common peaked density profiles, are compared to the theory of ion temperature gradient modes. Two schemes of promise in enhancing confinement, second stability and control of electric fields, are discussed. The contributions of alternate concepts to understanding tokamak transport are described.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Growth and change 26 (1995), S. 0 
    ISSN: 1468-2257
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geography , Economics
    Notes: This paper is a critique of dualistic notions concerning the structure of African economies, and the nature of structural transformation in the region. First, it questions theoretical assumptions that structural transformation in Subsaharan Africa is controlled and directed by market penetration. Second, it argues that, in reality, structural transformation is a process of mutual interaction between the institutions of capital and those of the traditional system. As African individuals, households and communities make deliberate choices about what to optimize and how to undertake the optimization process within given constraints, they choose from traditional and market norms to varying degrees. Finally, it is argued that the outcome of these activities is not a rural-urban dichotomy, but a continuum which reflects different behavioral patterns in economic production and social relationships.
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  • 5
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The influence of the growth photon flux density (PFD) on the size and composition of the carotenoid pool and the size of the reduced ascorbate pool was determined across a light gradient from the forest floor to the canopy and the forest edge of a sub-tropical rainforest in New South Wales, Australia. Nineteen plant species (most collected from multiple sites) representing a broad taxonomic range consistently possessed larger total carotenoid pools when found growing in more exposed sites. There was a significant positive correlation between β-carotene content and growth PFD and a significant negative correlation between α-carotene content and growth PFD. Neoxanthin content exhibited no significant trend while the trend in lutein content varied with mode of expression. The pigments of the xanthophyll cycle (violaxanthin, antheraxanthin and zeaxanthin) exhibited the most pronounced response to growth PFD; they comprised a much greater portion of the total carotenoid pool in high light-acclimated plants. The pool of reduced ascorbate was also several-fold greater in high light-acclimated plants. These acclimatory changes in carotenoid and ascorbate content are consistent with a need for a greater capacity to dissipate excessive absorbed light energy in high light-acclimated plants.
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  • 6
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Leaves of Stephania japonica and Smilax australis were characterized in situ on the coast of north-eastern New South Wales, Australia, where they were growing naturally in three different light environments: deep shade, in the understory of an open Eucalyptus forest where they received frequent sunflecks of high intensity, and in an exposed site receiving full sunlight. In deep shade the xanthophyll cycle remained epoxidized during the day and the vast majority of absorbed light was utilized for photosynthesis. In the exposed site both deepoxidation and epoxidation of the xanthophyll cycle and changes in the level of xanthophyll-dependent thermal energy dissipation largely tracked the diurnal changes in photon flux density (PFD). In the understory the xanthophyll cycle became largely deepoxidized to zeaxanthin and antheraxanthin upon exposure of the leaves to the first high intensity sunfleck and this high level of deepoxidation was maintained throughout the day both during and between subsequent sunflecks. In contrast, thermal energy dissipation activity, and the efficiency of photosystem II, fluctuated rapidly in response to the changes in incident PFD. These findings suggest a fine level of control over the engagement of zeaxanthin and antheraxanthin in energy dissipation activity, presumably through rapid changes in thylakoid acidification, such that they became rapidly engaged for photoprotection during the sunflecks and rapidly disengaged upon return to low light when continued engagement might limit carbon gain.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd, UK
    Plant, cell & environment 21 (1998), S. 0 
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: To assess the possible physiological function of chlorogenic acid (CGA, 3-O-caffeoylquinic acid) in vivo, we characterized the free radical scavenging properties of pure phenylpropanoids and leaf extracts against two free radicals, superoxide and the 2,2’-azinobis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) radical cation. CGA was found to be a highly efficient scavenger of these free radicals, surpassing the activity of all other phenylpropanoids tested, as well as the ‘classical’ antioxidant ascorbate. Seasonal differences in the leaf content of CGA were examined in field populations of the broadleaf evergreen Mahonia repens growing in different light environments. Leaves of fully sun-exposed plants contained significantly more (74 ± 10 mmol m–2) CGA in winter than leaves from plants growing under deeply shaded conditions (17 ± 2 mmol m–2). Sun-acclimated, but not shade-acclimated, leaves also produced high levels of anthocyanins in winter, suggesting a simultaneous increase in carbon flow through the phenylpropanoid and flavonoid pathways in response to high light and seasonal low temperature stress. In summer, high light-acclimated leaves contained ≈ 2-fold less CGA than in winter, whereas CGA levels were similar between seasons in shaded leaves. Consistent with the strong scavenging capacity of CGA measured in vitro, a linear correlation was observed between CGA content and the antioxidant activity of leaf extracts in both scavenging assays. On the basis of these results, we propose that CGA is a powerful hydrogen-donating antioxidant that may play an important role in mitigating the effects of oxidative stress in plants.
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  • 8
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Differently oriented leaves of Yucca schidigera and Yucca brevifolia were characterized in the Mojave Desert with respect to photosystem II and xanthophyll cycle activity during three different seasons, including the hot and dry summer, the relatively cold winter, and the mild spring season. Photosynthetic utilization of a high percentage of the light absorbed in PSII was observed in all leaves only during the spring, whereas very high levels of photoprotective, thermal energy dissipation were employed both in the summer and the winter season in all exposed leaves of both species. Both during the summer and the winter season, when energy dissipation levels were high diurnally, xanthophyll cycle pools (relative to either Chl or other carotenoids) were higher relative to the spring, and a nocturnal retention of high levels of zeaxanthin and antheraxanthin (Z + A) occurred in all exposed leaves of both species. Although this nocturnal retention of Z + A was associated with nocturnal maintenance of a low PSII efficiency (Fv/Fm) on a cold winter night, pre-dawn Fv/Fm was high in (Z + A)-retaining leaves following a warm summer night. This indicates nocturnal engagement of Z + A in a state primed for energy dissipation throughout the cold winter night – while high levels of retained Z + A were not engaged for energy dissipation prior to sunrise on a warm summer morning. Possible mechanisms for a lack of sustained engagement of retained Z + A for energy dissipation at elevated temperatures are discussed.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Marine biology 101 (1989), S. 443-450 
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Blooms of chain-forming diatoms commonly flocculate into centimeter-sized aggregates of living, vegetative cells following nutrient depletion in surface waters off southern California. We examined the hypothesis that diatom cells within aggregates experience increased nutrient uptake relative to unattached cells. We measured in situ settling velocities of 49 to 190 m d−1 and calculated porosities of 0.99931 to 0.99984 (±〉0.03%) for 12, newly-formed diatom flocs ranging from 0.19 to 4.2 cm3 in volume and 7 to 22 mm in equivalent spherical diameter. Using permeability-porosity relationships, we calculated intra-aggregate flow velocities of 20 to 160 μm s−1. Although subject to considerable uncertainty, a Relative Uptake Factor analysis based on mass transfer equqtions suggests that diatoms fixed within aggregates undergoing gravitational settling can take up nutrients up to 2.1±0.4 times faster than unattached diatoms experiencing laminar shear. Increased nutrient uptake by aggregated diatoms may be importan in understanding the reasons for diatom floc formation.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Marine biology 111 (1991), S. 175-181 
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A mass transfer analysis predicts that fluid motion can increase the assimilation of dissolved organics by attached compared to free-living microorganisms under certain conditions. To test this we examined the effect of advective flow and fluid shear on the uptake of model compounds (leucine and glucose) by natural assemblages of heterotrophic bacteria, collected from Roosevelt Inlet, Delaware Bay (USA), in 1989. We found that [3H]leucine uptake by cells held in fluid moving at 20 to 70 m d−1 was eight times larger than uptake by cells at a velocity of 3 m d−1. This effect was only observed at low leucine concentrations (ca. 1 nM), when uptake was likely not saturated. When we added leucine at concentrations expected to saturate leucine uptake (ca. 11 nM), fluid motion past cells did not affect uptake. Fluid flow past bacteria did not increase [3H]glucose uptake, and laminar shear rates of 0.5 to 2.1 s−1 did not increase either glucose or leucine uptake by suspended bacteria. These results indicate that fluid motion increases bacterial uptake of certain lowmolecular-weight dissolved organics only when the microorganism exists in an advective flow field. As predicted from a mass transfer model, fluid shear rates in natural systems are too low to affect bacterial uptake of such compounds.
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