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  • 1990-1994  (87)
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  • 1
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    PANGAEA
    In:  Supplement to: Meyer, M A; Huang, G-H; Morris, G J; Friedmann, E Imre (1988): 2.2 The effect of low temperatures on Antarctic endolithic green algae. Polarforschung, 58(2/3), 113-119, hdl:10013/epic.29606.d001
    Publication Date: 2023-07-10
    Description: Laboratory experiments show that undercooling to about -5°C occurs in colonized Beacon sandstones of the Ross Desert, Antarctica. High-frequency temperature oscillations between 5°C and -5°C or -10°C (which occur in nature on the rock surface) did not damage Hemichloris antarctica. In a cryomicroscope, H. antarctica appeared to be undamaged after slow or rapid cooling to -50°C. l4CO2 incorporation after freezing to -20°C was unaffected in H. antarctica or in Trebouxia sp. but slightly depressed in Stichococcus sp. (isolated from a less extreme Antarctic habitat). These results suggest that the freezing regime in the Antarctic desert is not injurious to endolithic algae. It is likely that the freezing-point depression inside the rock makes available liquid water for metabolic activity at subzero temperatures. Freezing may occur more frequently on the rock surface and contribute to the abiotic nature of the surface.
    Keywords: Age; Cycles; Range; Standard deviation; Viability
    Type: Dataset
    Format: text/tab-separated-values, 112 data points
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  • 2
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Environmental science & technology 25 (1991), S. 1794-1796 
    ISSN: 1520-5851
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Energy, Environment Protection, Nuclear Power Engineering
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 269-274 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The structure of pseudobinary Co-Zr and Cu-Zr metallic glasses, where Co and Cu were substituted by Fe, was studied by means of 57Fe-Mössbauer spectroscopy. The resulting spectra can be divided into two different classes: (1) For Zr concentrations larger than 67 at. %, the structure of the glass, as derived from Mössbauer spectroscopy, is nearly independent from a substitution, leading to only small changes of the average isomer shifts and quadrupole splittings. These small variations of hyperfine parameters can be ascribed to charge transfer effects. (2) For lower Zr contents, pronounced systematic changes of hyperfine parameters occur upon Co or Cu substitution. Beyond changes of the average hyperfine values, the corresponding quadrupole-splitting distributions become dependent on the degree of substitution, i.e., there is a concentration dependent splitting into two peaks. For the amorphous binary Zr-Fe system, these two peaks have been connected to two amorphous phases with concentrations near Zr2Fe and ZrFe2. At least for the Fe-doped Cu-Zr metallic glasses it could be demonstrated that Fe does not substitute the Cu sites but rather creates preferred environments.
    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 93 (1990), S. 1313-1324 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A molecular dynamics simulation of a realistic model of bicyclo-octane [HC(CH2–CH2)3CH] in its plastic phase has been performed at three different temperatures. The interactions between the molecules of the simulated system are calculated with phenomenological exp-6 additive atom–atom potentials. The molecules are considered rigid and their equations of motion are integrated using a method of constraints. A special attention is given to the problem of the C–H bond value. The static analysis of the molecular dynamics (MD) results yields a clear description of two types of orientational order: It confirms the experimental results about the equipartition of the molecular threefold axes around the eight 〈111〉 crystallographic axes and it furthermore unambiguously shows the existence of six preferred orientations for the orientational order of the molecules around their threefold axes where a previous experimental work concluded in favor of a quasifree rotation. The mean-square displacement amplitudes of the molecular centers of mass reveal that our simulation model is not impeded by the abnormal behavior of the exp-6 potentials at small interactive distances. From a dynamical point of view, the molecular dynamics scheme clearly shows that the jumps are not instantaneous and are slightly more diverse than previously assumed. In order to achieve a precise description of these jumps, we propose to make a conceptual distinction between the mean residence times and the correlation times. By contrast with a former MD simulation, our model gives two sets of distinct characteristic times which perfectly agree with the experimentally deduced values. Given the simplifying assumptions entering the experimental models, the quality of this latter agreement also shows a certain lack of sensitivity vis a¯ vis the exact nature of the underlying microscopic mechanisms. We also examined the ability of our model to simulate the behavior of a monovacancy. We found the influence of such a defect on its immediate neighborhood to be very small even when considering the nature of the complex orientational (dis)order.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 1067-1073 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Molecular dynamics method and Lennard-Jones potential functions are employed to model liquid–liquid interfaces. The simulations are carried out in a range of temperature and pressure near the triple point. The investigated systems are symmetric and composed of two identical liquids L1 and L2. The interactions between the atoms of L1 and L2 are obtained from modified Lennard-Jones potential functions where extra parameters are introduced to reduce the miscibility between the two liquids. The interfacial tensions and the miscibilities are varied by using different parameters. The interfaces thus obtained are stable on the time scale of the simulation as shown by the density and pressure profiles. This is also confirmed by a geometrical analysis performed in order to characterize the fluctuations of the interfaces. The calculation of the diffusion coefficients shows clearly an anisotropy of the diffusion process in the interfacial region.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Environmental science & technology 28 (1994), S. 2267-2277 
    ISSN: 1520-5851
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Energy, Environment Protection, Nuclear Power Engineering
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 53 (1988), S. 1335-1337 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Fine line superconductors of Y-Ba-Cu-O were formed on 〈100〉 SrTiO3 by the completely nonvacuum techniques of metalorganic deposition and selective laser pyrolysis. Lines 35 μm wide were written, using an Ar laser, in metal neodecanoates prior to pyrolysis. Regions of the metalorganics not exposed to laser pyrolysis were developed away using a xylene wash. Complete pyrolysis of the metal neodecanoates and rapid thermal annealing produced lines having superconducting onsets above 90 K and zero resistance at 69 K.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 95 (1991), S. 10723-10729 
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 50 (1994), S. 333-343 
    ISSN: 1600-5740
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Organic solutes, in particular glycine betaine and proline, have been detected as osmoprotective compounds in many microorganisms and herbaceous species. However, for woody plants, very little information is available on mechanisms of adaptation to salt stress. In the present study, effects of NaCI treatment on betaine and free amino acid contents in a clone of Populus trichocarpa X deltoides micropropagated vitroplants were analyzed using HPLC and silicate plate chromatography. The application during 12 days of 50 to 200 mM NaCI to viroplants cultured on Murashige and Skoog medium (Murashige and Skoog 1962. Physiol. Plant. 15: 473–497) led to a progressive decrease of growth, leaf senescence, abscission, and apical necrosis. Populus trichocarpa X deltoides was characterized by the absence of glycine betainc and/or proline accumulation. However, trigonelline was found to increase in vitroplants subjected to 100 mM NaCI. Trigonelline was also present in dormant buds harvested in natural conditions and missing in active buds. In vitroplants, the content of some amino acids was strongly modified by salt stress. A progressive accumulation of alanine and γ-amino butyrate was particularly significant in roots, whereas the relative concentration of glutamine was strongly enhanced in leaves. Leaf content of glutamate and ornithine attained maximum in the presence of 100 and 150 mM NaCI concentrations, and then decreased. Arginine and serine pools were not significantly modified by salt treatment. The variations in vitroplants were of small amplitude compared to those observed in mature poplars where winter rest was associated with a very high arginine level and with a disappearance of nearly all other free amino acids. The results are discussed in relation to previous data obtained with herbaceous species and in relation to some metabolic pathways in poplars where trigonelline could be considered as a sensitive stress indicator.
    Type of Medium: Electronic Resource
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