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  • Articles  (100)
  • Springer  (100)
  • 1990-1994  (100)
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  • Articles  (100)
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  • 1
    Electronic Resource
    Electronic Resource
    Diffusion-weighted spatial information from1H relaxation in restricted geometries (1992)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 14 (1992), S. 745-759 
    Details
    ISSN: 0392-6737
    Keywords: Nuclear magnetic resonance and relaxation ; Effect of internal magnetic fields ; Biomedical engineering ; diagnostic imaging techniques ; nuclear magnetic resonance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary NMR relaxation of water1H confined in restricted geometries, whatever is the nature of the system (porous media saturated by water as well as biological tissues), exhibits common characteristics. Artificial microporous media saturated by water have been chosen as model systems to study the longitudinal and transverse relaxation of1H magnetization of water molecules diffusing in restricted geometries. These systems are very stable, easy to prepare, with well-characterized pore size distribution and connections, and with highly homogeneous surface properties. The response was compared with that from more complex natural porous media. Scanning Electron Microscopy techniques demonstrated spatial characteristics and surface properties of the samples. The information content of longitudinal relaxation curves associated with spatial structure and due to restricted diffusion is shown in these samples. The effect on transverse relaxation of self-diffusion in the presence of spatially varying magnetic fields due to susceptibility differences is shown. A simple linear relationship has been found in all samples between the transverse relaxation rate and the interpulse delay in CPMG experiments, in spite of the variety of pore shapes and sizes. In general, one can say that relaxation curves beardiffusion-weighted information on the pore space framework. The role of the investigated relaxation mechanisms is important also in the response of biological tissues, including in the presence of MR Imaging contrast agents inducing microscopic magnetic-field gradients.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02451721
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  • 2
    Electronic Resource
    Electronic Resource
    Radiation absorbed by a vertical cylinder in complex outdoor environments under clear sky conditions (1990)
    Springer
    International journal of biometeorology 34 (1990), S. 69-75 
    Details
    ISSN: 1432-1254
    Keywords: Human thermal comfort ; Radiation (absorbed) ; Outdool microclimates ; Human energy budget ; Microclimate simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geography , Physics
    Notes: Abstract Research was conducted into the estimation of radiation absorbed by a vertical cylinder in complex outdoor environments under clear sky conditions. Two methods of estimation were employed: a cylindrical radiation thermometer (CRT) and model developed by Brown and Gillespie (1986), and the weather station model. The CRT produced an integrated temperature reading from which the radiant environment could be estimated successfully given simultaneous measurements of air temperature and wind speed. The CRT estimates compared to the measured radiation gave a correlation coefficient of 0.9499, SE=19.8 W/m2, α=99.9%. The physically-based equations (weather station model)require the inputs of data from a near by weather station and site characteristics to estimate radiation absorbed by a vertical cylinder. The correlation coefficient for the weather station model is 0.9529, SE=16.8 W/m2, α=99.9%. This model estimates short wave and long wave radiation separately; hence, this allowed further comparison to measured values. The short wave radiation was very successfully estimated:R=0.9865, SE=10.0 W/m2, α=99.9%. The long wave radiation estimates were also successful:R=0.8654, SE=15.7 W/m2, and α=99.9%. Though the correlation coefficient and standard error may suggest inaccuracy to the micrometeorologist, these estimation techniques would be extremely useful as predictors of human thermal comfort which is not a precise measure buut defined by a range. The reported methods require little specialized knowledge of micrometeorology and are vehicles for the designers of outdoor spaces to measure accurately the inherent radiant environment of outdoor spaces and provide a measurement technique to simulate or model the effect of various landscape elements on planned environments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01093450
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  • 3
    Electronic Resource
    Electronic Resource
    Immunocytochemical localization of phosphoenolpyruvate carboxylase and photosynthetic gas-exchange characteristics in ears of Triticum durum Desf. (1993)
    Springer
    Planta 191 (1993), S. 507-514 
    Details
    ISSN: 1432-2048
    Keywords: Ear bract ; Kernel ; Phosphoenolpyruvate carboxylase (immunolocalization) ; Photosynthesis ; Triticum (photosynthesis)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The presence and distribution of phosphoenolpyruvate carboxylase (PEPCase) in the glumes and immature grains of durum wheat (Triticum durum Desf.) were studied by electron-microscopical immunolabeling of PEPCase with polyclonal antibodies followed by protein A-gold. Plants were grown under mediterranean field conditions and samples were obtained two weeks after anthesis. In the kernels, high gold label was associated with the unstained areas of the protein bodies of aleurone cells, whereas labeling in the cytoplasm and chloroplasts of the pericarp was slight, although significantly above the background. In the glumes, high gold label was only located in cytoplasmic granules (vesicles) of the mesophyll cells, although labeling in the cytoplasm and chloroplasts was also significantly above the background. These observations in immature kernels and glumes are in accordance with the anaplerotic role of this enzyme, as evidenced in C3 plants. Measurements of apparent photosynthesis and its O2 dependence and CO2 compensation concentration were made on ears and flag leaves of durum wheat. In addition, an analog of phosphoenolpyruvate, 3,3-dichloro-2-dihydroxy-phosphinoylmethyl-2-propenoate, was used to inhibit PEPCase and, thereby, to assess the contribution of the PEPCase to photosynthesis in detached ears. There was no effect of the inhibitor on the apparent photosynthesis of ears. Whereas inhibition of apparent photosynthesis by 210 mL · L−1 O2 in flag leaves was typical of C3 species, inhibition in ears was even greater. The CO2 compensation concentrations in different ear parts were similar to or higher than in flag leaves and the O2 dependence was also comparable (about 70%). Therefore, gas-exchange data give further support to the assumption that a C4 cycle is absent or limited to very low rates in ears of durum wheat.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00195752
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  • 4
    Electronic Resource
    Electronic Resource
    A mixture theory for evaluating heat and mass transport processes in nonhomogeneous snow (1990)
    Springer
    Continuum mechanics and thermodynamics 2 (1990), S. 31-63 
    Details
    ISSN: 1432-0959
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A multiphase mixture theory is developed and then utilized to study heat and mass transport processes in layered snow cover. The material is represented as a granular ice phase and a vapor phase which occupies the pore space. The theory is then implemented to study the process of temperature gradient metamorphism in dry seasonal snow cover and the effect of density layering on metamorphism of snow. Calculated results were found to be consistent with field observations of temperature gradient and density layering effects. The theory demonstrates that sharp variations in density induce a migration of vapor from the lower density snow toward the more dense layer, resulting in a gradual erosion of density of layers adjacent to dense snow. It is also shown that alteration in vapor density and temperature near the layer interface result.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01170954
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  • 5
    Electronic Resource
    Electronic Resource
    Variation of Lyapunov exponents on a strange attractor (1991)
    Springer
    Journal of nonlinear science 1 (1991), S. 175-199 
    Details
    ISSN: 1432-1467
    Keywords: finite time Lyapunov exponents ; strange attractor ; chaos ; predictability ; invariant density
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Physics
    Notes: Summary We introduce the idea of local Lyapunov exponents which govern the way small perturbations to the orbit of a dynamical system grow or contract after afinite number of steps,L, along the orbit. The distributions of these exponents over the attractor is an invariant of the dynamical system; namely, they are independent of the orbit or initial conditions. They tell us the variation of predictability over the attractor. They allow the estimation of extreme excursions of perturbations to an orbit once we know the mean and moments about the mean of these distributions. We show that the variations about the mean of the Lyapunov exponents approach zero asL → ∞ and argue from our numerical work on several chaotic systems that this approach is asL −v. In our examplesv ≈ 0.5–1.0. The exponents themselves approach the familiar Lyapunov spectrum in this same fashion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01209065
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  • 6
    Electronic Resource
    Electronic Resource
    Local Lyapunov exponents computed from observed data (1992)
    Springer
    Journal of nonlinear science 2 (1992), S. 343-365 
    Details
    ISSN: 1432-1467
    Keywords: experimental chaotic time series ; local Lyapunov exponents ; global predictability ; local predictability of chaos
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Physics
    Notes: Summary We develop methods for determining local Lyapunov exponents from observations of a scalar data set. Using average mutual information and the method of false neighbors, we reconstruct a multivariate time series, and then use local polynomial neighborhood-to-neighborhood maps to determine the phase space partial derivatives required to compute Lyapunov exponents. In several examples we demonstrate that the methods allow one to accurately reproduce results determined when the dynamics is known beforehand. We present a new recursive QR decomposition method for finding the eigenvalues of products of matrices when that product is severely ill conditioned, and we give an argument to show that local Lyapunov exponents are ambiguous up to order 1/L in the number of steps due to the choice of coordinate system. Local Lyapunov exponents are the critical element in determining the practical predictability of a chaotic system, so the results here will be of some general use.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01208929
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  • 7
    Electronic Resource
    Electronic Resource
    Cyclic oxidation of Haynes 230 alloy (1992)
    Springer
    Journal of materials science 27 (1992), S. 1514-1520 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The cyclic oxidation of Haynes 230 alloy (Ni-Cr-W-Mo alloy) was investigated in air at three different temperatures, 871, 982 and 1093 °C. Studies indicated that during cyclic oxidation, protective scales formed which were predominantly Cr2O3, with Kirkendall voids formed both at the scale/alloy interface and grain boundaries. Intergranular oxides were observed at temperatures above 982 °C while internal oxide particles were found above 1093 °C. Both intergranular and internal oxides were identified as aluminium oxide. A 50 μm chromium-depleted zone developed after 70 h exposure at 1093 °C and was accompanied by disastrous scale spalling. The lowest chromium concentration within the depleted zone was 14 wt% which still provided a sufficient supply of chromium for development of a continuous Cr2O3 rich scale. Decarburization was observed at the higher temperature of 1093 °C, and a carbide-free zone developed. Also, it was found that Haynes 230 is subject to a sensitization process. At the lower exposure temperature of 871 °C, large amounts of chromium carbide formed preferentially at the grain boundaries. While at the surface region chromium carbide precipitation occurred at the twin boundaries.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00542912
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  • 8
    Electronic Resource
    Electronic Resource
    Roll vortices in the planetary boundary layer: A review (1993)
    Springer
    Boundary layer meteorology 65 (1993), S. 215-248 
    Details
    ISSN: 1573-1472
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Roll vortices may be loosely defined as quasi two-dimensional organized large eddies with their horizontal axis extending through the whole planetary boundary layer (PBL). Their indirect manifestation is most obvious in so-called cloud streets as can be seen in numerous satellite pictures. Although this phenomenon has been known for more than twenty years and has been treated in a review by one of us (R.A.Brown) in 1980, there has been a recent resurgence in interest and information. The interest in ocena/land-atmosphere interactions in the context of climate modeling has led to detailed observational and modeling efforts on this problem. The presence of rolls can have a large impact on flux modelling in the PBL. Hence, we shall review recent advances in our understanding of organized large eddies in the PBL and on their role in vertical transport of momentum, heat, moisture and chemical trace substances within the lowest part of the atmosphere.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00705527
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  • 9
    Electronic Resource
    Electronic Resource
    Cloning and sequencing of the cellulose synthase catalytic subunit gene of Acetobacter xylinum (1990)
    Springer
    Plant molecular biology 15 (1990), S. 673-683 
    Details
    ISSN: 1573-5028
    Keywords: Acetobacter xylinum ; cellulose ; cellulose synthase ; gene cloning ; membrane protein ; UDPG-binding subunit
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The gene for the catalytic subunit of cellulose synthase from Acetobacter xylinum has been cloned by using an oligonucleotide probe designed from the N-terminal amino acid sequence of the catalytic subunit (an 83 kDa polypeptide) of the cellulose synthase purified from trypsin-treated membranes of A. xylinum. The gene was located on a 9.5 kb HindIII fragment of A. xylinum DNA that was cloned in the plasmid pUC18. DNA sequencing of approximately 3 kb of the HindIII fragment led to the identification of an open reading frame of 2169 base pairs coding for a polypeptide of 80 kDa. Fifteen amino acids in the N-terminal region (positions 6 to 20) of the amino acid sequence, deduced from the DNA sequence, match with the N-terminal amino acid sequence obtained for the 83 kDa polypeptide, confirming that the DNA sequence cloned codes for the catalytic subunit of cellulose synthase which transfers glucose from UDP-glucose to the growing glucan chain. Trypsin treatment of membranes during purification of the 83 kDa polypeptide cleaved the first 5 amino acids at the N-terminal end of this polypeptide as observed from the deduced amino acid sequence, and also from sequencing of the 83 kDa polypeptide purified from membranes that were not treated with trypsin. Sequence analysis suggests that the cellulose synthase catalytic subunit is an integral membrane protein with 6 transmembrane segments. There is no signal sequence and it is postulated that the protein is anchored in the membrane at the N-terminal end by a single hydrophobic helix. Two potential N-glycosylation sites are predicted from the sequence analysis, and this is in agreement with the earlier observations that the 83 kDa polypeptide is a glycoprotein [13]. The cloned gene is conserved among a number of A. xylinum strains, as determined by Southern hybridization.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00016118
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  • 10
    Electronic Resource
    Electronic Resource
    Identification of a new gene in an operon for cellulose biosynthesis in Acetobacter xylinum (1991)
    Springer
    Plant molecular biology 16 (1991), S. 947-954 
    Details
    ISSN: 1573-5028
    Keywords: Acetobacter xylinum ; cellulose biosynthesis operon ; cellulose synthase subunit gene ; 93 kDa polypeptide ; membrane protein
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract DNA sequencing of the region downstream of the cellulose synthase catalytic subunit gene of Acetobacter xylinum led to the identification of an open reading frame coding for a polypeptide of 86 kDa. The deduced amino acid sequence of this polypeptide matches from position 27 to 40 with the N-terminal amino acid sequence determined for a 93 kDa polypeptide that copurifies with the cellulose synthase catalytic subunit during purification of cellulose synthase. The cellulose synthase catalytic subunit gene and the gene encoding the 93 kDa polypeptide, along with other genes probably, are organized as an operon for cellulose biosynthesis in which the first gene is the catalytic subunit gene and the second gene codes for the 93 kDa polypeptide. The function of the 93 kDa polypeptide is not clear at present, however it appears to be tightly associated with the cellulose synthase catalytic subunit. Sequence analysis of the polypeptide shows that it is a membrane protein with a signal sequence at the N-terminal end and a transmembrane helix in the C-terminal region for anchoring it into the membrane.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00016067
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