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  • Rhus  (2)
  • gastrointestinal transit  (2)
  • geostatistics  (2)
  • Springer  (6)
  • 1985-1989  (6)
  • 1955-1959
Collection
Keywords
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  • Springer  (6)
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Year
  • 1
    Electronic Resource
    Electronic Resource
    Recovery patterns of three chaparral shrub species after wildfire (1989)
    Springer
    Oecologia 80 (1989), S. 309-320 
    Details
    ISSN: 1432-1939
    Keywords: Chaparral ; Seedling survival ; Root depth ; Rhus ; Ceanothus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary In a mature, even aged stand of mixed chaparral, Rhus laurina (facultative resprouter) had consistently higher water potentials and deeper roots than Ceanothus spinosus (facultative resprouter) and Ceanothus megacarpus (obligate seeder). For two years following a wildfire, the same stand of chaparral had resprouts with higher survivorships, predawn water potentials, stomatal conductances, photosynthetic rates and shoot elongation rates than seedlings. Supplemental irrigation of seedlings during summer months removed differences between resprouts and seedlings suggesting that the cause of such differences was limited water availability to the shoot tissues of seedlings. After two years of postfire regrowth, mean seedling survivorship for the obligate seeder (C. megacarpus) was 42%, whereas seedling survivorship for facultative resprouters was only 18% (C. spinosus) and 0.01% (R. laurina). Our results are consistent with the hypothesis that lack of resprouting ability among obligate seeders is offset by an enhanced ability to establish seedlings after wildfire, allowing obligate seeders to maintain themselves in mixed populations through many fire cycles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00379032
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  • 2
    Electronic Resource
    Electronic Resource
    Comparative physiology of burned and unburned Rhus laurina after chaparral wildfire (1986)
    Springer
    Oecologia 71 (1986), S. 63-68 
    Details
    ISSN: 1432-1939
    Keywords: Rhus ; Lignotuber ; Nitrogen ; Water relations ; Fire
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Laurel Sumac (Rhus laurina) is a dominant member of the coastal chaparral community of southern California that survives periodic burning by wildfires by resprouting from a lignotuber (root crown). We investigated the physiological basis for resprouting by comparing shoot elongation, leaf nitrogen content, tissue water status, leaf conductance to water vapor diffusion, and photosynthetic rates of post-fire R. laurina to those of adjacent unburned shrubs. Resprouts had higher rates of shoot elongation, leaf conductance, and photosynthesis than mature, unburned shrubs. Leaf nitrogen contents were elevated in burned shrubs even though their leaves developed interveinal chlorosis. A comparison of soil water potential to predawn water potential indicated that roots of R. laurina remain active below 2 m during the first summer drought after wildfire. Our results support the hypothesis that lignotubers not only contain dormant buds that develop into aerial shoots after wildfire but they also supply nutrient resources that enhance shoot elongation. Because R. laurina is relatively sensitive to drought, yet very successful in its rapid recovery after fire, maintaining an active root system after shoot removal may be the primary function of the massive lignotuber formed by this species.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00377322
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  • 3
    Electronic Resource
    Electronic Resource
    Production of conditional simulations via the LU triangular decomposition of the covariance matrix (1987)
    Springer
    Mathematical geology 19 (1987), S. 91-98 
    Details
    ISSN: 1573-8868
    Keywords: geostatistics ; kriging ; conditional simulation ; fast Fourier transform
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract This paper reviews the turning band method and fast Fourier transform method of producing a nonconditional simulation of a multinormal random function with a given covariance structure. A review of the two common methods of conditioning the simulation to honor the data shows that they are formally equivalent. Another method for directly pondering a conditional simulation based on the LU triangular decomposition of the covariance matrix is presented. Computational and implementation difficulties are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00898189
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  • 4
    Electronic Resource
    Electronic Resource
    Generating large stochastic simulations—The matrix polynomial approximation method (1987)
    Springer
    Mathematical geology 19 (1987), S. 99-107 
    Details
    ISSN: 1573-8868
    Keywords: geostatistics ; simulation ; Toeplitz matrices ; block Toeplitz matrices ; matrix polynomial approximation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract An algorithm for producing a nonconditional simulation by multiplying the square root of the covariance matrix by a random vector is described. First, the square root of a matrix (or a function of a matrix in general) is defined. The square root of the matrix can be approximated by a minimax matrix polynomial. The block Toeplitz structure of the covariance matrix is used to minimize storage. Finally, multiplication of the block Toeplitz matrix by the random vector can be evaluated as a convolution using the fast Fourier transform. This results in an algorithm which is not only efficient in terms of storage and computation but also easy to implement.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00898190
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  • 5
    Electronic Resource
    Electronic Resource
    The effect of density on the gastric emptying of single- and multiple-unit dosage forms (1986)
    Springer
    Pharmaceutical research 3 (1986), S. 208-213 
    Details
    ISSN: 1573-904X
    Keywords: gastrointestinal transit ; pellet density ; floating formulations, gastric emptying
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The gastric emptying of pellets and single units of different densities has been followed in healthy subjects using the technique of gamma scintigraphy. The gastric emptying of the light pellets was affected by their buoyancy in the upper part of the stomach. However, the mean gastric emptying rates of pellets and single units were not significantly affected by density. Floating or buoyant delivery systems may have little advantage over conventional systems. The presence of food in the stomach was found to be the major factor in determining the gastric emptying of single units.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1016334629169
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  • 6
    Electronic Resource
    Electronic Resource
    Correlation of Phenylpropanolamine Bioavailability with Gastrointestinal Transit by Scintigraphic Monitoring of 111In-Labeled Hydroxypropylmethylcellulose Matrices (1989)
    Springer
    Pharmaceutical research 6 (1989), S. 274-278 
    Details
    ISSN: 1573-904X
    Keywords: bioavailability ; scintigraphy ; gastrointestinal transit ; controlled release ; phenylpropanolamine ; hydroxypropylmethylcellulose
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Two controlled-release hydroxypropylmethylcellulose (HPMC) matrix formulations, a single-unit and a multiple-unit system, have been evaluated in human volunteers. Both formulations contained the sympathomimetic drug phenylpropanolamine hydrochloride and each was radiolabeled with 111Inbound Amberlite IR 120 ion-exchange resin. The formulations were administered to each of six healthy male volunteers and gastrointestinal (GI) transit was monitored using a gamma camera. Serum samples were taken at set time intervals and assayed for phenylpropanolamine content, thus allowing blood drug levels to be correlated with the position of the dosage form in the GI tract. The multiple-unit system emptied from the stomach gradually over a period of about 180 min, when administered after a light breakfast, whereas the single-unit dosage forms had extremely variable gastric emptying times (range, 60 to 〉570 min). However, both formulations provided prolonged phenylpropanolamine blood levels. The differences in the blood profiles obtained with the two formulations were attributed to variations in their in vitro release rates and not to any differences in their GI transit times.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1015986121822
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