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  • gastrointestinal transit  (2)
  • geostatistics  (2)
  • Springer  (4)
  • 1985-1989  (4)
  • 1955-1959
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  • Springer  (4)
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Year
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical geology 19 (1987), S. 91-98 
    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
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical geology 19 (1987), S. 99-107 
    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
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  • 3
    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
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  • 4
    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
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