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  • Drug delivery  (2)
  • Engineering  (2)
  • Wiley-Blackwell  (4)
  • 1990-1994  (4)
  • 1
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 37 (1994), S. 2935-2950 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The propagation and decay of acoustic waves in exterior domains in an essential ingredient in the study of fluid-structure interaction. A strategy must be devised to compute solutions over domains which are unbounded. Exact impedance conditions at an artificial external boundary are specified by the DtN method, yielding an equivalent problem that is suitable for domain-based computation. The DtN boundary condition is non-reflective, giving rise to exact (and thereby unique) solutions. The truncated DtN operator, which is employed in practice, fails to inhibit the reflection of higher modes, so that non-unique solutions may occur at their harmonics. Simple expressions determine a sufficient number of terms in the truncated operator for unique solutions at any given wave number. There are three characteristic length scales in the computational problem: the radius of the artificial boundary, the geometry of the body (represented by the internal boundary) and the mesh size. Numerical studies examine the dependence of the conditioning of finite element coefficient matrices on the number of terms in the truncated DtN operator vs. the wave number non-dimensionalized by each of the length scales. Analytic results regarding the number of terms sufficient for unique solutions are confirmed. As long as this criterion is respected, no upper limit on the allowable wave number is detected. A local approximation of the boundary conditions restores uniqueness for all wave numbers.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    International Journal for Numerical and Analytical Methods in Geomechanics 17 (1993), S. 659-667 
    ISSN: 0363-9061
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: We present solutions for the effective stress induced by gas flow through a porous solid into a borehole resulting from sudden pressure reduction. Tensile effective stress that exceeds the strength of the solid will lead to borehole failure. This has applications to the intentional creation of cavities, relevant to the efficient recovery of coalbed methane, and the avoidance of borehole stability problems in conventional gas production.
    Additional Material: 3 Ill.
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  • 3
    ISSN: 0170-2041
    Keywords: Amino acids, fatty ; Peptides, lipidic ; Drug delivery ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The α-amino acids with long alkyl side chains, the so-called lipidic amino acids 1a-e, and their homo-oligomers, the lipidic peptides 1p-aj, represent a class of compounds which combine the structural properties of peptides and proteins with the characteristics of lipids and membranes. The amino acids were synthesised from the appropriate alkyl bromide and diethyl acetamidomalonate. Resolution was made chemically, by forming diastereomers of the amino acid esters with an optically pure α-pinene derivative. The protected homooligomers were synthesised in solution with the assistance of a water-soluble carbodiimide coupling agent. In order to modify the physical and chemical properties of the peptides, a series of protected hetero-oligomers were prepared, by similar methods, incorporating either other amino acids (3a - d, 7a - i) or side-chain-substituted lipidic amino acids (6a-d).
    Additional Material: 1 Tab.
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  • 4
    ISSN: 0170-2041
    Keywords: Amino acids, lipidic ; Antibiotics ; Drug delivery ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Lipidic and glyco-lipidic cephalosporin conjugates 1c and 1i were synthesised as diastereomeric mixtures to improve their oral absorption. 2-(tert-Butoxycarbonylamino)tetradecanoic acid was condensed with thiazole 1d and by following basecatalysed hydrolysis of the fully protected rac-1e, the free acid rac-1f was produced. This was then used to acylate the carboxy-protected cephalosporin analog 1g by using a modified Vilsmeier reaction. Removal of the protecting groups of 1b resulted in conjugate 1c. Cephalosporin conjugate li, which contains a sugar moiety in addition to a lipidic amino acid residue, was synthesised to produce a drug conjugate with both lipophilic and hydrophilic properties [radiolabelled (14C) analogs 1a, 1c and 1i were also synthesised]. The radio-labelled parent 1a and conjugates 1c and 1i were administered orally to rats and uptake of the radiolabel in the blood, various organs, urine and faeces was determined. The results showed that an increase in lipophilicity caused an increase in the oral uptake, suggesting that conjugation to lipidic amino acids and peptides is a useful approach to the improvement of the absorption of poorly absorbed drugs.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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