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  • 1995-1999  (2)
Material
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Year
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Communications in mathematical physics 187 (1997), S. 647-677 
    ISSN: 1432-0916
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Physics
    Notes: Abstract: The Hamilton-Jacobi equation describes the dynamics of a hypersurface in . This equation is a nonlinear conservation law and thus has discontinuous solutions. The dependent variable is a surface gradient and the discontinuity is a surface cusp. Here we investigate the intersection of cusp hypersurfaces. These intersections define (n-1)-dimensional Riemann problems for the Hamilton-Jacobi equation. We propose the class of Hamilton-Jacobi equations as a natural higher-dimensional generalization of scalar equations which allow a satisfactory theory of higher-dimensional Riemann problems. The fist main result of this paper is a general framwork for the study of higher-dimensional Riemann problems for Hamilton-Jacobi equations. The purpose of the framwork ist to unterstand the structure of Hamilton-Jacobi wave interactions in an explicit and constructive manner. Specialized to two-dimensional Riemann problems (i.e., the intersection of cusp curves on surfaces embedded in ), this framework provides explicit solutions to a number of cases of interest. We are specifically interested in models of deposition and etching, important processes for the manufacture of semiconductor chips. We also define elementary waves as Riemann solutions which possess a common group velocity. Our second main result, for elementary waves, is a complete characterization in terms of algebraic constraints on the data. When satisfied, these constraints allow a consistently defined closed form expression for the solution. We also give a computable characterization for the admissibility of an elementary wave which is inductive in the codimension of the wave, and which generalizes the classical Oleinik condition for scalar conservation laws in one dimension.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Digestive diseases and sciences 42 (1997), S. 2411-2419 
    ISSN: 1573-2568
    Keywords: GIARDIA ; MOTILITY ; PATHOPHYSIOLOGY ; GIARDIASIS
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract To determine if Giardia lamblia infection isassociated with altered gastrointestinal transit andsmooth muscle contractile function, Mongolian gerbilswere infected orogastrically with 2 ×105 trophozoites (infected) or vehicle (uninfected controls). Atthe time of peak colonization, control and infectedanimals were infused either orogastrically orintraduodenally with 51Cr. Gastric emptyingof isotope and intestinal transit (measured by the geometriccenter of distribution of intestinal 51Crtransit) were significantly (P 〈 0.05) greater in theinfected compared to control animals in both the fastedand the fed states. Then, to determine whether Giardialamblia has an effect on the contractility oflongitudinal and circular smooth muscle, isometrictension of jejunal segments was recorded. Thedevelopment of active tension with stretch and thedose-response curve to bethanechol were significantlyincreased in the longitudinal muscle of infected animalscompared to controls. However, the circular smoothmuscle did not show a similar increase incontractility. These findings suggest that an alteredgastrointestinal transit and smooth muscle contractilitymay be involved in the pathophysiology ofgiardiasis.
    Type of Medium: Electronic Resource
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