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One Surface (one + surface)

Distribution by Scientific Domains

Medical Sciences	40%

Selected Abstracts

Paraxial ray methods for anisotropic inhomogeneous media

GEOPHYSICAL PROSPECTING, Issue 1 2007
Tijmen Jan Moser
ABSTRACT A new formalism of surface-to-surface paraxial matrices allows a very general and flexible formulation of the paraxial ray theory, equally valid in anisotropic and isotropic inhomogeneous layered media. The formalism is based on conventional dynamic ray tracing in Cartesian coordinates along a reference ray. At any user-selected pair of points of the reference ray, a pair of surfaces may be defined. These surfaces may be arbitrarily curved and oriented, and may represent structural interfaces, data recording surfaces, or merely formal surfaces. A newly obtained factorization of the interface propagator matrix allows to transform the conventional 6 × 6 propagator matrix in Cartesian coordinates into a 6 × 6 surface-to-surface paraxial matrix. This matrix defines the transformation of paraxial ray quantities from one surface to another. The redundant non-eikonal and ray-tangent solutions of the dynamic ray-tracing system in Cartesian coordinates can be easily eliminated from the 6 × 6 surface-to-surface paraxial matrix, and it can be reduced to 4 × 4 form. Both the 6 × 6 and 4 × 4 surface-to-surface paraxial matrices satisfy useful properties, particularly the symplecticity. In their 4 × 4 reduced form, they can be used to solve important boundary-value problems of a four-parametric system of paraxial rays, connecting the two surfaces, similarly as the well-known surface-to-surface matrices in isotropic media in ray-centred coordinates. Applications of such boundary-value problems include the two-point eikonal, relative geometrical spreading, Fresnel zones, the design of migration operators, and more. [source]

A three dimensional surface-to-surface projection algorithm for non-coincident domains,

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 6 2003
M. W. Heinstein
Abstract A numerical procedure is outlined to achieve the least squares projection of a finite dimensional representation from one surface to another in three dimensions. Although the applications of such an algorithm are many, the specific problem considered is the mortar tying of dissimilarly meshed grids in large deformation solid mechanics. The algorithm includes a nearest neighbour search, a systematic subdivision of the surface of intersection into smooth subdomains (termed segments), and a robust numerical quadrature scheme for evaluation of the spatial integrals defining the mortar projection. The procedure outlined, while discussed for the mesh tying problem, is directly applicable to the study of contact-impact. Published in 2003 by John Wiley & Sons, Ltd. [source]

Shock-Induced Epicardial and Endocardial Virtual Electrodes Leading to Ventricular Fibrillation via Reentry, Graded Responses, and Transmural Activation

JOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY, Issue 1 2004
FREDERICK G. EVANS Ph.D.
Introduction: The mechanism of ventricular fibrillation (VF) induction by T wave shocks has been attributed to reentry, propagated graded responses (PGR), and triggered activity. The limitation of recording transmembrane potential (Vm) from only a single surface has hampered efforts to elucidate the relative role of these phenomena and their relationship to shock-induced virtual electrodes. Methods and Results:Vm patterns from epicardial and endocardial surfaces of isolated sheep right ventricles were recorded with two CCD cameras for monophasic (M) and biphasic (B) shocks delivered at various coupling intervals (CI) from a unipolar mesh electrode on the epicardium. VF was induced via (1) the formation of reentry following make or break excitation; (2) propagated graded responses during apparent isoelectric window; and (3) breakthrough activation patterns coincident with endocardial-to-epicardial gradients in Vm. M shocks depolarized both surfaces at long CIs and polarized epicardial and endocardial surfaces oppositely at short CIs. At intermediate CIs, postshock Vm patterns could lead to reentry on one surface or endocardial-to-epicardial gradients resulting in breakthrough. B induced VF less than M for short and intermediate CIs due to more homogeneous end-shock Vm patterns. However, at long CIs these homogeneous patterns resulted in more VF induction because B left the tissue closer to the Vm threshold for propagation. Conclusion: Postshock activity occurred either immediately via epicardial or endocardial reentry, or after a delay caused by transmural propagation or propagated graded responses. These findings could explain the isoelectric window and focal activation patterns observed on the epicardium following VF induction shocks. (J Cardiovasc Electrophysiol, Vol. 15, pp. 79-87, January 2004) [source]

Application of Polycaprolactone as an Anti-Adhesion Biomaterial Film

ARTIFICIAL ORGANS, Issue 8 2010
Hsien-Yi Lo
Abstract Adhesions are unavoidable consequences of surgery and other trauma. How to prevent the adhesions remains a big issue in healthcare system. The objective of this study is to test the efficacy of polycaprolactone (PCL) films as physical barriers in reducing postoperative intra-abdominal adhesions in the rat cecum-abdominal wall model. PCL is quite cheap compared with the agents recently used in the market. The fabrication method is also very easy to perform. Scanning electron microscope (SEM) showed multiple pores over upper and bottom surfaces but too small to permit cells to migrate from one surface onto another surface. Those pores were proven to be not interconnected. The PCL film did not show any evidence of cytotoxic effects as it did not induce any significant increase in cytoplasmic lactate dehydrogenase release from the NIH3T3 cells that it came in contact with. In animal studies, the PCL films led to fewer adhesions than Seprafilm in rat adhesion model. PCL films were efficacious in reducing postoperative intra-abdominal adhesion formation in rat cecum-abdominal wall models. [source]

Effect of Thermal Asymmetry on Heat Transfer in a Laminar Annular Flow

CHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 10 2005
J. Mitrovi
Abstract The effect of thermal asymmetry on heat transfer in a hydrodynamically developed annular flow has been investigated numerically. The surfaces confining the fluid space are kept at constant but different temperatures. Depending on the fluid inlet temperature, the thermal asymmetry can lead to a discontinuity of the Nusselt number on one surface. With the thermally developed flow the exact expressions for the Nusselt numbers have been obtained. [source]