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Uniform Way (uniform + way)

Distribution by Scientific Domains
Medical Sciences40%
Engineering40%

Selected Abstracts

Non-locking tetrahedral finite element for surgical simulation

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 7 2009
Grand Roman Joldes
Abstract To obtain a very fast solution for finite element models used in surgical simulations, low-order elements, such as the linear tetrahedron or the linear under-integrated hexahedron, must be used. Automatic hexahedral mesh generation for complex geometries remains a challenging problem, and therefore tetrahedral or mixed meshes are often necessary. Unfortunately, the standard formulation of the linear tetrahedral element exhibits volumetric locking in case of almost incompressible materials. In this paper, we extend the average nodal pressure (ANP) tetrahedral element proposed by Bonet and Burton for a better handling of multiple material interfaces. The new formulation can handle multiple materials in a uniform way with better accuracy, while requiring only a small additional computation effort. We discuss some implementation issues and show how easy an existing Total Lagrangian Explicit Dynamics algorithm can be modified in order to support the new element formulation. The performance evaluation of the new element shows the clear improvement in reaction forces and displacements predictions compared with the ANP element in case of models consisting of multiple materials. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Noncompartmental kinetic analysis of DCE-MRI data from malignant tumors: Application to glioblastoma treated with bevacizumab

MAGNETIC RESONANCE IN MEDICINE, Issue 2 2010
Ruediger E. Port
Abstract Dynamic contrast enhanced MRI contrast agent kinetics in malignant tumors are typically complex, requiring multicompartment tumor models for adequate description. For consistent comparisons among tumors or among successive studies of the same tumor, we propose to estimate the total contrast agent,accessible volume fraction of tumor, including blood plasma, vpe, and an average transfer rate constant across all tumor compartments, Ktrans.av, by fitting a three-compartment tumor model and then calculating the area under the tumor impulse-response function (= vpe) and the ratio area under the tumor impulse response function over mean residence time in tumor (= Ktrans.av). If the duration of dynamic contrast enhanced MRI was too short to extrapolate the tumor impulse-response function to infinity with any confidence, then conditional parameters v and Ktrans.av* should be calculated from the available incomplete impulse response function. Median decreases of 33% were found for both v and Ktrans.av* in glioblastoma patients (n = 16) 24 hours after the administration of bevacizumab (P < 0.001). Median total contrast-enhancing tumor volume was reduced by 18% (P < 0.0001). The combined changes of tumor volume, v, and Ktrans.av* suggest a reduction of true vpe, possibly accompanied by a reduction of true Ktrans.av. The proposed method provides estimates of a scale and a shape parameter to describe contrast agent kinetics of varying complexity in a uniform way. Magn Reson Med, 2010. © 2010 Wiley-Liss, Inc. [source]

Categorical abstract algebraic logic: The criterion for deductive equivalence

MLQ- MATHEMATICAL LOGIC QUARTERLY, Issue 4 2003
George Voutsadakis
Abstract Equivalent deductive systems were introduced in [4] with the goal of treating 1-deductive systems and algebraic 2-deductive systems in a uniform way. Results of [3], appropriately translated and strengthened, show that two deductive systems over the same language type are equivalent if and only if their lattices of theories are isomorphic via an isomorphism that commutes with substitutions. Deductive equivalence of , -institutions [14, 15] generalizes the notion of equivalence of deductive systems. In [15, Theorem 10.26] this criterion for the equivalence of deductive systems was generalized to a criterion for the deductive equivalence of term , -institutions, forming a subclass of all , -institutions that contains those , -institutions directly corresponding to deductive systems. This criterion is generalized here to cover the case of arbitrary , -institutions. [source]

Accelerated Reliability Qualification in Automotive Testing

QUALITY AND RELIABILITY ENGINEERING INTERNATIONAL, Issue 2 2004
Alex Porter
Abstract Products must come to market quickly, be more reliable and cost less. The problem is that statistical measures take time. There is a clear need for actionable information about the robustness or durability of a product early in the development process. In a Failure Mode Verification Test (FMVT), the analysis is not statistical but is designed to check two assumptions. First, that the design is capable of producing a viable product for the environments applied. Second, that a good design and fabrication of the product would last for a long period of time under all of the stresses that it is expected to see and would accumulate stress damage throughout the product in a uniform way. Testing a product in this way leads to three measures of the product's durability: (1) design maturity, the ratio between time to first failure and the average time between failures after the first failure; (2) technological limit, the time under test at which fixing additional failures would not provide a significant improvement in the life of the product; and (3) failure mode histogram, which indicates the repeatability of failures in a product. Using techniques like FMVT can provide a means of breaking the tyranny of statistics over durability and reliability testing in a competitive business climate. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Prospective Evaluation of Intraoperative Hemodynamics in Liver Transplantation with Whole, Partial and DCD Grafts

AMERICAN JOURNAL OF TRANSPLANTATION, Issue 8 2010
M. Sainz-Barriga
The interaction of systemic hemodynamics with hepatic flows at the time of liver transplantation (LT) has not been studied in a prospective uniform way for different types of grafts. We prospectively evaluated intraoperative hemodynamics of 103 whole and partial LT. Liver graft hemodynamics were measured using the ultrasound transit time method to obtain portal (PVF) and arterial (HAF) hepatic flow. Measurements were recorded on the native liver, the portocaval shunt, following reperfusion and after biliary anastomosis. After LT HAF and PVF do not immediately return to normal values. Increased PVF was observed after graft implantation. Living donor LT showed the highest compliance to portal hyperperfusion. The amount of liver perfusion seemed to be related to the quality of the graft. A positive correlation for HAF, PVF and total hepatic blood flow with cardiac output was found (p = 0.001). Portal hypertension, macrosteatosis >30%, warm ischemia time and cardiac output, independently influence the hepatic flows. These results highlight the role of systemic hemodynamic management in LT to optimize hepatic perfusion, particularly in LDLT and split LT, where the highest flows were registered. [source]