Analogous Problem (analogous + problem)

Distribution by Scientific Domains

Selected Abstracts

Constructal tree-shaped paths for conduction and convection

Adrian Bejan
Abstract This lecture reviews a series of recent results based on the geometric minimization of the resistance to flow between one point (source, sink) and a volume or an area (an infinity of points). Optimization is achieved by varying the geometric features of the flow path subject to volume constraints. The method is outlined by using the problem of steady volume-point conduction. Optimized first is the smallest elemental volume, which is characterized by volumetric heat generation in a low-conductivity medium, and one-dimensional conduction through a high-conductivity ,channel'. Progressively larger volumes are covered by assemblies of previously optimized constructs. Tree-shaped flow structures spring out of this objective and constraints principle. Analogous problems of fluid flow, and combined heat and fluid flow (convection, trees of fins) are also discussed. The occurrence of similar tree structures in nature may be reasoned based on the same principle (constructal theory) (Bejan, 2000). Copyright 2003 John Wiley & Sons, Ltd. [source]

Numerical simulation of non-isothermal phase change problem using ADRBEM with augmented items

Jie Liu
Abstract In this paper, the phase change moving interface problem along the axial direction of the cylinder in the lead alloys containing tin is simulated by the axisymmetric dual reciprocity boundary element method (ADRBEM) with augmented items. The numerical method is verified by comparing with the analytical solution under a certain condition. The calculating results show that the ADRBEM with augmented items is an effective numerical method to solve the analogous problem of non-isothermal phase change, which occurs in the crystal growth process. 2007 Wiley Periodicals, Inc. Heat Trans Asian Res, 36(7): 408, 416, 2007; Published online in Wiley InterScience ( DOI 10.1002/htj.20173 [source]

An integral formulation procedure for the solutions to Helmholtz's equation in spherically symmetric media

Giacomo Caviglia
Abstract Starting from Helmholtz's equation in inhomogeneous media, the associated radial second-order equation is investigated through a Volterra integral equation. First the integral equation is considered in a sphere. Boundedness, uniqueness and existence of the (regular) solution are established and the series form of the solution is provided. An estimate is determined for the error arising when the series is truncated. Next the analogous problem is considered for a spherical layer. Again, boundedness, uniqueness and existence of two base solutions are established and error estimates are determined. The procedure proves more effective in the sphere. Copyright 2009 John Wiley & Sons, Ltd. [source]

Tropical-cyclone intensification and predictability in three dimensions

Nguyen Van Sang
Abstract We present numerical-model experiments to investigate the dynamics of tropical-cyclone amplification and its predictability in three dimensions. For the prototype amplification problem beginning with a weak-tropical-storm-strength vortex, the emergent flow becomes highly asymmetric and dominated by deep convective vortex structures, even though the problem as posed is essentially axisymmetric. The asymmetries that develop are highly sensitive to the boundary-layer moisture distribution. When a small random moisture perturbation is added in the boundary layer at the initial time, the pattern of evolution of the flow asymmetries is changed dramatically, and a non-negligible spread in the local and azimuthally-averaged intensity results. We conclude, first, that the flow on the convective scales exhibits a degree of randomness, and only those asymmetric features that survive in an ensemble average of many realizations can be regarded as robust; and secondly, that there is an intrinsic uncertainty in the prediction of maximum intensity using either maximum-wind or minimum-surface-pressure metrics. There are clear implications for the possibility of deterministic forecasts of the mesoscale structure of tropical cyclones, which may have a major impact on the intensity and on rapid intensity changes. Some other aspects of vortex structure are addressed also, including vortex-size parameters, and sensitivity to the inclusion of different physical processes or higher spatial resolution. We investigate also the analogous problem on a ,-plane, a prototype problem for tropical-cyclone motion. A new perspective on the putative role of the wind--evaporation feedback process for tropical-cyclone intensification is offered also. The results provide new insight into the fluid dynamics of the intensification process in three dimensions, and at the same time suggest limitations of deterministic prediction for the mesoscale structure. Larger-scale characteristics, such as the radius of gale-force winds and ,-gyres, are found to be less variable than their mesoscale counterparts. Copyright 2008 Royal Meteorological Society [source]

Porcine induced pluripotent stem cells may bridge the gap between mouse and human iPS

IUBMB LIFE, Issue 4 2010
Miguel A. Esteban
Abstract Recently, three independent laboratories reported the generation of induced pluripotent stem cells (iPSCs) from pig (Sus scrofa). This finding sums to the growing list of species (mouse, human, monkey, and rat, in this order) for which successful reprogramming using exogenous factors has been achieved, and multiple others are possibly forthcoming. But apart from demonstrating the universality of the network identified by Shinya Yamanaka, what makes the porcine model so special? On one side, pigs are an agricultural commodity and have an easy and affordable maintenance compared with nonhuman primates that normally need to be imported. On the other side, resemblance (for example, size of organs) of porcine and human physiology is striking and because pigs are a regular source of food the ethical concerns that still remain in monkeys are not applicable. Besides, the prolonged lifespan of pigs compared with other domestic species can allow exhaustive follow up of side effects after transplantation. Porcine iPSCs may thus fill the gap between the mouse model, which due to its ease is preferred for mechanistic studies, and the first clinical trials using iPSCs in humans. However, although these studies are relevant and have created significant interest they face analogous problems that we discuss herein together with potential new directions. 2010 IUBMB IUBMB Life, 62(4): 277,282, 2010 [source]