901 publications from this institution
What is evolution and why does it exist in the biological, geophysical and technological realms - in short, everywhere? Why is there a time direction - a time arrow - in the changes we know are happening every moment and everywhere? Why is the present different than the past? These are questions of physics, about everything, not just biology. The answer is that nothing lives, flows and moves unless it is driven by power. Physics sheds light on the natural engines that produce the power destroyed by the flows, and on the free morphing that leads to flow architectures naturally and universally. There is a unifying tendency across all domains to evolve into flow configurations that provide greater access for movement. This tendency is expressed as the constructal law of evolutionary flow organization everywhere. Here I illustrate how this law of physics accounts for and unites the life and evolution phenomena throughout nature, animate and inanimate.
No abstract is provided for this article.
The architecture of heat exchangers is a classical subject that has been studied extensively in the past. In this paper, we address the fundamental question of what the size of the heat exchanger should be, in addition to what architectural features it should have. The answer to the size question follows from the tradeoff between (1) the useful power lost because of heat transfer and fluid flow and (2) the power destroyed during transportation, manufacturing, and maintenance. Changes in heat exchanger size induce changes in the opposite sign in the power requirements (1) and (2). This fundamental tradeoff regarding size is illustrated by considering one side of a heat exchanger (one flow passage) in laminar flow and in fully rough turbulent flow, with several duct cross sectional shapes and arrays of channels in parallel. The size tradeoff is present in heat exchanger applications across the board, from vehicles to stationary power plants.
ABSTRACT Preterm birth is a syndrome that is triggered by diverse biological pathways and presents with many comorbid diseases. Although twin studies reveal a substantial heritable component, the genetic mechanisms of preterm birth remain poorly understood. We hypothesize that refining the preterm birth phenotype will reveal sub-phenotypes associated with distinct genetic risk factors and potential treatments. Here, we leverage rich longitudinal data from electronic health records (EHRs) from over 60,000 individuals from two clinical sites. Using tensor decomposition, we uncover several latent factors (LFs) that capture coherent combinations of comorbidities (e.g., metabolic, inflammatory, and mental health) and temporal trajectories of preterm and term births. Similar LFs are discovered between the two sites, underscoring their interpretability. Machine learning models trained on LFs accurately predict preterm birth and perform comparably to models trained on the full EHR data. Integrating genome-wide genotyping for >2,200 individuals, we find robust associations of preterm birth risk with high polygenic burden for cardiovascular disease, type 2 diabetes and body mass index. Using LFs, we discover that these genetic signals are strongly and specifically associated with different subsets of the preterm birth cohort. For example, the polygenic diabetes risk is associated with a LF characterized by relevant metabolic disorders. In summary, our study integrates latent phenotypes discovered from large EHR datasets with genetic data to predict preterm birth risk, uncover disease subtypes and comorbidities that drive genetic associations, and delineate the mechanisms underlying the heterogeneity of this complex trait.
No abstract is provided for this article.
The objective of the Journal of Mechanics is to provide an international forum to foster exchange of ideas among mechanics communities in different parts of world.
ComplexityComplexity is a lot like freedomFreedom: everybody knows, but very few can tell what it is. Complex is often confused with complicated and random. ComplexityComplexity, organizationOrganization, and evolutionEvolution in natureNature are most powerful and...
Numerical calculation from the full differential equations for convection in an unbounded region is expensive, and hence approximate solutions are important. For small values of the Rayleigh number Ra, perturbation methods are appropriate. At large values of Ra...
We start with the simplest case, that of zero flow through the fluid-saturated porous medium. For an equilibrium state the momentum equation is satisfied if (6.1) % MathType!MTEF!2!1!+- %...
Here we document the effect of flow configuration on the heat transfer performance of a spiral shaped pipe embedded in a cylindrical conducting volume. We considered several configurations with fixed volumes of fluid and solid. First, we optimized the geometry of two spiral pipes with varying spacing between the spiral turns and the vertical spacing between the two spirals. Next, we extended the method to three spiral pipes with varying the spacing between the spiral turns and the spacing between the spiral pipes, and changing the dimensions of the conducting volume. We found that optimal spacings between the spiral turns and spire planes exist, such that the volumetric heat transfer rate is maximal. The optimized features of the heat transfer architecture are robust.
Four problems are used to show how the following objectives can be pursued in a heat transfer course: the introduction of design principles along with heat transfer science, the interdisciplinary character of heat transfer engineering, and the relationship between heat transfer and other engineering disciplines. The problems address the design question of how to select the shape and material of a mechanical support that must be a good thermal insulator at the same time. They show that the mechanical and thermal functions of the system compete against one another, and that it is possible to balance these competing objectives into an optimal design.
This paper reports a complete theory of the melting that occurs in a confined porous medium saturated with phase-change material and heated from the side. Darcy flow characteristics are assumed for the liquid phase. The solid phase is isothermal and at the melting point. The first part of the paper reports a matched boundary layer solution for natural convection dominated melting in the quasi-steady regime. The second part reports a solution for the heat transfer during the two earlier regimes, pure conduction followed by mixed conduction and convection. Together, the two solutions cover the entire history of transient heating administered from the side. This theory shows that the liquid-side Stefan number has a profound effect on the heat transfer and melting rates.
This paper details the generation of multi-scale flow structure in a package with heat sources. The model is based on abandoning two common assumptions (1) the assumption that there are many channels (components) in the package, which is traditionally made to exploit simplifications due to symmetry, and (2) the assumption that the heat-generating components have negligible thickness. Numerical simulations document the flow stagnation and separation generated by blunt heat sources, and the effect of these flow phenomena on the optimized internal flow structure. The effect of asymmetric thermal boundary conditions on the optimal spacing between heat-generating plates is significant. If the package has some channels with symmetric boundary conditions, and some with asymmetric boundary conditions, then the optimal structure has multiple spacings. The effect of freedom on design performance is documented by optimizing competing configurations that have different numbers of degrees of freedom.
This paper shows that the internal structure (relative sizes, spacings) of a fuel cell can be optimized so that performance is maximized at the global level. The optimization of flow geometry begins at the smallest (elemental) level, where the fuel cell is modelled as a unidirectional flow system. The polarization curve, power and efficiency are obtained as functions of temperature, pressure, geometry and operating parameters. Although the model is illustrated for an alkaline fuel cell, it may be applied to other fuel cell types by changing the reaction equations and accounting for the appropriate energy interactions. The optimization of the internal structure is subjected to fixed total volume. There are four degrees of freedom in the optimization, which account for the relative thicknesses of the two (anode and cathode) diffusion layers, two reaction layers and the space occupied by the electrolyte solution. The available volume is distributed optimally through the system so that the total power is maximized. Numerical results show that the optima are sharp, and must be identified accurately. Temperature and pressure gradients play important roles, especially as the fuel and oxidant flow paths increase. The optimized internal structure is reported in dimensionless form. Directions for future improvements in flow architecture (constructal design) are discussed. Copyright © 2004 John Wiley & Sons, Ltd.
Design happens everywhere, whether in animate objects (e.g., dendritic lung structures, bacterial colonies, and corals), inanimate patterns (river basins, beach slope, and dendritic crystals), social dynamics (pedestrian traffic flows), or engineered systems (heat dissipation in electronic circuitry). This “design in nature” often takes on remarkably similar patterns, which can be explained under one unifying Constructal Law. This book explores the unifying power of the Constructal Law and its applications in all domains of design generation and evolution, ranging from biology and geophysics to globalization, energy, sustainability, and security. The Constructal Law accounts for the universal tendency of flow systems to morph into evolving configurations that provide greater and easier access over time. The Constructal Law resolves the many and contradictory ad hoc statements of “optimality”, end design, and destiny in nature, such as minimum and maximum entropy production and minimum and maximum flow resistance, and also explains the designs that are observed and copied in biomimetics. Constructal Law and the Unifying Principle of Design covers the fundamentals of Constructal Theory and Design, as well as presenting a variety of state-of-the-art applications. Experts from the biological, physical and social sciences demonstrate the unification of all design phenomena in nature, and apply this knowledge to novel designs in modern engineering, such as vascularization for self-healing and self-cooling materials for aircraft, and tree fins and cavities for heat transfer enhancement.
We start with the simplest case, that of zero flow through the fluid-saturated porous medium. For an equilibrium state, the momentum equation is satisfied if $$ - \nabla P + {{\rho}_{\mathrm{ f}}}g = 0. $$...
The objective of the Journal of Mechanics is to provide an international forum to foster exchange of ideas among mechanics communities in different parts of world.
This paper describes a numerical and theoretical study of the transient natural convection heating of a two-dimensional rectangular enclosure filled with fluid. The heating is applied suddenly along one of the side walls, while the remaining three walls are maintained insulated. It is shown that the process has two distinct phases, an early period dominated by conduction and a late period dominated by convection. The scaling laws for the heat transfer rate and the effectiveness (energy storage fraction) are determined based on scale analysis. These theoretical results are confirmed by numerical experiments conducted in the domain Ra = 103−106, Pr = 7, A = 1, where Ra is the Rayleigh number based on height and initial temperature difference, Pr is the Prandtl number, and A is the height/length ratio of the enclosure. Correlations for heat transfer rate and effectiveness are constructed by comparing the theoretical scaling laws with the numerical results.
No abstract is provided for this article.
This paper considers the question of whether the optimum phase-change temperature for maximum exergy storage is universally equal to the geometric mean of the heat source and environment temperature, Tm=(T∞Te)1/2. The study consists of three parts. The first deals with the conduction-melting process, and shows that the optimum melting temperature is generally greater than the geometric mean of the source and environment temperatures. The second part covers the conduction-solidification process, and concludes that the irreversibility of solidification decreases monotonically as the phase-change temperature increases. The third part treats the complete cycle of melting (storage) followed by solidification (retrieval), and demonstrates that the optimum phase-change temperature is greater than the optimum temperature of the melting process alone.
