Numerical Simulations of Transcritical Natural Convection

In modern engineering applications, system overheating is a key issue that needs to be solved with efficient and reliable cooling technologies. Among the possible mechanisms that these are based on, natural convection cooling is one of the most frequently employed, with applications ranging from cooling of computer micro-components to large nuclear reactors. While many studies have been performed on natural convection employing supercritical or subcritical fluids, little attention has been given to fluids in their transcritical regime. The latter has the potential to yield high performances while avoiding detrimental effects of two-phase systems (e.g. cavitation). In the present study, 2D simulations of a theoretical transcritical natural convection cooling system are performed. Thermal properties changes and their influences on the overall heat transfer dynamics are investigated. To assess the performance of transcritical natural convection, heat flux and frequency content of hydrodynamic mixing are analyzed. Two fluids are employed (H20 and R134a), with four different temperature settings. Flow visualizations show circulations patterns typical of natural convection but with peculiarities due to pseudo-boiling conditions such as absence of nucleate boiling. With increasing top-down temperature difference, steady-state equilibrium heat flux is achieved sooner. Dimensional scaling techniques are used to collapse heat flux time spectra for all the temperature differences considered. This study is the first step towards high-fidelity numerical modeling and understanding of transcritical fluid behavior in natural convection systems that can be used in high-performance cooling devices

Locally-Adaptive Tabulation of Low-Dimensional Manifolds using Bezier Patch Reconstruction

An efficient tabulation strategy for turbulent combustion simulations is proposed. Using a locally adaptive arrangement of structured Bezier patches–often used in computer graphics–the combustion manifold can be efficiently tabulated; thus reducing the table size by over an order of magnitude while maintaining high accuracy. A hybrid search algorithm is implemented that uses a one-step quadrant analysis followed by a linear search to minimize the cost of the data retrieval. The present tabulation has been successfully applied to flamelet/progress variable approach (FPVA) and trajectory generated low-dimensional manifold (TGLDM). The error, computational size and search-and-retrieval time are quantified and compared against classical tabulation approaches.NSERC USRA NSERC RGPI

A single fast radio burst localized to a massive galaxy at cosmological distance

Fast radio bursts (FRBs) are brief radio emissions from distant astronomical sources. Some are known to repeat, but most are single bursts. Nonrepeating FRB observations have had insufficient positional accuracy to localize them to an individual host galaxy. We report the interferometric localization of the single-pulse FRB 180924 to a position 4 kiloparsecs from the center of a luminous galaxy at redshift 0.3214. The burst has not been observed to repeat. The properties of the burst and its host are markedly different from those of the only other accurately localized FRB source. The integrated electron column density along the line of sight closely matches models of the intergalactic medium, indicating that some FRBs are clean probes of the baryonic component of the cosmic web

Mitochondrial physiology

As the knowledge base and importance of mitochondrial physiology to evolution, health and disease expands, the necessity for harmonizing the terminology concerning mitochondrial respiratory states and rates has become increasingly apparent. The chemiosmotic theory establishes the mechanism of energy transformation and coupling in oxidative phosphorylation. The unifying concept of the protonmotive force provides the framework for developing a consistent theoretical foundation of mitochondrial physiology and bioenergetics. We follow the latest SI guidelines and those of the International Union of Pure and Applied Chemistry (IUPAC) on terminology in physical chemistry, extended by considerations of open systems and thermodynamics of irreversible processes. The concept-driven constructive terminology incorporates the meaning of each quantity and aligns concepts and symbols with the nomenclature of classical bioenergetics. We endeavour to provide a balanced view of mitochondrial respiratory control and a critical discussion on reporting data of mitochondrial respiration in terms of metabolic flows and fluxes. Uniform standards for evaluation of respiratory states and rates will ultimately contribute to reproducibility between laboratories and thus support the development of data repositories of mitochondrial respiratory function in species, tissues, and cells. Clarity of concept and consistency of nomenclature facilitate effective transdisciplinary communication, education, and ultimately further discovery