EFFECT OF FIN THICKNESS ON FLOW AND HEAT TRANSFER IN MULTI-LOUVERED FINS

ABSTRACT High-resolution time-dependent numerical simulations are used to investigate the effect of thickness ratio on fluid flow and heat transfer performance in multi-louvered fins. Results for three fin thickness ratios, two louver angles, and a fin pitch to louver pitch ratio of one are reported for Reynolds number ranging from 50 to 1200. Thickness ratio is found to have a significant effect on flow efficiency, especially in geometries with small louver angles. For small louver angles, increasing thickness to louver pitch ratio from 0.05 to 0.15, decreases the flow efficiency by as much as 35-40%. As expected, increasing thickness ratio increases total pressure drop, most of which results from an increase in form drag. Heat transfer coefficient, on the other hand, is not influenced strongly by the thickness ratio. The increase in flow acceleration and local Reynolds number with increase in thickness ratio, on one hand, is offset by low flow efficiencies and recirculation zones on the other. As a consequence, some heat transfer degradation is found at low Reynolds numbers, however the degradation diminishes as the Reynolds number increases beyond 300. In general, larger thickness ratios lead to a lower ratio of j/f

Momentum-independent magnetic excitation continuum in the honeycomb iridate H3_3LiIr2_2O6_6

In the search for realizations of Quantum Spin Liquids (QSL), it is essential to understand the interplay between inherent disorder and the correlated fluctuating spin ground state. H$_3$LiIr$_2$O$_6$ is regarded as a spin liquid proximate to the Kitaev-limit (KQSL) in which H zero-point motion and stacking faults are known to be present. Bond disorder has been invoked to account for the existence of unexpected low-energy spin excitations. Controversy remains about the nature of the underlying correlated state and if any KQSL physics survives. Here, we use resonant X-ray spectroscopies to map the collective excitations in H$_3$LiIr$_2$O$_6$ and characterize its magnetic state. We uncover a broad bandwidth and momentum-independent continuum of magnetic excitations at low temperatures that are distinct from the paramagnetic state. The center energy and high-energy tail of the continuum are consistent with expectations for dominant ferromagnetic Kitaev interactions between dynamically fluctuating spins. The absence of a momentum dependence to these excitations indicates a broken translational invariance. Our data support an interpretation of H$_3$LiIr$_2$O$_6$ as a disordered topological spin liquid in close proximity to bond-disordered versions of the KQSL. Our results shed light on how random disorder affects topological magnetic states and have implications for future experimental and theoretical works toward realizing the Kitaev model in condensed matter system

High order algorithms for the management of uncertainties with applications in space situational awareness

Space situational awareness program, for both NEO and debris segments, have to face the challenging problem of accurately managing uncertainties in highly nonlinear dynamical environments. The uncertainties affect all the main phases necessary for the successful realization of the program; i.e., orbital determination, ephemeris prediction, collision probability computation, and collision avoidancemaneuver planning and execution. Since the amount of data that must be processed is huge, efficient methods for the management of uncertainties are required. Differential algebraic (DA) techniques can represent a valuable tool to address this tasks. Differential algebra supplies the tools to compute the derivatives of functions within a computer environment. This technique allows for the efficient computation of high-order expansions of the flow of ordinary differential equations (with respect to initial conditions and/or model parameters) and the approximation of the solution manifold of implicit equations in Taylor series. These two features constitute the building blocks of a set new algorithms for the nonlinear and efficient management of uncertainties. Applications to 1) angles-only preliminary orbit determination 2) propagation of orbital dynamics 3) nonlinear filtering 4) space conjunction prediction 5) robust optimal control are presented to prove the efficiency of DA based algorithms

The Current State of Performance Appraisal Research and Practice: Concerns, Directions, and Implications

On the surface, it is not readily apparent how some performance appraisal research issues inform performance appraisal practice. Because performance appraisal is an applied topic, it is useful to periodically consider the current state of performance research and its relation to performance appraisal practice. This review examines the performance appraisal literature published in both academic and practitioner outlets between 1985 and 1990, briefly discusses the current state of performance appraisal practice, highlights the juxtaposition of research and practice, and suggests directions for further research

Uncovering the Genetic Landscape for Multiple Sleep-Wake Traits

Despite decades of research in defining sleep-wake properties in mammals, little is known about the nature or identity of genes that regulate sleep, a fundamental behaviour that in humans occupies about one-third of the entire lifespan. While genome-wide association studies in humans and quantitative trait loci (QTL) analyses in mice have identified candidate genes for an increasing number of complex traits and genetic diseases, the resources and time-consuming process necessary for obtaining detailed quantitative data have made sleep seemingly intractable to similar large-scale genomic approaches. Here we describe analysis of 20 sleep-wake traits from 269 mice from a genetically segregating population that reveals 52 significant QTL representing a minimum of 20 genomic loci. While many (28) QTL affected a particular sleep-wake trait (e.g., amount of wake) across the full 24-hr day, other loci only affected a trait in the light or dark period while some loci had opposite effects on the trait during the light vs. dark. Analysis of a dataset for multiple sleep-wake traits led to previously undetected interactions (including the differential genetic control of number and duration of REM bouts), as well as possible shared genetic regulatory mechanisms for seemingly different unrelated sleep-wake traits (e.g., number of arousals and REM latency). Construction of a Bayesian network for sleep-wake traits and loci led to the identification of sub-networks of linkage not detectable in smaller data sets or limited single-trait analyses. For example, the network analyses revealed a novel chain of causal relationships between the chromosome 17@29cM QTL, total amount of wake, and duration of wake bouts in both light and dark periods that implies a mechanism whereby overall sleep need, mediated by this locus, in turn determines the length of each wake bout. Taken together, the present results reveal a complex genetic landscape underlying multiple sleep-wake traits and emphasize the need for a systems biology approach for elucidating the full extent of the genetic regulatory mechanisms of this complex and universal behavior