Exploiting the Synergy Between Gossiping and Structured Overlays

In this position paper we argue for exploiting the synergy between gossip-based algorithms and structured overlay networks (SON). These two strands of research have both aimed at building fault-tolerant, dynamic, self-managing, and large-scale distributed systems. Despite the common goals, the two areas have, however, been relatively isolated. We focus on three problem domains where there is an untapped potential of using gossiping combined with SONs. We argue for applying gossip-based membership for ring-based SONs---such as Chord and Bamboo---to make them handle partition mergers and loopy networks. We argue that small world SONs---such as Accordion and Mercury---are specifically well-suited for gossip-based membership management. The benefits would be better graph-theoretic properties. Finally, we argue that gossip-based algorithms could use the overlay constructed by SONs. For example, many unreliable broadcast algorithms for SONs could be augmented with anti-entropy protocols. Similarly, gossip-based aggregation could be used in SONs for network size estimation and load-balancing purposes

Review of Experimental Work in Biomimetic Foils

Significant progress has been made in understanding some of the basic mechanisms of force production and flow manipulation in oscillating foils for underwater use. Biomimetic observations, however, show that there is a lot more to be learned, since many of the functions and details of fish fins remain unexplored. This review focuses primarily on experimental studies on some of the, at least partially understood, mechanisms, which include 1) the formation of streets of vortices around and behind two- and three-dimensional propulsive oscillating foils; 2) the formation of vortical structures around and behind two- and three-dimensional foils used for maneuvering, hovering, or fast-starting; 3) the formation of leading-edge vortices in flapping foils, under steady flapping or transient conditions; 4) the interaction of foils with oncoming, externally generated vorticity; multiple foils, or foils operating near a body or wall

Space deployable domed solar concentrator with foldable panels and hinge therefor

A space deployable solar energy concentrator is formed of a dome-shaped arrangement of compactly stowable flat panel segments mounted on a collapsible, space-deployable support structure of interconnected linear components. The support structure is comprised of a plurality of tensioned, curvilinear edge strips which extend in a radial direction from a prescribed vertex of a surrounding umbrella-like framework of radially extending rib members. Between a respective pair of radially-extending, curvilinear edge strips an individual wedge-shaped panel section is formed of a plurality of multi-segment lens panel strips each of which is supported in tension between the pair of edge strips by a pair of circumferentially extending catenary cord members connected to a pair of ribs of the surrounding umbrella-like framework. A respective lens panel strip is comprised of a plurality of flat, generally rectangular-shaped, energy-directing panels arranged side-by-side in the circumferential direction of the dome. Adjacent panels are interconnected by flexible U-shaped hinges which overlap opposing edges of adjacent panels and engage respective cylindrically-shaped, load distribution bars that slide within the flexible hinges. Because each U-shaped hinge is flexible, it is permitted to shift in the circumferential direction of the panel section to facilitate stowage and deployment of the dome

Unsteady forces on an accelerating plate and application to hovering insect flight

The aerodynamic forces on a flat plate accelerating from rest at fixed incidence in two-dimensional power-law flow are studied analytically and numerically. An inviscid approximation is made in which separation at the two plate edges is modelled by growing spiral vortex sheets, whose evolution is determined by the Birkhoff–Rott equation. A solution based on a similarity expansion is developed, valid when the scale of the separated vortex is much smaller than the plate dimension. The leading order is given by the well-known similarity growth of a vortex sheet from a semi-infinite flat plate, while equations at the second order describe the asymmetric sweeping effect of that component of the free-stream parallel to the plate. Owing to subtle cancellation, the unsteady vortex force exerted on the plate during the starting motion is independent of the sweeping effect and is determined by the similarity solution, to the order calculated. This gives a mechanism for dynamic stall based on a combination of unsteady vortex lift and pure added mass; the incidence angle for maximum vortex lift is $\arccos \sqrt{3/8}\,{\approx}\,52.2^\circ$ independent of the acceleration profile. Circulation on the flat plate makes no direct contribution. Both lift and drag force predictions from the unsteady inviscid theory are compared with those obtained from numerical solutions of the two-dimensional unsteady Navier–Stokes equations for an ellipse of high aspect ratio, and with predictions of Wagner's classical theory. There is good agreement with numerical results at high incidence and moderate Reynolds number. The force per unit span predicted by the vortex theory is evaluated for parameters typical of insect wings and is found to be in reasonable agreement with numerical simulations. Estimates for the shed circulation and the size of the start-up vortices are also obtained. The significance of this flow as a mechanism for insect hovering flight is discussed

Momentum 2011

A journal of undergraduate researchhttps://csuepress.columbusstate.edu/momentum/1002/thumbnail.jp

Lightweight solar panel development

Preliminary design, fabrication, and test of lightweight solar panel of built-up beryllium structure with 29 sq ft active cell are

Resource reservation protocols for optical burst switched networks

Nesta disserta c~ao e feito um estudo em redes com comuta c~ao optica de agregados de pacotes (redes OBS). Assim, este estudo apresenta e descreve os conceitos mais importantes relacionados com as redes OBS. Inicialmente e analisado o estado da arte, efectuando uma descri c~ao detalhada da arquitectura de uma rede OBS. Seguidamente analisam-se os protocolos de reserva unidireccional de recursos (JIT, JIT+, JET, Jumpstart, Horizon and E-JIT). Para isso s~ao utilizadas redes com topologias regulares (em anel e em malha) com um n umero vari avel de n os, e tamb em irregulares (NSFNET e ARPANET). E tamb em apresentado um novo protocolo de reserva unidireccional de recursos chamado E-JIT+. Este novo protocolo baseia-se no protocolo j a existente JIT+ e tenta optimizar o seu desempenho. Para melhor descrever o modo de opera c~ao deste protocolo proposto e apresentada a especi ca c~ao formal do mesmo. Depois da apresenta c~ao deste protocolo analisa-se o seu desempenho. Para isso s~ao utilizadas as topologias de rede referidas anteriormente e tamb em um simulador de redes OBS adaptado de forma a suportar o novo protocolo. O simulador utilizado, de nome OBSSimulator, devolve os valores de probabilidade de perda dos agregados de pacotes em cada salto (hop) na rede. Deste modo, foram considerados v arios factores que podem in uenciar o desempenho dos protocolos de reserva unidireccional de recursos, tais como o n umero de n os da topologia de rede utilizada, a quantidade de tr afego na rede, o ganho do grau nodal, o tempo de processamento das mensagens de setup e o tempo de con gura c~ao dos comutadores opticos. No m deste trabalho concluiu-se que o protocolo proposto, E-JIT+, melhora o desempenho em rela c~ao aos outros protocolos de reserva unidireccional de recursos estudados, nos casos estudados

Correction: New Approaches for Assessing Squid Fin Motions: Coupling Proper Orthogonal Decomposition With Volumetric Particle Tracking Velocimetry (doi:10.1242/jeb.176750)

Squid, which swim using a coupled fin/jet system powered by muscular hydrostats, pose unique challenges for the study of locomotion. The high flexibility of the fins and complex flow fields generated by distinct propulsion systems require innovative techniques for locomotive assessment. For this study, we used proper orthogonal decomposition (POD) to decouple components of the fin motions and defocusing digital particle tracking velocimetry (DDPTV) to quantify the resultant 3D flow fields. Kinematic footage and DDPTV data were collected from brief squid, Lolliguncula brevis [3.1–6.5 cm dorsal mantle length (DML)], swimming freely in a water tunnel at speeds of 0.39–7.20 DML s−1. Both flap and wave components were present in all fin motions, but the relative importance of the wave components was higher for arms-first swimming than for tail-first swimming and for slower versus higher speed swimming. When prominent wave components were present, more complex interconnected vortex ring wakes were observed, while fin movements dominated by flapping resulted in more spatially separated vortex ring patterns. Although the jet often produced the majority of the thrust for steady rectilinear swimming, our results demonstrated that the fins can contribute more thrust than the jet at times, consistently produce comparable levels of lift to the jet during arms-first swimming, and can boost overall propulsive efficiency. By producing significant drag signatures, the fins can also aid in stabilization and maneuvering. Clearly, fins play multiple roles in squid locomotion, and when coupled with the jet, allow squid to perform a range of swimming behaviors integral to their ecological success

Wake Topology and Aerodynamic Performance of Heaving Wings

Simulating the three-dimensional flow features generated by heaving wings constitutes a great challenge due to the computational effort required to compute the complex three-dimensional flow produced as a function of the kinematics parameters, wing geometry, and Reynolds number. Hereafter, we study the wake topology generated by oscillating rigid wings and the validity of the Strouhal number as the fundamental parameters used to assess the aerodynamic performance of heaving wings. The unsteady laminar incompressible Navier-Stokes equations are solved on moving overlapping structured grids using a second-order accurate in space and time finite-difference numerical method. The numerical simulations are performed at a Reynolds number of Re = 250 and at different values of Strouhal number and heaving frequency