The wake of hovering flight in bats

Hovering means stationary flight at zero net forward speed, which can be achieved by animals through muscle powered flapping flight. Small bats capable of hovering typically do so with a downstroke in an inclined stroke plane, and with an aerodynamically active outer wing during the upstroke. The magnitude and time history of aerodynamic forces should be reflected by vorticity shed into the wake. We thus expect hovering bats to generate a characteristic wake, but this has until now never been studied. Here we trained nectar-feeding bats, Leptonycteris yerbabuenae, to hover at a feeder and using time-resolved stereoscopic particle image velocimetry in conjunction with high-speed kinematic analysis we show that hovering nectar-feeding bats produce a series of bilateral stacked vortex loops. Vortex visualizations suggest that the downstroke produces the majority of the weight support, but that the upstroke contributes positively to the lift production. However, the relative contributions from downstroke and upstroke could not be determined on the basis of the wake, because wake elements from down- and upstroke mix and interact. We also use a modified actuator disc model to estimate lift force, power and flap efficiency. Based on our quantitative wake-induced velocities, the model accounts for weight support well (108%). Estimates of aerodynamic efficiency suggest hovering flight is less efficient than forward flapping flight, while the overall energy conversion efficiency (mechanical power output/metabolic power) was estimated at 13%.     

NMR法研究羧甲基羟丙基纤维素的取代结构

羧甲基羟两基纤维素(CMHPC)经水解和乙酰化反应后,利用~1H NMR和~(13)C NMR谱确定其取代度和取代基分布,提出了纤维素葡萄糖单元上羟基的相对反应活性顺序。     

8步掌控你的新单反

新年新气象,你有没有打算给自己购置一台全新的数码单反相机呢?在这篇文章中,Ed Godden将告诉你如何才能发挥出你的新相机的全部潜能。很多读者告诉我们说,他们新买的数码单反相机的功能太过复杂,简直让他们无从下手,他们想要知道怎样才能拍摄出最好的照片,以及如何正确的设置相机参数。     

Causal client models in selecting effective interventions: A cognitive mapping study.

An important reason to choose an intervention to treat psychological problems of clients is the expectation that the intervention will be effective in alleviating the problems. The authors investigated whether clinicians base their ratings of the effectiveness of interventions on models that they construct representing the factors causing and maintaining a client's problems. Forty clinical child psychologists drew causal models and rank ordered interventions according to their expected effectiveness for 2 cases. The authors found that different clinicians constructed different causal models for the same client. Also, the authors found low to moderate agreement about the effectiveness of different interventions. Nevertheless, the authors could predict clinicians' ratings of effectiveness from their individual causal models. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Synthesis and characterization of (BaxSr1−x)Ti1+yO3+z thin films and integration into microwave varactors and phase shifters

Abstract

Precise control of composition and microstructure is critical for the production of (Ba_xSr_1?x)Ti_1+yO_3+z (BST) dielectric thin films with the large dependence of permittivity on electric field, low losses, and high electrical breakdown fields that are required for successful integration of BST into tunable high frequency devices. Here we review recent results on composition-microstructure-electrical property relationships of polycrystalline BST films produced by magnetron sputter deposition, that are appropriate for microwave devices such as phase shifters. Films with controlled compositions were grown from a stoichiometric Ba_0.5Sr_0.5TiO₃ target by control of the background processing gas pressure. It was determined that the (Ba+Sr)/Ti ratios of these BST films could be adjusted from 0.73 to 0.98 by changing the total (Ar+O₂) process pressure, while the O₂/Ar ratio did not strongly affect the metal ion composition. Film crystalline structure and dielectric properties as a function of the (Ba+Sr)/Ti ratio are discussed. Optimized BST layers yielded capacitors with low dielectric losses (0.0047), among the best reported for sputtered BST, while still maintaining tunabili-ties suitable for device applications. These BST films were used to produce distributed-cir-cuit phase-shifters, using a discrete periodic loading of a coplanar waveguide with integrated BST varactors on high-resistivity silicon. Phase shifters yielding 30 degrees of phase shift per dB of insertion loss were demonstrated at 20GHz.     

Methane Oxyforming for Synthesis Gas Production

This article is concerned with the reforming of methane to synthesis gas; a review of the steam reforming Rxn is presented, and the dry reforming and partial oxidation Rxns introduced. Collectively, these processes are known as “oxyforming.” A background to oxyforming, industrial practice, and some of the most important latest developments will be presented, along with a section on the uses of synthesis gas. The current understanding of the Rxn mechanisms for the three processes and the problem of deactivation by carbon deposition will be discussed in detail. Finally, the economics of synfuel production will be addressed and compared with the production of other fuels, and the future directions and outlook for oxyforming will be forwarded. This article should allow the reader to make comparisons between these three important industrial reactions.     

Dead zones in porous catalysts: Concentration profiles and efficiency factors

This paper examines the conditions under which a dead zone, or a portion of the catalyst devoid of reactant, can form in a porous catalyst in which simultaneous reaction and diffusion are occurring. The condition that allows for the existence of a dead zone is defined by a critical Thiele modulus. When the Thiele modulus – the ratio of chemical reaction to diffusion – is greater than the critical Thiele modulus, a dead zone exists. This dead zone can be mathematically defined by a change of boundary conditions. We examine nth order reactions in isothermal infinite slabs, infinite cylinders, and spheres. In addition, we provide analytical concentration profiles and efficiency factors for zero-order reactions in non-isothermal infinite slabs (in the so-called low beta approximation). We also discuss some common errors and misconceptions associated with this phenomenon.