Transition from order to chaos in the wake of an airfoil

An experimental effort is presented here that examines the nonlinear interaction of multiple frequencies in the forced wake of an airfoil. Wakes with one or two distinct frequencies behave in an ordered manner – being either locked or quasi-periodic. When a third incommensurate frequency is added to the system, the flow demonstrates chaotic behaviour. Previously, the existence of the three-frequency route to chaos has been reported only for closed system flows. It is important to note that this chaotic state is obtained at a low Reynolds number. However, the chaotic flow shows localized characteristics similar to those of high Reynolds number turbulent flows. The degree of chaotic behaviour is verified by applying ideas from nonlinear dynamics (such as Lyapunov exponents and Poincaré sections) to the experimental data, thus relating the basic physics of the system to the concepts of mode interaction and chaos. Significant changes to the vortex configuration in the wake and to the r.m.s. velocity profile occur during the transition from order to chaos

Experiments on the forced wake of an airfoil

The effect of initial flow conditions on the wake of an airfoil is examined in an experiment which uses the ‘strip heater’ technique to externally force the airfoil wake. The strip heaters are used to introduce waves into the top and bottom boundary layers of a thin symmetric airfoil which are subsequently amplified and introduced to the wake. The evolution and interaction of the waves in the wake is the primary interest of this study. A linear stability analysis is applied to the mean velocity profiles in order to understand the frequency selection process in the wake. It is seen that the mean velocity profile adjusts itself in order to become more receptive to the forced frequency of oscillation, resulting in the suppression of previously existing frequencies. The amplitude of oscillations in the wake can be controlled by varying the phase relation between two input signals. In this respect, cancellation and enhancement of the oscillations is possible. The linear stability analysis is applied to the cancellation/enhancement flow to verify the level of cancellation achieved. The receptivity of the system to external forcing is established. A substantial reduction in drag is achieved for forcing frequencies near the centre of the receptivity range

The combline filter and phase-lock loop. A new technique to improve FM television reception

Development and performance of combline filter phase locked loop combination for television receptio

A Distributed Parameters Model for Solar Cells

Distributive circuit element model for solar cells with series and shunt path

New filter technique improves home television reception

Program studies and designs combline filters and analyzes their effectiveness in improving TV quality. Signal tracking methods are improved. Combline phase-lock loop provides significant sensitivity improvement above and below threshold

Loci Controlling Resistance to High Plains Virus and Wheat Streak Mosaic Virus in a B73 × Mo17 Population of Maize

High Plains disease has the potential to cause significant yield loss in susceptible corn (Zea mays L.) and wheat (Triticum aestivum L.) genotypes, especially in the central and western USA. The primary causal agent, High Plains virus (HPV), is vectored by wheat curl mite (WCM; Aceria tossicheila Keifer), which is also the vector of wheat streak mosaic virus (WSMV). In general, the two diseases occur together as a mixed infection in the field. The objective of this research was to characterize the inheritance of HPV and WSMV resistance using B73 (resistant to HPV and WSMV) × Mo17 (moderately susceptible to HPV and WSMV) recombinant inbred lines. A population of 129 recombinant inbred lines scored for 167 molecular markers was used to evaluate resistance to WSMV and to a mixed infection of WSMV and HPV. Loci conferring resistance to systemic movement of WSMV in plants mapped to chromosomes 3, 6, and 10, consistent with the map position of wsm2, wsm1, and wsm3, respectively. Major genes for resistance to systemic spread of HPV in doubly infected plants mapped to chromosomes 3 and 6, coincident or tightly linked with the WSMV resistance loci. Analysis of doubly infected plants revealed that chromosome 6 had a major effect on HPV resistance, consistent with our previous analysis of B73 × W64A and B73 × Wf9 populations. Quantitative trait loci (QTL) affecting resistance to localized symptom development mapped to chromosomes 4 (umc66), 5 (bnl5.40), and 6 (umc85), and accounted for 24% of the phenotypic variation. Localized symptoms may reflect the amount of mite feeding or the extent of virus spread at the point of infection. Identification of cosegregating markers may facilitate selection for HPV and WSMV resistance in corn breeding programs

Imaging of the unstable plaque: how far have we got?

Rupture of unstable plaques may lead to myocardial infarction or stroke and is the leading cause of morbidity and mortality in western countries. Thus, there is a clear need for identifying these vulnerable plaques before the rupture occurs. Atherosclerotic plaques are a challenging imaging target as they are small and move rapidly, especially in the coronary tree. Many of the currently available imaging tools for clinical use still provide minimal information about the biological characteristics of plaques, because they are limited with respect to spatial and temporal resolution. Moreover, many of these imaging tools are invasive. The new generation of imaging modalities such as magnetic resonance imaging, nuclear imaging such as positron emission tomography and single photon emission computed tomography, computed tomography, fluorescence imaging, intravascular ultrasound, and optical coherence tomography offer opportunities to overcome some of these limitations. This review discusses the potential of these techniques for imaging the unstable plaqu

Importance of the right ventricle in valvular heart disease

The importance of the right ventricle as a determinant of clinical symptoms, exercise capacity, peri-operative survival and postoperative outcome has been underestimated for a long time. Right ventricular ejection fraction has been used as a measure of right ventricular function but has been found to be dependent on loading conditions, ventricular interaction as well as on myocardial structure. Altered left ventricular function in patients with valvular disease influences right ventricular performance mainly by changes in afterload but also by ventricular interaction. Right ventricular function and regional wall motion can be determined with right ventricular angiography, radionuclide ventriculography, two-dimensional echocardiography or magnetic resonance imaging. However, the complex structure of the right ventricle and its pronounced translational movements render quantification difficult. True regional wall motion analysis is, however, possible with myocardial tagging based on magnetic resonance techniques. With this technique a baso-apical shear motion of the right ventricle was observed which was enhanced in patients with aortic stenosi