Laboratory measurements of air flow over wind waves following the moving water surface

CER68-69PcC18.December 1968.Includes bibliographical references.This dissertation presents a laboratory study of the dynamic properties of air flow over small wind-generated water waves. Through the measurements of mean velocity profiles, turbulent fluctuation profiles and energy spectra, the detailed structure of turbulent wind immediately above and between the crests of progressive water waves has been examined. A self-adjusting probe positioner was designed, which allowed a velocity sensor (a hot wire anemometer) to measure instantaneous air velocities at a fixed distance from a moving water surface with waves of a dominant frequency, 2 to 3 Hz. With the aid of a digital computer, the desired parameters of air flow were obtained by a statistical technique which was developed to sample and average simultaneous recordings of water surface displacements and instantaneous air velocities. The statistical properties of water surface which include wave spectra, probability distributions of water surface elevation and its time derivatives, give good agreement with the results obtained by previous investigators. The waves investigated have the ratio of wave celerity and air friction velocity on the average close to one. For those waves the effect of the moving surface seems to cause little deviation on the dynamic properties of the velocity field from those found over solid boundaries. Mean properties of the turbulent air flow referred to the mean water level were obtained by continuous sampling of the air flow over many waves with a sensing probe either at a fixed distance from the mean water level (fixed probe measurement) or at a constant distance from the moving water surface (moving probe measurement). It was found that for continuously averaged measurements the fixed probe yielded results which deviate less from the local mean than the moving probe results. This holds for the mean velocity distributions and especially for the turbulent quantities. The results of local air properties indicate that, on the average, air flow separates from the wavy water surface just behind crests and reattaches somewhere on the windward face of the next wave. The measured turbulent quantities consistently show the characteristics of a separated air flow. The separation phenomenon suggests that, without some modification, the Benjamin-Miles' shearing flow mechanism is inapplicable to the growth of fully developed small water waves. The observed flow configuration tends to support the separation mechanism of energy transfer originally outlined by Jeffreys, and later explored further by Stewart. This study demonstrates the usefulness of using a wave following probe to obtain a more complete description of the dynamic properties of both air and water near the interface. In principle, the methods developed here could be used to further explore the properties of air flow over undulating surfaces, including the determination of the local Reynolds stresses

Efficiency and Returns to Scale Measurements with Shared Inputs in Multi-Activity Data Envelopment Analysis: An Application to Farmers' Organizations in Taiwan

This paper addresses the question how team production promotes efficiency of a firm when some inputs can be rewarded on the basis of outputs but some cannot because they are shared among outputs and non-separable. A multi-activity DEA model with variable returns to scale is proposed to provide information on the efficiency performance for organizations with inputs shared among several closely related activities. The model is applied to study the case of 279 farmers' associations in Taiwan. The result suggests that it is important to improve the efficiency of the non-profit oriented activities to improve their overall performances. Three out of four departments of TFAs can gain from economies of scale through expansion, while the remaining one gains through contraction. Thus, policies promoting structural adjustment and consolidations of TFAs would not be inconsistent with public interests.multi-activity DEA, shared inputs, efficiency measure, directional distance function, Productivity Analysis,

SK channels and ventricular arrhythmias in heart failure

Small-conductance Ca2+-activated K+ (SK) currents are important in the repolarization of normal atrial (but not ventricular) cardiomyocytes. However, recent studies showed that the SK currents are upregulated in failing ventricular cardiomyocytes, along with increased SK channel protein expression and enhanced sensitivity to intracellular Ca2+. The SK channel activation may be either antiarrhythmic or proarrhythmic, depending on the underlying clinical situations. While the SK channel is a new target of antiarrhythmic therapy, drug safety is still one of the major concerns

Productivity Change in Taiwan's Farmers' Credit Unions: A Nonparametric Risk-Adjusted Malmquist Approach

This article proposes an extended three-stage DEA methodology similar to Fried et al. (2002) to improve the measurement of productivity growth then the assumption of free disposability of undesirable outpu t does not apply. A directional distance function is used to construct adjusted Malmquist-Luenberger productivity indexes which simultaneously account for the impacts of undesirable outputs, environmental variables, and statistical noise. Panel data for 264 farmers' credit unions (FCUs) in Taiwan covering the 1998-2000 period are employed to illustrate the advantages of this method. On average, the productivity of Taiwan's FCUs is found to have deteriorated over the 1998-2000 period. Although an improvement in efficiency has been observed, the major reason for the deterioration is found to be due to the regression of techno logy.Malmquist-Luenberger productivity index, three-stage DEA, undesirable outputs, directional distance function, Agricultural Finance, Productivity Analysis,

Mechanism of thermal field and electric field in resistive random access memory using the high/low-k side wall structure

In the Internet of things (IoT) era, low power consumption memory will be a critical issue for further device development. Among many kinds of next-generation memories, resistive random access memory (RRAM) is considered as having the most potential due to its high performance. To prevent unrecoverable hard break-down of a RRAM device, the RRAM should be collocated with a transistor for external current compliance. With decreasing device cell size, however, the operating voltage of the transistor will become smaller and smaller. Previous study has determined that the forming voltage of RRAM increases when device cell size is reduced, which is a very crucial issue especially when the device is scaled down. We have proposed a high-k sidewall spacer structure in RRAM to solve the dilemma of increasing forming voltages for device cell scaling down. Based on the COMSOL-simulated electrical field distributions in the high-k RRAM. In addition, thermal conductivity of sidewall spacer influenced resistive switching behavior. Suitable thermal conductivity of sidewall materials can enhance resistive switching behavior. Please click Additional Files below to see the full abstract