1,721,238 research outputs found
Numerical investigation of ventilated cavitating flow in the wake of a circular cylinder
No full textVentilated cavitating flow of a circular cylinder is investigated by numerical simulation. The coupled level set and volume of fluid method is used to capture the interface between the cavity and surrounding water. The simulation results indicate that the bubble size distribution in the wake is closely related to the turbulence intensity. The bubble number reaches its peak value in the closure region owing to the high turbulence intensity there. When the gas entrainment coefficient Q(v) increases, the length of the cavity increases and the turbulent kinetic energy decreases, leading to a decrease in the bubble number and an increase in the Sauter mean diameter. It is also found that the presence of the ventilated cavitation delays the formation of vortices and affects the vortex shedding. In the single phase flow, the enstrophy is concentrated in the shear layer and closure region. In the ventilated cavitating flow, on the other hand, the enstrophy is mainly distributed at the cavity interface and the re-entrant region, which indicates that the instability of the cavity interface and the existence of the re-entrant jet play important roles in the formation of vortices.</p
Performance maximization of actively managed funds
No full textA growing literature suggests that, even in the absence of any ability to predict returns, holding options on the benchmarks or trading frequently can generate positive alpha. The ratio of alpha to its tracking error appraises a fund's performance. This paper derives the performance-maximizing strategy, which turns out to be a variant of a buy-write strategy, and the least upper bound on such performance enhancement. If common equity indices are used as benchmarks, the potential alpha generated from trading frequently can be substantial in magnitude, but it carries considerable risk. The statistical significance in estimated alpha is low, and the probability of a negative alpha is high. The performance enhancement from holding options can be significant - both economically and statistically - if the options' implied volatilities are higher than the volatilities of the benchmark returns. The performance-maximizing strategy derived in this paper is different from the strategies that switch portfolio exposure to the benchmarks. The exposure-switching strategies are not promising unless the switching is based on superior information
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Integration of Remote Sensing, GIS and GPS techniques for dynamic monitoring of land resources in mountainous areas - A case study of Renhe District, Sichuan, China
No full textGeometric and radiometric correction, image processing, information extraction and the integration of remote sensing, GIS and GPS in the specific approach for dynamic monitoring of land resources in mountainous areas are discussed. A synthesized method combining the image difference approach with comparison post classification is employed and a monitoring system based on remote sensing, GIS and GPS are set up. Different illumination conditions are key factors influencing the spectral features in mountainous areas, thus the comprehensive analysis of DEM and NDVI are employed to restrain the influence of terrain. Errors also commonly generate in the registration of different temporal images and much change information is usually lost when the mean-value smoothing template is employed in the image processing in mountainous areas. To reduce the information lost, a regional auto-adaptive smoothing template is employed. As a case study, according to the specific characteristics of mountainous areas, the TM images acquired from both 1994 and 1996 are processed for land change detection in Renhe District, Sichuan. Field experiments for radiometric correction are conducted in the areas of 25 Km(2) in this district. The changed areas are precisely surveyed and validated after the fieldwork in which the database of detailed land survey is acquired. Combined with Geological Information System (GIS) technology and Global Position System (GPS), a 3S-based dynamic monitoring system of land resources change information in Renhe District is established, which helps the data renewal and daily management. Finally, the key factors influencing the accuracy of information extracting in mountainous areas are discussed.Remote SensingImaging Science & Photographic TechnologyEICPCI-S(ISTP)
The mechanism of surface-seal splash during water entry
No full textWhen a solid body impacts quiescent water at a certain velocity, the resultant surface-seal splash deforms and closes above the free surface. This study investigates the dynamics of the surface-seal splash by using a high-speed camera and particle image velocimetry (PIV) measurements. Based on PIV, an analytical model is developed to understand the mechanics of the surface-seal splash. The results indicate that the theoretical splash shapes are consistent with the experimental results. In addition, the effects of gravity, drag, surface tension, and aerodynamic pressure on the dynamics of surface-seal splash are also assessed, and the results indicate that the aerodynamic pressure plays a dominant role in the formation of the surface-seal splash.</p
An investigation on strain/stress distribution around the overlap end of laminated composite single-lap joints
No full textThe damages of laminated composite single-lap joints often begin from their overlap ends because strain/
stress concentrations often occur at the overlap ends. This paper presents the results of a combined
experimental and finite element (FE) investigation on the strain/stress distributions around the overlap
ends of laminated composite single-lap joints. Digital image correlation (DIC) technique is used to measure the strain fields near the overlap ends. A three-dimensional geometrically nonlinear FE model based
on the submodel technique is developed to predict the deformation of single-lap joints. A reasonable
agreement is achieved between the results from experimental measurements and FE analysis. Additionally, some FE models are built to investigate the effects of the mesostructures at the overlap ends on the
stress concentrations around the overlap end
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