1,721,057 research outputs found
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Data for Integration over discrete closed surfaces using the Method of Fundamental Solutions
Full text linkThe Method of Fundamental Solutions (MFS) is an established technique for solving linear partial different equations. In this paper it is used for a new purpose: the approximation of integrals over closed surfaces from a finite set of known points and values. The MFS is used to fit an implicit surface through the surface points, where the implicit equation is chosen such that a surface integral is provided by summing the weights of the fit. From the divergence theorem, these surface integrals can be related to specific integrals over the enclosed volume. As a demonstration, we calculate the surface area, volume, centroid and radius of gyration, for three solid geometries: a sphere, a torus, and an ellipsoid. Very quick convergence to analytical results is shown. Local surface properties, such as the components of curvature, can also be obtained accurately. The drawbacks and advantages of the method are discussed, and the potential to calculate properties of constant-density rigid bodies (e.g. the moment of inertia tensor) and averages of incompressible flow fields (e.g. average flow velocity and strain rate) is highlighted
Variations on the Author
Full text link“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
Full text linkWe 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
Numerical simulation of boundary-layer control using MEMS actuation
Full text linkMEMS actuators and their effect on boundary layers is investigated using numerical simulation. The thesis is specifically focussed on jet actuators and their application to the targeted control of turbulent boundary layers.
A complete numerical model of jet-type actuators, including the popular synthetic-jet actuator, is developed. The assumed input is the voltage signal to the piezocermic driver and the calculated output is the exit jet velocity. Thorough validation of the numerical code is presented and simulations performed to highlight the key issues in MEMS-actuator design.
The three-dimensional boundary-layer disturbance created by the MEMS actuator is modelled using a velocity-vorticity formulation of the Navier-Stokes equations. The parallel code is rigorously validated against results from linear stability theory and transitional-streak measurements. The boundary-layer code is used to determine a performance criterion for MEMS jets; it is shown that the net mass flow from a jet best determines its effectiveness. The code is also used to demonstrate the macro-scale capabilities of MEMS-scale actuators; a grid-scaling method is described and employed to facilitate this calculation.
A method is presented that enables high- and low-speed streaks to be modelled economically in otherwise undisturbed mean flows. Using this model, the fundamental principles of targeted control using MEMS actuation are explored.
The MEMS-actuator and boundary-layer models are coupled, and an investigation into the interactive effects of the two systems is described. Using the coupled code, disturbances in the boundary layer are shown to induce velocities in inactive devices. One special case occurs when an oscillating pressure field creates Helmhotz resonance within the cavity of a MEMS actuator, thus causing large mass flow rates in and out of the device. It is also suggested that the MEMS device could strongly interact with the random fluctuations of a turbulent boundary layer, leading to highly unpredictable actuator responses
First-order analysis of slip flow at the microscale and nanoscale
No full textA convenient approach to derive simple expressions for properties of Stokes
flows with low levels of slip is presented. The method is based on a series
expansion of a Stokes-flow solution (one satisfying a Navier slip boundary
condition) with non-dimensional slip length as the small expansion parameter.
Most notably, first-order predictions of surface moments of the traction force
(e.g., drag and torque) can be obtained purely from no-slip solutions to the
same problem. The analysis is directly applicable to microscale rarefied gas
flows in the so-called `slip regime' and relevant to a range of liquid flows at
the microscale and nanoscale. A number of application examples are considered,
with expressions derived for: the drag and torque on translating and rotating
Janus particles and spheroids (prolate and oblate); the efficiency of a micro
journal bearing; the speed of a self-propelled particle (a `squirmer'); and the
pressure drop required to drive flow through long, straight micro/nano
channels. Where appropriate, accurate numerical calculations provide
verification of the derived expressions. Certain general results are also
obtained. For example, for low-slip Stokes flow: any surface distribution of
positive slip length will reduce the drag on any translating particle; any
perimetric distribution of positive slip length will reduce the pressure loss
through a straight channel flow of arbitrary cross-section; unlike in no-slip
flows, the rate of work done by a bounding solid surface on the fluid is not
balanced by dissipation in the fluid volume -- there is additional dissipation
at the fluid-solid interface
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
High-resolution Burnett simulations of micro Couette flow and heat transfer
No full textA high-order continuum model for micro-scale flows is investigated. The Burnett equations are applied to the steady-state micro Couette flow of a Maxwellian monatomic gas. Solutions to these equations are shown to be stable for all Knudsen numbers (Kn) up to the limit of the equations' validity (Kn→1). The reason why previous researchers have failed to obtain solutions to this problem for Kn much greater than 0.1 is explained. A procedure is proposed to overcome these difficulties, and its application successfully demonstrated. Results are obtained on high-resolution numerical grids and show good agreement with data obtained from direct simulation methods. A reduced-order procedure is also described for calculating the implicitly defined first-order slip boundary conditions prior to the solution of the full equations. This method can be used to generate accurate initial guesses for an iterative solution. The comparative utility of second-order boundary conditions is explored and alternatives discussed
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