1,721,023 research outputs found
Acoustic damping and aeroacoustic instabilities of cavities subject to bias and grazing flows
No full text
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
Large Eddy Simulation of cross-flow around a square rod at incidence with application to tonal noise prediction
Get PDFWe consider the prediction of the flow around a square rod as a generic bluff body at low Mach number (below 0.3) and high Reynolds number (above 5000) and the corresponding tonal noise. Instability of such flow is crucial for potential mechanical vibrations and noise production. Due to the presence of sharp edges the flow separation along a square rod is relatively easy to predict. The flow remains however quite complex as it involves re-attachment and secondary vortex shedding. Depending on the angle of attack, between the main flow direction and the bottom side wall of the rod, three flow types are observed. Firstly at low angles of attack the flow separating from both upstream edges forms a periodic vortex street in the wake. Secondly above a critical angle of attack around 13o, the flow re-attaches to the bottom side wall. The wake is dominated by vortex shedding from the upper front edge and the lower downstream edge. At 45o the stagnation point is on the front edge and flow separation occurs from the two lateral edges. In the literature the wake is reported to display a von K`arm`an vortex street corresponding to a whistling mode. For angle of attack between 25o and 45o, we observe experimentally a second mode in which the wake is stable and the rod does not whistle. We call this the silent mode. One can switch from one mode to the other by perturbing the flow in front or behind the rod. Direct Numerical Simulation of the radiated sound is extremely difficult and certainly not feasible for industrial applications. We assess the potential of a hybrid method in which the flow is modelled by means of an incompressible Large Eddy Simulation (LES). The flow data is then used to estimate the sound radiation by using the Lighthill-Curle aeroacoustical analogy. Incompressible resolved LES obtained with a commercial code provides a fair prediction of the flow if the full length of the rod is taken into account including the side walls used to support the rod in the experiments. Combining the LES results with the aero-acoustical analogy provides a prediction of observed tonal noise within 2 dB. The prediction of broad band noise was not considered. The use of quasi two-dimensional LES calculations or two-dimensional Unsteady-Reynolds Averaged Navier Stokes (URANS) models appears to be much less accurate. These LES calculations are unfortunately still much too demanding to allow a systematic parametric study. They also do not capture the observed silent mode
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
Experimental Investigations of Bassoon Acoustics
Get PDFThe bassoon is a conical woodwind instrument blown with a double-reed mouthpiece. The sound is generated by the periodic oscillation of the mouthpiece which excites the air column. The fundamental frequency of this oscillation is determined to a large extent by the resonances of the air column. These can be varied by opening or closing tone-holes. For any given tone hole setting a fine-tuning in pitch is necessary during playing. Musicians adjust the slit opening of the double-reed by pressing their lips against the opposing reed blades. These so-called embouchure corrections are required to tune the pitch, loudness and sound color of single notes. They may be tedious, especially if successive notes require inverse corrections. However, such corrections are essential: Due to the very high frequency sensitivity of the human ear playing in tune is the paramount requirement when playing music. This implies, that embouchure actions provide an important insight into a subjective quality assessment of reed wind instruments from the viewpoint of the musician: An instrument requiring only small corrections will be comfortable to play.
Theoretical investigations of the whole system of resonator, reed, and musician by use of a physical model nowadays still seem insufficient with respect to the required precision. Therefore the path of well-described artificial mouth measurements has been chosen here. For the separate treatment of the resonator and the double-reed, existing classical models have been used. Modifications to these models are suggested and verified experimentally. The influence of the musician is incorporated by the lip force-dependent initial reed slit height. For this investigation a measurement setup has been built that allows precise adjustment of lip force during playing. With measurements of the artificial mouth parameters blowing pressure, mouthpiece pressure, volume-flow rate and axial lip position on reed, the experiment is fully described for a given resonator setting represented by an input impedance curve. By use of the suggested empirical model the adjustment parameters can be turned into model parameters. A large data set from blowing experiments covering the full tonal and dynamical range on five modern German bassoons of different make is given and interpreted.
The experimental data presented with this work can be a basis for extending the knowledge and understanding of the interaction of instrument, mouthpiece and player. On the one hand, they provide an objective insight into tuning aspects of the studied bassoons. On the other hand the experiments define working points of the coupled system by means of quasi-static model parameters.
These may be useful to validate dynamical physical models in further studies. The experimental data provide an important prerequisite for scientific proposals of optimizations of the bassoon and other reed wind instruments. It can further serve as a fundament for the interdisciplinary communication between musicians, musical instrument makers and scientists.:1 Introduction 1
1.1 Motivation 1
1.2 Scientific Approaches to Woodwind Musical Instruments 3
1.3 Organization of the Thesis 6
2 Acoustical Properties of the Bassoon Air Column 7
2.1 Wave propagation in tubes 7
2.1.1 Theory 7
2.1.2 Transmission Line Modeling 8
2.1.3 Implementation 18
2.1.4 Remarks on Modeling Wall Losses in a Conical Waveguide 19
2.2 Input Impedance Measurement 23
2.2.1 Principle 23
2.2.2 Device 23
2.2.3 Calibration and Correction 24
2.3 Comparison of Theory and Experiment 27
2.3.1 Repeatability and Measurement Uncertainty 27
2.3.2 Comparison of numerical and experimental Impedance Curves 32
2.4 Harmonicity Analysis of the Resonator 35
2.4.1 The Role of the Resonator 35
2.4.2 The reed equivalent Volume 35
2.4.3 Harmonicity Map 36
2.5 Summary 38
3 Characterization of the Double Reed Mouthpiece 41
3.1 Physical Model of the Double-Reed 41
3.1.1 Working Principle 41
3.1.2 Structural Mechanical Characteristics 42
3.1.3 Fluid Mechanical Characteristics 44
3.2 Measurement of Reed Parameters 49
3.2.1 Quasi-stationary Measurement 49
3.2.2 Dynamic Measurement 50
3.3 Construction of an Artificial Mouth 52
3.3.1 Requirements Profile 52
3.3.2 Generic Design 53
3.3.3 The artificial Lip 54
3.3.4 Air Supply 55
3.3.5 Sensors and Data Acquisition 57
3.3.6 Experimental setup 59
3.4 Summary 59
4 Modeling Realistic Embouchures with Reed Parameters 61
4.1 Reed Channel Geometry and Flow Characteristics 61
4.1.1 The Double-Reed as a Flow Duct 61
4.1.2 Bernoulli Flow-Model with Pressure Losses 65
4.1.3 Discussion of the Model 68
4.2 Quasi-static Interaction of Flow and Reed-Channel 72
4.2.1 Pressure-driven Deformation of the Duct Intake 72
4.2.2 Reed-Flow Model including Channel Deformation 75
4.2.3 Influence of Model Parameters 76
4.2.4 Experimental Verification 78
4.3 Effect of the Embouchure on the Reed-Flow 81
4.3.1 Adjustment of the Initial Slit Height 81
4.3.2 Quasi-static Flow in the Deformed Reed-Channel 83
4.3.3 Simplified empirical Model including a Lip Force 85
4.4 Summary 93
5 Survey of Performance Characteristics of the Modern German Bassoon
5.1 Experimental Procedure and Data Analysis 95
5.1.1 Description of the Experiment 95
5.1.2 Time Domain Analysis 97
5.1.3 Spectral Analysis – Period Synchronized Sampling 98
5.1.4 Spectral Centroid and Formants 99
5.1.5 Embouchure parameters 100
5.2 Observations on the Bassoon under Operating Conditions 105
5.2.1 Excitation Parameter Ranges 106
5.2.2 Characteristics of the radiated Sound 110
5.2.3 Reed Pressure Waveform Analysis 115
5.2.4 Summarizing Overview 118
5.3 Performance Control with the Embouchure 120
5.3.1 Register-dependent Embouchure Characteristics 120
5.3.2 Intonation Corrections 123
5.3.3 Sound Color Adjustments 127
5.3.4 Relation to the acoustical Properties of the Resonator 129
5.4 Summary 137
6 Conclusion 139
6.1 Summary 139
6.2 Outlook 14
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
- …
