124,685 research outputs found
Acoustic properties of additive manufactured porous material
No full textAcoustic porous materials are extensively used in many engineering applications like building, automobile, aviation, and marine. The health risk factor and environmental claims, associated with traditional materials such as glass wool, mineral fibers, and polymer foams demand for the alternative porous acoustic absorbing materials. Advances in additive manufacturing (AM) allow to manufacture complex structures and give an alternative method to produce porous materials. This study investigates the acoustic properties of porous sound-absorbing material produced by using additive manufacturing (AM) technique and explores the feasibility of AM to manufacture acoustic absorptive materials. For study, three samples with different aperture ratios were fabricated by AM technique, and their sound absorption coefficients were measured experimentally by using the impedance tube. The theoretical formulation for predicting normal sound absorption coefficient of sample with and without air gap was developed and compared with experimental results. The predicted absorption coefficient agrees well with measured results. The measured results indicate that the absorption coefficient of the structures fabricated through AM can be altered by varying aperture ratio and air gap behind the sample. This study reinforces the capability of AM for producing complex acoustic structures with better acoustic properties
Acoustic characterization of additive manufactured micro-perforated panel backed by honeycomb structure
No full textThis paper studies the acoustic properties of an additive manufactured micro-perforated panel backed by a periodic honeycomb structure. Extrusion-based Fused Filament Fabrication (FFF) technique of Additive Manufacturing (AM) is used. Absorption coefficient of the proposed structure is measured using an Impedance tube. An analytical model is developed to predict the acoustic absorption coefficient. The analytical results are compared with the experimental results and a good agreement is observed between them. A parametric study is conducted to understand the effect of perforated hole size on the absorption coefficient and peak frequency
Acoustic characterization of additive manufactured layered porous materials
No full textIn the present study, acoustic properties of layered porous materials produced by Fused Filament Fabrication (FFF) technique of Additive Manufacturing (AM) have been investigated. The porous materials are fabricated by using different infill percentage of materials in the direction of fabrication, which leads to layered porous material of various pore sizes along the direction of fabrication. Samples with different combinations of infill percentages are fabricated, and their sound absorption coefficient is measured by using two microphone impedance tube technique. Measured results indicate that the sound absorption coefficient of additive manufactured porous materials can be tuned to the required frequency range by changing the combination of infill percentages. The results and fabrication technique presented here gives an alternative method to fabricate layered porous materials
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
Acoustic properties of additive manufactured narrow tube periodic structures
No full textQuarter tube periodic resonators are used to attenuate the acoustic energy of discrete frequencies wherein their sizes can vary from narrow to large. This paper reports acoustical properties of additive manufactured, narrow tube, single and multi-periodic structures, both, theoretically and experimentally. Herein, multi-periodic structures are defined as periodically arranged unit sections of tubes, where each section is composed of periodically repeated unit cells of different sizes and shapes. Structures with hexagonal narrow tubes and octagonal narrow tubes with interfacial gaps are considered for the study, and normal absorption coefficients of these samples are measured by using impedance tube. the theoretical absorption coefficient of these structures is predicted using unit section analysis method and narrow tube theory, where shape dependent viscous and thermal losses are incorporated. Estimated theoretical absorption coefficients are in good agreement with measured results. The result shows that the frequency and amplitude of maximum absorption can be varied by altering the aperture ratio and/or the length of periodic structure. The proposed theoretical method gives an alternative approach for designing and manufacturing periodic narrow tubes for different applications such as absorbing panels, acoustic transducers, and engine filter elements
Dispelling the Myths Behind First-author Citation Counts
No full textWe 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
Acoustic characterization of additive manufactured perforated panel backed by honeycomb structure with circular and non-circular perforations
No full textThis paper studies the acoustic properties of an additive manufactured micro-perforated panel backed by a periodic honeycomb structure. Extrusion-based Fused Filament Fabrication (FFF) technique of Additive Manufacturing (AM) is used to fabricate the integrated honeycomb structures with a perforated face sheet. Normal absorption coefficient of the fabricated structure is measured in impedance tube using two microphone transfer function method. A generalized analytical formulation based on unit section analysis applicable to various cross sections of perforations has been proposed to predict the absorption coefficient, where shape dependent viscous effects in the perforation are incorporated by deriving effective complex density of the medium. To study the effect of perforation shape, three geometries viz., circular, triangular and square perforations are considered for analysis where triangular shape found to have more absorption coefficient and lower frequency of peak absorption. In addition, broadband absorption coefficient of proposed structure has been demonstrated by deploying hexagonal cells of different lengths in a unit section. The analytical results are compared with experimental results and a good agreement is observed between them. A parametric study is conducted to understand effect of perforated hole size and cell length on the absorption coefficient and peak frequency. Results show that the proposed structures can be tuned to desired frequency range by altering geometric parameters like cell length, shape and size of perforation hole. Technique and methodology presented in the current study gives an alternative way to design and fabricate honeycomb structures with perforations for acoustic applications such as aircraft cabins, ship structures and building acoustics
Acoustic measurement of additive manufactured concentric tube reverse flow resonators
No full textThis study investigates acoustic properties of additive manufactured (AM) concentric tube reverse flow (RF) resonators where acoustic attenuation with smaller sample length is achieved by increasing effective travel length of acoustic waves within a structure. The theoretical modeling based on narrow tube theory has been proposed to predict absorption coefficient, while numerical estimation of absorption coefficient is carried out using finite element method (FEM). The predicted theoretical and numerical results are found to be in good agreement with measured results in impedance tube, thus demonstrating its potential in achieving low frequency attenuation with compact size structures
Pragmatic Case Studies as a Source of Unity in Applied Psychology
No full textTo unify or not to unify applied psychology: that is the question. In this article we review pendulum swings in the historical efforts to answer this question—from a comprehensive, positivist, “top-down,” deductive yes between the 1930s and the early 60s, to a postmodern no since then. A rationale and proposal for a limited, “bottom-up,” inductive yes in applied psychology is then presented, employing a case-based paradigm that integrates both positivist and postmodern themes and components. This paradigm is labeled “pragmatic psychology” and, its specific use of case studies, the “Pragmatic Case Study Method” (“PCS Method”). We call for the creation of peer-reviewed journal-databases of pragmatic case studies as a foundational source of unifying applied knowledge in our discipline. As one example, the potential of the PCS Method for unifying different angles of theoretical regard is illustrated in an area of applied psychology, psychotherapy, via the case of Mrs. B. The article then turns to the broader historical and epistemological arguments for the unifying nature of the PCS Method in both applied and basic psychology.Peer reviewe
Dr. Edwin Wright Collection: Author Unknown
No full textNotes - The author relates several short stories about his neighbours including Alex McDonell, homesteading and life around Meanook and Athabasca (1 page
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