1,721,077 research outputs found
Design and Development of Hybrid Metal and Polymer Additive Manufacturing System
No full textAdditive manufacturing (AM) is a layer-based manufacturing process aimed at producing parts directly from a Computer-aided design (CAD) model. There are various types of AM systems, which can be classified based on: (i) the base material being used for fabrication, such as polymers, ceramics, and metals; (ii) indirect and direct processes depending on the bonding method; and (iii) the state of the input raw material, i.e., liquid, molten, powder, and solid layer. The current research in AM processes includes technology development for the printing of multi-material parts using two or more materials such as metal, polymer, glass, ceramics, and graphene. The multi-material additive manufacturing (MMAM) processes are complex and challenging due to the significant differences in material deposition techniques, material processing temperature, or pre/post-processing methods involved for an individual material. Our work focuses on the hybrid metal/polymer printing process where liquid metal printing is achieved using a novel design of a molten metal droplet-on-demand (MMDoD) system. The metal is fed into the MMDoD system in the form of solid wire and is melted using a zero-voltage-switching circuit based induction heater. The magnetic field, eddy current density, and power transfer from the induction coil to the molten metal pool are studied using experiments, theoretical formulation, and FEM simulations. The influence of workpiece geometry on the induction heating process is also studied for solder alloy and aluminum billets. These studies show that for a given geometry of induction coil and workpiece, the power transferred to the workpiece is a non-monotonic function of the workpiece’s resistivity. Also, the heating rate of the workpiece depends on the thermal mass and the magnetic field flux in and around the workpiece. Using these studies, the resistivity of the workpiece, and the geometry of the workpiece and induction coil, can be chosen to achieve faster heating and melting of the metal.
Once the raw material is in the liquid state, it can be used to generate molten metal droplets (MMDs). To generate the MMD, a novel MMDoD system is designed and developed using a thermally insulating piston and magnetostrictive actuator. Using the MMDoD mechanism, the molten metal is deposited on the printing bed surface (glass) or partially formed part (metal or polymer – PLA/ABS). To find the optimal parameters of MMD generation process, a parametric study of the MMDoD mechanism is conducted by varying the size and material (Brass, Stainless-Steel, Nickel-plated steel alloy) of the nozzle, the gap between nozzle and piston, unfiltered vs. low-pass filtered actuation pulse, and the actuation pulse amplitude. This shows the following regions where, DoD process is not achieved, and the DoD is achieved with the generation of single or multiple droplets for each actuation. The droplet size, Feret width and length, and standard deviation are measured using snapshots from the high-speed camera of the droplet formation process. The region where a single MMD is generated for each actuation of the MMDoD mechanism with the least standard deviation is most desirable for the reproducible metal AM process. A parametric study is conducted to find the optimal printing parameters of the metal AM system by varying the gap between each droplet to print the 2D connected metal lines on the substrate. Other parameters like the size of MMDs, droplet ejection rate (20Hz), and liquid metal temperature are kept fixed. The 3D metal printing can be achieved by printing these metal lines layer-by-layer.
MMDoD system is extended to multi-material additive manufacturing (MMAM) system by combining it with polymer extrusion system. The designed MMAM system consists of a controller board to control the overall system, an induction heater, a computer numeric control (CNC) build platform/positioning system, MMDoD mechanism, and the polymer extruder. The system is designed and developed to print metal (Solder alloys - Sn99Cu1, Sn63Pb37, and Sn96.5Ag3.5) with polymer (PLA and ABS). To demonstrate the hybrid AM of metal and polymer, a few mechanical structures (2D planar text, hollow tube, hollow square pyramid, hollow hexagon) and electronic device (RC-LED circuit) are fabricated. The deposition of molten metal on polymer substrate leads to good bonding of metal on polymer due to remelting of the polymer surface. The working of the printed, electronic device is tested and found satisfactory. The testing is conducted by checking the electrical connectivity along the track and the functionality of the electronic device by measuring the output signal waveform. In the future, the combined metal and polymer AM system can be combined with a pick-and-place mechanism that can help achieve a rapid AM of functional 3D electronic devices
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
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
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
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
Curr Opin Pediatr
Full text linkPurpose of reviewMetals play major roles in children's health and are associated with negative health outcomes via deficiency, overload or toxicity. Constantly evolving analytical technology can provide new insight into how metal metabolism and exposure biology are intertwined in a range of biological matrices.Recent findingsExposure can occur prenatally as many metals cross the placental barrier. The placenta is permeable to many metal species, some through tightly regulated transporters, and others because of a limited capacity for detoxification. Post-birth, metal exposure continues to exert long-term health effects, ranging from exposure to exogenous heavy metals, such as lead, to overload of otherwise essential metals, including manganese. Increasing evidence supports the existence of critical developmental windows when susceptibility to toxicants and nutritional deficiencies is highest. Elemental imaging technology provides micro-spatial information on metal uptake and retention across tissue architecture, which provides important insights into exposure and biologic response.SummaryImaging the spatial distribution of elements, both essential and toxic, provides information that bulk measures cannot, including cell-specific distributions and timing of exposure.DP2 ES025453/ES/NIEHS NIH HHS/United StatesR00 ES019597/ES/NIEHS NIH HHS/United StatesDP2ES025453/DP/NCCDPHP CDC HHS/United StatesR00ES019597/ES/NIEHS NIH HHS/United State
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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