196,231 research outputs found
A Novel Tomographic Characterisation Approach for Sag and Dross Defects in Metal Additively Manufactured Channels
No full textChannels and bores in metal components produced by laser powder bed fusion (LPBF) are internal features that are typically affected by defects such as dross and sag formation, dimensional errors and global deformations in different proportions. Such deviations from the ideal geometry may strongly limit the functionality of the channels, but are difficult to prevent, due to complex multi-physical production aspects. Different destructive and non-destructive approaches are available to investigate the geometry of the internal features and possibly correlate their results to the LPBF process parameters; however, such approaches do not offer a systematic method to derive key characteristics of the main contributors for channel deviations. Hence, this work proposes a novel tomographic non-destructive analysis of LPBF channels and bores, focusing on the derivation of sag and dross key parameters. The methodology works on polar-transformed profiles obtained from image stacks which are extracted perpendicularly to the channel axis from the X-ray computed tomography (CT) reconstructed volume. The method allows for the clear determination of surface characteristics and includes the quantitative evaluation of descriptors through an algorithm specifically developed for the purpose. In particular, general form deviations are addressed by fitting sinusoidals on the unwrapped mean surface profile, to tackle deviations induced by thermal residual stresses. Proposed descriptors of sag and dross are the onset angle of protrusions, separation criteria between sag and dross effects, and the peak analysis of the mean profile after approximation with a least squares spline. The developed algorithm is tested in the case study of a LPBF AlSi7Mg0.6 benchmark part comprising hollow cylinders and inter-connecting frusta with different diameters. The resulting evaluation of the benchmark part also corroborates how the proposed methodology can help to obtain more precise information regarding the correlation of LPBF fabrication conditions and obtained channels geometrical deviations. Furthermore, the results show possible routes to enable an a-priori compensation of the nominal channel design for first-time right LPBF manufacturing.sponsorship: This research was funded by the EU Framework Programme for Research and Innovation -Horizon 2020 -Grant Agreement No 721383 within the PAM2 (Precision Additive Metal Manufacturing) research project. Umberto Paggi and Lore Thijs (3D Systems) are kindly acknowledged for the fabrication of the spyglass benchmark at the 3D Systems Leuven facilities. (EU Framework Programme for Research and Innovation -Horizon 2020 within the PAM2 (Precision Additive Metal Manufacturing) research project|721383)status: Published onlin
Unravelling the dependency of dross formations in metal additively manufactured channels as a function of channel diameter and inclination angle
No full textIn recent years, the non-destructive characterisation via X-ray computed tomography of internal features, often produced with novel manufacturing methods, has gained increasing attention. Reducing the rate of defects during the production of internal features is of particular interest since post-processing steps are highly cumbersome, or removal of defects is, in many cases, even impossible for complex channels or bores. However, it is not sufficient to characterise the defects solely, but their root causes need to be understood in depth to allow for a-priori compensation approaches fostering first-time right part production. To achieve this, it is imperative to fully understand the connections and influences between the different factors, to enable the creation of versatile and scalable correction and compensation approaches. Within this scope, this work presents a characterisation of additively manufactured internal channels, focussing on dross defects encountered in overhang regions of the channel and their dependency as a function of a broad range of channel diameters and inclination angles. The extraction of the required information from the channels is based on cross-sectional images along the channel’s axis of the reconstructed 3D volume, obtained with high-resolution X-ray computed tomography. With the data obtained through an analysis algorithm presented in an earlier publication, it is possible to extract characteristic identifiers that can be used to calculate potential compensations counteracting the defects emerging during the printing. With the aid of these identifiers, it is possible to chart out general trends of the channel defects as a function of channel diameter and inclination angle. Therefore, the results allow to identify parameters where certain defects remain almost constant for a variation of the channel diameter.sponsorship: This research was funded by the EU Framework Programme for Research and Innovation-Horizon 2020-Grant Agreement No 721383 within the PAM2 (Precision Additive Metal Manufacturing) research project. (EU Framework Programme for Research and Innovation-Horizon 2020|721383)status: Publishe
Activity of the (R)-Enantiomers of 9-(2-phosphonylmethoxypropyl)-adenine and 9-(2-phosphonylmethoxypropyl)-2,6-diaminopurine against human immunodeficiency virus in different human cell systems
No full textThe (S)- and (R)-enantiomers of 9-(2-phosphonylmethoxypropyl) derivatives of adenine (PMPA) and 2,6-diaminopurine (PMPDAP) were evaluated for their inhibitory effect on HIV replication in several human cell systems, including natural peripheral blood lymphocytes (PBL) and freshly isolated monocyte/macrophages (M/M). The (R)-enantiomers of PMPDAP and PMPA were ~10- to 100-fold more effective against HIV than their (S)-enantiomeric counterparts. The antiviral efficacy of (R)-PMPA was comparable to that of the prototype acyclic nucleoside phosphonate 9-(2-phosphonylmethoxyethyl)adenine (PMEA). The most potent and selective HIV inhibitor was (R)-PMPDAP. Its 50% effective concentration ranged from 0.01 μM for HIV-1/Ba-L in M/M to 1-2.8 μM for HIV-1/III(B), and HIV-1/HE in C8166, GEM, Molt/4, MT-4 and PBL cells. Both (R)-PMPA and (R)-PMPDAP were not toxic to the host cells at 300 μM
Anti-HIV-1 activity of combinations and covalent conjugates of negatively charged albumins and AZT
No full textPharmacophore modeling and molecular docking led to the discovery of inhibitors of human immunodeficiency virus-1 replication targeting the human cellular aspartic acid-glutamic acid-alanine-aspartic acid box polypeptide 3
No full textHIV-1 replication has been inhibited by using a compound able to target the human cellular cofactor DEAD-box ATPase DDX3, essential for HIV-1 RNA nuclear export. This compound, identified by means of a computational protocol based on pharmacophoric modeling and molecular docking calculations, represents the first small molecule with such a mechanism of action and could lay the foundations for a pioneering approach for the treatment of HIV-1 infections. © 2008 American Chemical Society
Dr. Duane M. Jackson, Morehouse College, July 2011
No full textThis video is a conversation with Dr. Duane M. Jackson. Dr. Jackson talks about his paper, "Recall and the Serial Position Effect: The Role of Primacy and Recency on Accounting Students' Performance." Jackie Daniel, AUC Woodruff Library, is the interviewer
Anti-HIV-1 activity of combinations and covalent conjugates of negatively charged albumins and AZT
No full textAnti-HIV-1 activity of combinations and covalent conjugates of negatively charged albumins and AZT
No full text"Reflections on the subject of Emigration from Europe with a view to Settlement in the United States" By M. Carey.
No full text"Reflections on the subject of Emigration from Europe with a view to Settlement in the United States: containing bried sketches of the moral and political character of those states.
By M. Carey, member of the American philosophical, and of the American Antiquarian Society, and author of The Olive Branch, Cindiciae Hibernicae, essays on banking, on political economy, and on internal improvement.
To which are now added the English editor's comments on the subject; together with Important Advice to Emigrants, and Cautions Against Impositions Practiced in the Outports
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
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