186,459 research outputs found
THE INFLUENCE OF LASER POWER AND SCAN SPEED ON THE MICROSTRUCTURE, DISTORTIONS, AND MECHANICAL PROPERTIES IN THE L-PBF OF Ti-6Al-4V
No full textLaser powder bed fusion (L-PBF) has gained a lot of interest for its ability to build complex geometries with freedom of design. The wrong choice of process parameters like laser power (P) and scan speed (v) can result in parts with low ductility, pores, and distortion. In the literature, the influence of P and v on the quality of the printed part in terms of porosity defects, distortion, and mechanical properties has been widely explored. However, to obtain functional parts without defects it is crucial to consider different aspects simultaneously. This paper aimed to fill the lack of knowledge in the literature about the combined effect of laser power and scan speed on microstructure and distortions and their influence on mechanical properties. In this frame, tensile tests, microstructural, density, and distortion measurements were carried out to study the effect of P and v on mechanical strength, ductility, density, and distortion for Ti-6Al-4V parts produced with L-PBF. Three levels of P and v were analyzed in a range of 340-380 W and 1400-1600 mm/s, respectively. From the experimental analysis, a big influence of P on the ultimate tensile strength (UTS) and density was observed. Ductility, instead, was more affected by the v. Overall, high P and v resulted in significant distortions due to the increase in thermal gradient and cooling rate. Furthermore, porosity acted as a stress-relieving factor, and as a consequence, samples with high porosity showed less distortion
Relationship between pp65 antigenemia levels and real-time quantitative DNA PCR for Human Cytomegalovirus (HCMV) management in immunocompromised patients
No full textAbstract Background Quantitative real-time PCR assays, which are more rapid and practical than pp65 antigenemia determination, are progressively becoming the preferred method for monitoring Human Cytomegalovirus (HCMV) reactivation. However, the relationship between HCMV DNA and antigenemia levels is still under investigation. The aim of this study was to analyse the relationship between HCMV DNA and pp65 antigenemia levels in order to identify clinically useful threshold values for the management of patients. Methods 475 consecutive samples from 156 immunosuppressed patients were tested for HCMV by pp65 antigenemia and Real-time PCR assay. Results 136 out of 475 consecutive samples derived from 48 patients showed evidence of HCMV infection. HCMV DNA was detected in 106 samples, pp65 antigen in 3, and both markers in 27. pp65 antigen detection was associated with higher HCMV DNA levels. The cut-off HCMV DNA level that best predicted pp65 antigenemia in this series of samples was 11,500 copies/ml, but different threshold levels could be observed for specific groups of patients. HCMV disease was observed in 5 out of 48 patients with active HCMV infection. The presence of clinical symptoms was associated with positive pp65 and with higher antigenemia levels. Higher HCMV DNA load at the onset of viral replication was correlated to the development of clinical symptoms. Conclusion Both pp65 antigenemia and HCMV DNA load can be useful for the prospective monitoring of immunocompromised subjects. Specific cut-off levels capable of triggering preemptive antiviral treatment should be determined in accordance to the type of test used and the characteristics of patients and prospectively validated.</p
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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
Appropriate Similarity Measures for Author Cocitation Analysis
No full textWe 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
Defining a new process window for LPBF of Ti-6Al-4V based on micro-warping phenomena
No full textDespite the many advantages that additive technologies have over subtractive ones, low porosity levels, good mechanical properties, and low residual stresses remain the most pressing issues that need further research. In particular, the latter can cause a mismatch between the desired geometry and the geometry that can be achieved.
In this work, a process window for the Laser Powder Bed Fusion (LPBF) process of Ti-6Al-4V alloys, has been identified. The micro-warping phenomenon, which causes the deformation of the printed part during the printing job and the failure of the process, was taken into account together with the parts’ strength, ductility, and porosity. The occurrence of micro-warping phenomena was assessed by the new Warping Alert (WA) parameter,
which depends on the parameters P and v. It was found that, before balling, micro-warping limits the process window in the laser power (P) – laser velocity (v) plane. However, optimal mechanical performances can be found in the proximity of the micro-warping zone, thus making it extremely important to determine the WA threshold value to the process design
Professional football training strategies during home confinement in the COVID-19 pandemic
No full textABS T R A C T BACKGROUND: SARS-CoV-2 emergency forced athletes to train at home on their own and mostly unsupervised, making it difficult to provide training solutions. The aims of the study were 1) to collect data and experiences from a Serie A male football team, a top-level female football team and a male young elite football team; 2) to compare data from lockdown and pre-lockdown period; 3) to report changes in training strate-gies adopted to overcome logistical constraints and 4) to evaluate their congruence to cardio, strength and stretching recommendation mentioned above; 5) to report compliance through player daily feedback.METHODS: Three different professional football teams were enrolled. From March 16, 2020 to April 13, 2020, data for each team were re-corded weekly and compared to a standard training period (October 15th to November 15th, 2019) from the same groups. The rate of perceived exertion (RPE), Visual Analogue Scale (VAS) and Total Quality of Recovery Scale (TQR) values were used to compare the two periods using The Student t-Test and Pearson Test.RESULTS: Each group chose a different training approach. Between the pre-lockdown and the lockdown period, there was no significant differ-ence in the VAS, TQR and RPE indexes. Other else players' compliance differed between the groups during the lockdown period.CONCLUSIONS: Most athletes maintained a high level of training during the COVID-19 forced isolation, thanks to the help of team athletic trainers who provide functional tools and indications customized for each differ. Athletes' feedback and compliance differed according to their gender and age. Monitoring with live video sessions and social group sharing among younger players improved compliance and aggregation
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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