2,275 research outputs found

    Tribological performance of 3D printed neat and carbon fiber reinforced PEEK composites

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    This work investigates the tribological behavior of neat and carbon fiber-reinforced polyether-ether-ketone (PEEK) materials processed using the fused filament fabrication (FFF) technique. The reciprocating sliding behavior of printed polymers against stainless steel (SS) under dry and water-lubricated conditions was studied. The running-in behavior and evolution of friction were dependent on the material combination and sliding conditions. PEEK reinforced with 10 wt% carbon fibers was optimal considering tribological performance. Neat PEEK exhibited a combination of abrasive and adhesive wear mechanisms, while composites primarily showed fiber-matrix debonding and delamination during sliding. The outcome of this work has significance in improving the processing design of PEEK-based materials in extrusion-based 3D printing for tribological applications

    Long long-COVID and vaccine study, Fars, Iran.

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    ObjectiveThe current study aimed to identify the association between COVID-19 vaccination and prolonged post-COVID symptoms (long-COVID) in adults who reported suffering from this condition.MethodsThis was a retrospective follow-up study of adults with long-COVID syndrome. The data were collected during a phone call to the participants in January-February 2022. We inquired about their current health status and also their vaccination status if they agreed to participate.ResultsIn total, 1236 people were studied; 543 individuals reported suffering from long long- COVID (43.9%). Chi square test showed that 15 out of 51 people (29.4%) with no vaccination and 528 out of 1185 participants (44.6%) who received at least one dose of any vaccine had long long- COVID symptoms (p = 0.032).ConclusionsIn people who have already contracted COVID-19 and now suffer from long-COVID, receiving a COVID vaccination has a significant association with prolonged symptoms of long-COVID for more than one year after the initial infection. However, vaccines reduce the risk of severe COVID-19 (including reinfections) and its catastrophic consequences (e.g., death). Therefore, it is strongly recommended that all people, even those with a history of COVID-19, receive vaccines to protect themselves against this fatal viral infection.</div

    Nonlinear modeling of the vehicle/structure interaction on a skewed highway bridge using an iterative uncoupled approach

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    Vehicle/structure interaction is extremely important in determining the structural performance of highway bridges. However, an accurate prediction of the generated vibrations and forces requires a high-fidelity nonlinear 3D model which is sufficiently representative of the actual vehicle and bridge structure. In spite of all the computational advancements, there are still many technical difficulties to obtain a converging solution from a coupled highly nonlinear and highly damped vehicle/structure models. This paper presents an iterative uncoupled approach to obtain an accurate estimation of the vehicle/structure interaction. The multi-axle vehicle is simulated using a nonlinear 3D multibody dynamics model. The bridge model also contains several nonlinear components to accurately model the bridge behavior. The vehicle/bridge interaction results are obtained through an iterative solution by exchanging the outputs of two uncoupled nonlinear models. A convergence criterion is selected to obtain a reliable solution after several of these iterations. Finally, a reduced-order model of the bridge is developed using a state-space model. The linear reduced-order model of the bridge is coupled with the nonlinear vehicle model to improve the solution time of the analysis. The results are in a very good agreement with the iterative uncoupled approach. © 2012 SPIE.</p

    Inclusivity in global research.

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    ObjectiveThe current study aimed to identify the association between COVID-19 vaccination and prolonged post-COVID symptoms (long-COVID) in adults who reported suffering from this condition.MethodsThis was a retrospective follow-up study of adults with long-COVID syndrome. The data were collected during a phone call to the participants in January-February 2022. We inquired about their current health status and also their vaccination status if they agreed to participate.ResultsIn total, 1236 people were studied; 543 individuals reported suffering from long long- COVID (43.9%). Chi square test showed that 15 out of 51 people (29.4%) with no vaccination and 528 out of 1185 participants (44.6%) who received at least one dose of any vaccine had long long- COVID symptoms (p = 0.032).ConclusionsIn people who have already contracted COVID-19 and now suffer from long-COVID, receiving a COVID vaccination has a significant association with prolonged symptoms of long-COVID for more than one year after the initial infection. However, vaccines reduce the risk of severe COVID-19 (including reinfections) and its catastrophic consequences (e.g., death). Therefore, it is strongly recommended that all people, even those with a history of COVID-19, receive vaccines to protect themselves against this fatal viral infection.</div

    The persistent shadow of the supermassive black hole of M 87

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    In April 2019, the Event Horizon Telescope (EHT) Collaboration reported the first-ever event-horizon-scale images of a black hole, resolving the central compact radio source in the giant elliptical galaxy M 87. These images reveal a ring with a southerly brightness distribution and a diameter of ∼42 μas, consistent with the predicted size and shape of a shadow produced by the gravitationally lensed emission around a supermassive black hole. These results were obtained as part of the April 2017 EHT observation campaign, using a global very long baseline interferometric radio array operating at a wavelength of 1.3 mm. Here, we present results based on the second EHT observing campaign, taking place in April 2018 with an improved array, wider frequency coverage, and increased bandwidth. In particular, the additional baselines provided by the Greenland telescope improved the coverage of the array. Multiyear EHT observations provide independent snapshots of the horizon-scale emission, allowing us to confirm the persistence, size, and shape of the black hole shadow, and constrain the intrinsic structural variability of the accretion flow. We have confirmed the presence of an asymmetric ring structure, brighter in the southwest, with a median diameter of 43.3−3.1+1.5 μas. The diameter of the 2018 ring is remarkably consistent with the diameter obtained from the previous 2017 observations. On the other hand, the position angle of the brightness asymmetry in 2018 is shifted by about 30° relative to 2017. The perennial persistence of the ring and its diameter robustly support the interpretation that the ring is formed by lensed emission surrounding a Kerr black hole with a mass ∼6.5 × 109 M⊙. The significant change in the ring brightness asymmetry implies a spin axis that is more consistent with the position angle of the large-scale jet

    The Event Horizon Telescope Image of the Quasar NRAO 530

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    We report on the observations of the quasar NRAO 530 with the Event Horizon Telescope (EHT) on 2017 April 5−7, when NRAO 530 was used as a calibrator for the EHT observations of Sagittarius A*. At z = 0.902, this is the most distant object imaged by the EHT so far. We reconstruct the first images of the source at 230 GHz, at an unprecedented angular resolution of ∼20 μas, both in total intensity and in linear polarization (LP). We do not detect source variability, allowing us to represent the whole data set with static images. The images reveal a bright feature located on the southern end of the jet, which we associate with the core. The feature is linearly polarized, with a fractional polarization of ∼5%-8%, and it has a substructure consisting of two components. Their observed brightness temperature suggests that the energy density of the jet is dominated by the magnetic field. The jet extends over 60 μas along a position angle ∼ −28°. It includes two features with orthogonal directions of polarization (electric vector position angle), parallel and perpendicular to the jet axis, consistent with a helical structure of the magnetic field in the jet. The outermost feature has a particularly high degree of LP, suggestive of a nearly uniform magnetic field. Future EHT observations will probe the variability of the jet structure on microarcsecond scales, while simultaneous multiwavelength monitoring will provide insight into the high-energy emission origin

    Prevalence of Clinical Symptoms of COVID-19 in Pediatrics: A Systematic Review and Meta-Analysis

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    Background & aim: COVID-19 has numerous and diverse clinical symptoms in different groups, which highlights the identification of common symptoms in children as silent carriers and the timely identification of patients to control the spread of this disease. Therefore, the aim of the present study was to determine and investigate the prevalence of clinical symptoms of COVID-19-19 in children. Methods: The present review and meta-analysis study was conducted according to PRISMA guidelines. The prevalence of symptoms as identification factors of children with COVID-19 at the time of arrival to the hospital between January 2020 and April 2022 was investigated. Articles used in international and domestic databases using the keywords "children", "children", "Covid-19", "symptoms", "clinical symptoms", "fever", "diarrhea", "vomiting" ", "shortness of breath", "cough", "headache", "nausea", "shivering", "body pain", "fatigue" and "malaise" were searched. The collected data were evaluated using the Egger test to check the diffusion error and heterogeneity using the I2 test. Results: In order to determine the prevalence of symptoms of covid-19 in children, a total of 261 articles were received, and finally 21 articles were considered in the analysis. In general, 2200 patients were examined in the present study. According to the results, fever with an overall prevalence of 47% and a confidence interval of 95% (38.96-50.50) is the highest symptom and diarrhea with an overall prevalence of 6.69% and a confidence interval (5.42-8.05) is the lowest. Conclusion: According to the results of the present study, fever and cough were two prominent symptoms of the covid-19 disease in children, and considering that these two symptoms are common symptoms in most children's diseases, during the current epidemic, it is necessary to identify sick children or be considered contaminated

    Using visual and linguistic framing to support sustainable decisions in an online store

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    Companies face several digital communication challenges when it comes to promoting green products or services. The framing effect, which refers to the presentation of information, can significantly influence decision-making in digital interfaces. This research explores the impact of information framing through text and visuals on purchase decisions for sustainable fashion products. An online evaluation study (&#x1d441; = 84) of an e-commerce environment was conducted. We found that visual framing significantly affected user product choices, supporting more sustainability decisions. In contrast, little evidence was found that supported the effectiveness of linguistic (i.e., message) framing on user product choices. We discuss implications on how product pages should be designed to encourage sustainable decision-making
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