Experimental Evaluation of Oxide Nanoparticles as Friction and Wear Improvement Additives in Motor Oil

The effect of two nanoparticle oxides on friction and wear was studied under laboratory test conditions using a reciprocating test machine and two test configurations. The addition of these nanoparticles in base stock oil under certain conditions reduced the coefficient of friction and improved wear, but that depended on the test configuration. Examination of the rubbed surfaces showed the pronounced formation of a tribofilm in some cases, while polishing on the surface was also observed in other cases. Contact configuration is important when oxide nanoparticles are being evaluated and the conclusions about their efficacy can be vastly different

Tribological behavior of N-doped ZnO thin films by metal organic chemical vapor deposition under lubricated contacts

Abstract N-doped ZnO thin films were deposited on 304L stainless steel through the pyrolysis of zinc acetate and ammonium acetate in different ratios at a temperature of 420 °C using metal organic chemical vapor deposition. Compositional and structural analyzes of the films were performed by using Rutherford backscattering spectroscopy and X-ray diffraction. The frictional behavior of the thin films and 304L stainless steel substrate was evaluated using a ball-on-flat configuration with reciprocating sliding under marginally lubricated and fully flooded conditions. Al alloy (2017) was used as ball counterface, while basestock synthetic polyalfaolefin oil (PAO10) without additives was used as lubricant. The flat and ball counterface surfaces were examined to assess the wear dimension and failure mechanism. Under marginally lubricated condition, N-doped ZnO thin films provided significant reduction in friction, whereas the films have minimal or no effect in friction under fully flooded condition. N-doped ZnO thin films showed a significant effect in protecting the ball counterface as wear volume was reduced compared with that of the substrate under the marginally lubricated condition. Under the fully flooded condition, with the exception of one of the films, the wear volume of the N-doped ZnO thin films ball reduced compared with that of the substrate. In all the ball counterfaces for N-doped ZnO thin films under both conditions, wear occurred through abrasive mechanism of various degrees or mild polishing. Thus, superfluous lubrication of N-doped ZnO thin films is not necessary to reduce friction and wear

An Experimental and Numerical Analysis of the Compression of Bimetallic Cylinders

This paper investigates the upsetting of bimetallic cylinders with an aluminum alloy center and a brass ring. The influence of the center-ring shape factor and type of assembly fit (interference and clearance), and the effect of friction on the compression force and ductile damage are comprehensively analyzed by means of a combined numerical-experimental approach. Results showed that the higher the shape factor, the lower the forces required, whereas the effect of friction is especially important for cylinders with the lowest shape factors. The type of assembly fit does not influence the compression force. The accumulated ductile damage in the compression of bimetallic cylinders is higher than in single-material cylinders, and the higher the shape factor, the lower the damage for the same amount of stroke. The highest values of damaged were found to occur at the middle plane, and typically in the ring. Results also showed that an interference fit was more favorable for preventing fracture of the ring than a clearance fit. Microstructural analysis by scanning electron microscopy revealed a good agreement with the finite element predicted distribution of ductile damage

Evolving phenotypes of non-hospitalized patients that indicate long COVID

International audienceAbstract Background For some SARS-CoV-2 survivors, recovery from the acute phase of the infection has been grueling with lingering effects. Many of the symptoms characterized as the post-acute sequelae of COVID-19 (PASC) could have multiple causes or are similarly seen in non-COVID patients. Accurate identification of PASC phenotypes will be important to guide future research and help the healthcare system focus its efforts and resources on adequately controlled age- and gender-specific sequelae of a COVID-19 infection. Methods In this retrospective electronic health record (EHR) cohort study, we applied a computational framework for knowledge discovery from clinical data, MLHO, to identify phenotypes that positively associate with a past positive reverse transcription-polymerase chain reaction (RT-PCR) test for COVID-19. We evaluated the post-test phenotypes in two temporal windows at 3–6 and 6–9 months after the test and by age and gender. Data from longitudinal diagnosis records stored in EHRs from Mass General Brigham in the Boston Metropolitan Area was used for the analyses. Statistical analyses were performed on data from March 2020 to June 2021. Study participants included over 96 thousand patients who had tested positive or negative for COVID-19 and were not hospitalized. Results We identified 33 phenotypes among different age/gender cohorts or time windows that were positively associated with past SARS-CoV-2 infection. All identified phenotypes were newly recorded in patients’ medical records 2 months or longer after a COVID-19 RT-PCR test in non-hospitalized patients regardless of the test result. Among these phenotypes, a new diagnosis record for anosmia and dysgeusia (OR 2.60, 95% CI [1.94–3.46]), alopecia (OR 3.09, 95% CI [2.53–3.76]), chest pain (OR 1.27, 95% CI [1.09–1.48]), chronic fatigue syndrome (OR 2.60, 95% CI [1.22–2.10]), shortness of breath (OR 1.41, 95% CI [1.22–1.64]), pneumonia (OR 1.66, 95% CI [1.28–2.16]), and type 2 diabetes mellitus (OR 1.41, 95% CI [1.22–1.64]) is one of the most significant indicators of a past COVID-19 infection. Additionally, more new phenotypes were found with increased confidence among the cohorts who were younger than 65. Conclusions The findings of this study confirm many of the post-COVID-19 symptoms and suggest that a variety of new diagnoses, including new diabetes mellitus and neurological disorder diagnoses, are more common among those with a history of COVID-19 than those without the infection. Additionally, more than 63% of PASC phenotypes were observed in patients under 65 years of age, pointing out the importance of vaccination to minimize the risk of debilitating post-acute sequelae of COVID-19 among younger adults