Influence of the Experimental Setup on the Damping Properties of SLM Lattice Structures

Background: Metal lattice structures obtained through Selective Laser Melting may increase the strength-to-weight ratio of advanced 3D printed parts, as well as their damping properties. Recent experimental results showed that AlSi10Mg and AISI 316L lattices are characterized by higher Rayleigh damping coefficients with respect to the fully dense material. However, some unclear or contradictory results were found, depending on the experimental setup adopted for modal analysis. Objective: In this work the influence of the experimental setup when performing modal analysis on different SLM AISI 316L lattice structures was deeply investigated. The study provides a critical comparison of various experimental modal analysis approaches, allowing to evaluate the influence of external damping sources and material internal damping phenomena. Methods: The dynamic behaviour of SLM AISI 316L specimens incorporating lattice structures was estimated by means of pulse testing and sinusoidal excitation through an electromagnetic shaker. The validity of the viscous damping model was assessed by means of sinusoidal excitation with different levels of vibration velocity. Moreover, the influence of experimental setup on modal analysis results was critically evaluated, by considering different actuators, contact and non-contact sensors and boundary/clamping conditions. Results: The classical viscous damping model describes with good approximation the damping properties of SLM lattice structures. When exciting single specimens in free-free conditions, those embedding lattice structure and unmelted metal powder filler were characterized by superior internal damping properties with respect to the specimens incorporating the lattice structure without any filler, which was however more effective than the full density equivalent material. Most of the other experimental setups introduced additional external damping sources, that could alter this important outcome. Conclusions: SLM lattice structures embedded into 3D printed components provide superior damping properties against mechanical and acoustic vibrations and the metal powder filler does significantly enhance such damping capacity. A correct estimation of material internal damping was achieved by applying non-contact sensors and free-free boundary conditions, whereas other experimental setups were partly inadequate

Passive chatter suppression of thin-walled parts by means of high-damping lattice structures obtained from selective laser melting

Chatter vibrations arising during machining operations are detrimental for cutting process performance, since they may cause poor surface quality of the machined part and severe damages to machine tool elements. Passive approaches for chatter suppression are based on the integration of special mechanical components with high-damping properties within the machining system. They represent a good solution to this problem thanks to their intrinsic simplicity. Recently, the application of metallic lattice structures inside 3D printed parts obtained from the Selective Laser Melting technology have proven superior damping properties with respect to the same full density material. Here, this idea is further explored by considering the novel configuration where the unmelted powder grains are retained inside the lattice structure by an external shell, acting as a multiplicity of microscopic mechanical dampers. This concept is applied for passive chatter suppression of thin-walled parts that are of particular relevance for industry. Preliminary experimental investigation was first carried out on simple beam-like specimens, and then on thin-walled benchmarks that were identified through modal analysis and tested under real cutting conditions. The main conclusion is that the novel proposed configuration (lattice plus unmelted powder) has higher damping properties with respect to the full density and lattice alternatives. Accordingly, it may be successfully applied for passive chatter suppression in real machining operations

Le conoscenze in Física all'inizio dei corsi universitari in Italia

The article reports the results of an investigation on Italian university students concerning physics knowledge related to common sense schemes at the beginning of the university courses. The results of the diagnosis were communicated both to the students and to the teachers of the courses. The communication enabled the teachers, in the didactical practice, to pinpoint and discuss with the students the discrepancies between the scientific newtonian scheme and common sense scheme. A posttest, given at the end of the course, gives the indication that this practice is effective in inducing a change in the students ideas, notwithstanding the fact that no complete understanding of the scientific viewpoint is teached by the majority of students

Type Ia supernova Hubble diagram with near-infrared and optical observations

We main goal of this paper is to test whether the NIR peak magnitudes of SNe Ia could be accurately estimated with only a single observation obtained close to maximum light, provided the time of B band maximum and the optical stretch parameter are known. We obtained multi-epoch UBVRI and single-epoch J and H photometric observations of 16 SNe Ia in the redshift range z=0.037-0.183, doubling the leverage of the current SN Ia NIR Hubble diagram and the number of SNe beyond redshift 0.04. This sample was analyzed together with 102 NIR and 458 optical light curves (LCs) of normal SNe Ia from the literature. The analysis of 45 well-sampled NIR LCs shows that a single template accurately describes them if its time axis is stretched with the optical stretch parameter. This allows us to estimate the NIR peak magnitudes even with one observation obtained within 10 days from B-band maximum. We find that the NIR Hubble residuals show weak correlation with DM_15 and E(B-V), and for the first time we report a possible dependence on the J_max-H_max color. The intrinsic NIR luminosity scatter of SNe Ia is estimated to be around 0.10 mag, which is smaller than what can be derived for a similarly heterogeneous sample at optical wavelengths. In conclusion, we find that SNe Ia are at least as good standard candles in the NIR as in the optical. We showed that it is feasible to extended the NIR SN Ia Hubble diagram to z=0.2 with very modest sampling of the NIR LCs, if complemented by well-sampled optical LCs. Our results suggest that the most efficient way to extend the NIR Hubble diagram to high redshift would be to obtain a single observation close to the NIR maximum. (abridged)Comment: 39 pages, 15 figures, accepted by A&

The risk of falling

Abstract: In the late 1960s, much interest was raised in regard to biomedical applications of various ceramic materials. A little bit later, such materials were named bioceramics. This review is limited to bioceramics prepared from calcium orthophosphates only, which belong to the categories of bioactive and bioresorbable compounds. There have been a number of important advances in this field during the past 30–40 years. Namely, by structural and compositional control, it became possible to choose whether calcium orthophosphate bioceramics were biologically stable once incorporated within the skeletal structure or whether they were resorbed over time. At the turn of the millennium, a new concept of calcium orthophosphate bioceramics—which is able to promote regeneration of bones—was developed. Presently, calcium orthophosphate bioceramics are available in the form of particulates, blocks, cements, coatings, customized designs for specific applications and as injectable composites in a polymer carrier. Current biomedical applications include artificial replacements for hips, knees, teeth, tendons and ligaments, as well as repair for periodontal disease, maxillofacial reconstruction, augmentation and stabilization of the jawbone, spinal fusion and bone fillers after tumor surgery. Exploratory studies demonstrate potential applications of calcium orthophosphate bioceramics as scaffolds, drug delivery systems, as well as carriers of growth factors, bioactive peptides and/or various types of cells for tissue engineering purposes

Smartphone use and addiction during the coronavirus disease 2019 (COVID-19) pandemic: cohort study on 184 Italian children and adolescents

Background: The lives of many children and adolescents are today increasingly influenced by new technological devices, including smartphones. The coronavirus disease 2019 (COVID-19) pandemic occurred in a time of outstanding scientific progress and global digitalization. Young people had relevant adverse psychological and behavioral effects due to the COVID-19 pandemic, mainly related to infection control measures, which led them to spend more time at home and with major use of technological tools. The goal this study proposes is to evaluate health and social outcomes of smartphone overuse among Italian children and adolescents during the COVID-19 pandemic, analyzing patterns and aims of utilization, as well as the eventual presence and degree of addiction. Methods: This study was based on a self-report and anonymous questionnaire, which was administered to 184 Italian school-age (6–18 years) children and adolescents during the second wave of the COVID-19 pandemic. The test was electronically (email, whatsapp) explained and sent by pediatricians either directly to older children (middle and high school), or indirectly, through the help of teachers, to younger ones (primary school). All participants spontaneously and voluntarily joined the present study. The survey was made by 4 sections, and designed to know and outline modalities (frequency, patterns and aims) of smartphone use, adverse outcomes, and related parental behaviors, also in order to reveal the eventual occurrence and degree of addiction. The same information, related to the pre-epidemic period, was also investigated and analyzed. Results: The data obtained revealed a significantly greater adhesion to the questionnaire by females, likely reflecting higher attention and interest than boys to initiatives relating to health education. Our study showed more frequent smartphone use among Italian children and adolescents during the COVID-19 pandemic, compared to the pre-epidemic period. This may be related to the social distancing measures adopted during the months under investigation. The present survey also outlined the changing patterns and aims in the use of smartphones among young people, which allowed to limit some effects of the crisis. Indeed, they were used for human connection, learning and entertainment, providing psychological and social support. Finally, it was observed a significant increase of overuse and addiction. This led to many clinical (sleep, ocular and musculoskeletal disorders), psychological (distraction, mood modification, loss of interest) and social (superficial approach to learning, isolation) unfavorable outcomes. Conclusions: Pediatricians and health care professionals should be aware of the potential risks related to inappropriate use of smartphones. They should monitor, in cooperation with parents, possible associated adverse effects, in order to early recognize signs and symptoms suggestive, or at high risk, for addiction. They must carry out, as well, the necessary interventions to prevent and/or lower the detrimental impact of smartphone overuse on children and adolescents’ health, oriented to sustain adequate physical and psychological development as well as social relationships

Potential of delphinidin-3-rutinoside extracted from Solanum melongena L. as promoter of osteoblastic MC3T3-E1 function and antagonist of oxidative damage

Purpose: Increasing evidence suggests the potential use of natural antioxidant compounds in the prevention/treatment of osteoporosis. This study was undertaken to investigate the effects of purified delphinidin-3-rutinoside (D3R), isolated from Solanum melongena L., on osteoblast viability and differentiation in basal conditions and its ability to protect MC3T3-E1 cells against oxidative damage induced by tert-butyl hydroperoxide (t-BHP). Methods: MC3T3-E1 osteoblastic cells were treated with D3R (10 1211\u201310 125 M for 24 h), followed by treatment with t-BHP (250 \ub5M for 3 h). To test cell viability, MTT test was performed. Apoptotic cells were stained with Hoechst-33258 dye. Cytoskeleton rearrangement was stained with FICT-labelled phalloidin. Intracellular ROS production was measured using dichlorofluorescein CM-DCFA. The reduced glutathione to oxidized glutathione ratio (GSH/GSSG) contents was measured according to the OPT fluorimetric assay. Results: D3R (10 129 M) significantly increases viability of MC3T3-E1 cells and promotes osteoblast differentiation by increasing the expression of type I collagen, alkaline phosphatase and osteocalcin. Pre-treatment with D3R (10 129 M) significantly prevented t-BHP-induced osteoblastic dysfunction and changes in the cytoskeleton organization by decreasing intracellular ROS and preventing the reduction in GSH/GSSG. D3R did not significantly modify the expression of Osteoprotegerin/RANKL system activated by t-BHP suggesting a lack of effect of D3R on osteoblast/osteoclast crosstalk. D3R protective effects against t-BHP-induced osteoblastic dysfunction were mediated by the PI3K/Akt pathway since they were completely prevented by LY294002, a PI3K/Akt specific inhibitor. Conclusions: These findings indicate that D3R protects MC3T3-E1 cells from oxidative damage and suggest the potential utility of dietary D3R supplement to prevent osteoblast dysfunction in age-related osteoporosis

Bracatinga (Mimosa scabrella), eucalipto (Eucalyptus viminalis) e pinus (Pinus taeda) na recuperação de biodiversidade, a nível microbiológico de solos degradados.

Edição dos Anais do Congresso Florestal de Essências Nativas, 2., 1992, São Paulo. Edição especial

Toxoplasma gondii in raw milk from Sicily

Toxoplasma gondii tachyzoites shed in milk of infected animals are a potential source of human infection often underestimated. Furthermore, limited risk assessment studies have been carried out to evaluate the transmission of toxoplasmosis by milk consumption. In this frame the availability of few and often not validated analytical methods can be a major shortcoming when investigating the extent of milk contamination and the parasite viability. To address the issue, 1381 samples of raw milk from unknown sero-status cows, donkeys, sheep and goats were examined for the detection of T. gondii DNA by a real time PCR method targeting the 529bp repeating element. The protozoan DNA was detected in 67 samples of cow’s milk (4,93% and 35% individual and herd prevalence respectively) and in one sample of donkey milk. Allegedly, on farm cats cohabitation as well as extensive management in the cattle farms that tested positive, can be accounted for environmental loading and transmission of T. gondii oocysts that are the unique sources of infection for milk-producing animals. Food safety-wise, results are noteworthy since recently raw cow’s milk consumption has become increasingly popular with the spread of automatic raw milk vending machines. Albeit heating treatment before consumption is mandatory for consumers, neglect of this requirement cannot be ruled out and could lead the way for foodborne infection. This is particularly true in view of evidences that T. gondii tachyzoites in experimentally spiked cow’s milk samples could be able to survive in gastric fluids for long enough (1 h) before reaching the intestine and infect the host