541 research outputs found
Sensory redundancy management: The development of a design methodology for determining threshold values through a statistical analysis of sensor output data
Sensor redundancy management (SRM) requires a system which will detect failures and reconstruct avionics accordingly. A probability density function to determine false alarm rates, using an algorithmic approach was generated. Microcomputer software was developed which will print out tables of values for the cummulative probability of being in the domain of failure; system reliability; and false alarm probability, given a signal is in the domain of failure. The microcomputer software was applied to the sensor output data for various AFT1 F-16 flights and sensor parameters. Practical recommendations for further research were made
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
Digital upgrade of a bandsaw machine through an innovative guidance system based on the digital shadow concept
Nowadays, there is an increasing trend towards advanced CNC machine tools having a high level of automation. Nevertheless, manually operated equipment is still playing an important role in many industrial workshops. Operators’ experience is still essential in the perspective of increasing productivity, enhancing product quality, reducing manufacturing costs related to tool wear, waste and maintenance. Thus, even manual operations that are apparently less important in terms of product added value may deserve attention and need to be improved according to the principles of the digital transformation era. This paper introduces a structured approach for design, development and implementation of an operator guidance system for a manual bandsaw machine, based on the digital shadow concept and additional feedback sensors. This provides an actual example of how the digital transformation of a small-scale equipment may improve the manufacturing performance and ergonomics as well
A New Channel for the Detection of Planetary Systems Through Microlensing: II. Repeating Events
In the companion paper we began the task of systematically studying the
detection of planets in wide orbits () via microlensing surveys.
In this paper we continue, focusing on repeating events. We find that, if all
planetary systems are similar to our own Solar System, reasonable extensions of
the present observing strategies would allow us to detect 3-6 repeating events
per year along the direction to the Bulge. Indeed, if planetary systems with
multiple planets are common, then future monitoring programs which lead to the
discovery of thousands of stellar-lens events will likely discover events in
which several different planets within a single system serve as lenses, with
light curves exhibiting multiple repetitions. In this paper we discuss
observing strategies to maximize the discovery of all wide-orbit planet-lens
events. We also compare the likely detection rates of planets in wide orbits to
those of planets located in the zone for resonant lensing. We find that,
depending on the values of the planet masses and stellar radii of the lensed
sources (which determine whether or not finite source size is important), and
also on the sensitivity of the photometry used by observers, the detection of
planets in wide orbits may be the primary route to the discovery of planets via
microlensing. We also discuss how the combination of resonant and wide-orbit
events can help us to learn about the distribution of planetary system
properties (S 6.1). In addition, by determining the fraction of short-duration
events due to planets, we indirectly derive information about the fraction of
all short-duration events that may be due to low-mass MACHOs (S 6.2).Comment: 51 pages, 7 figures. To be published in the Astrophysical Journal, 20
February 1999. This completes the introduction to the discovery of planets in
wide orbits begun in astro-ph/9808075, also to appear in ApJ on 20 February
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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
Le conoscenze in FÃsica 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
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
A New Channel for the Detection of Planetary Systems Through Microlensing: I. Isolated Events Due to Planet Lenses
We propose and evaluate the feasibility of a new strategy to search for
planets via microlensing. This new strategy is designed to detect planets in
"wide" orbits, i.e., with orbital separation, greater than .
Planets in wide orbits may provide the dominant channel for the microlensing
discovery of planets, particularly low-mass (e.g., Earth-mass) planets. This
paper concentrates on events in which a single planet serves as a lens, leading
to an isolated event of short duration. We point out that a distribution of
events due to lensing by stars with wide-orbit planets is necessarily
accompanied by a distribution of shorter- duration events. The fraction of
events in the latter distribution is proportional to the average value of
, where is the ratio between \pl and stellar masses. The position
of the peak or peaks also provides a measure of the mass ratios typical of
planetary systems. We study detection strategies that can optimize our ability
to discover isolated short-duration events due to lensing by planets, and find
that monitoring employing sensitive photometry is particularly useful. If
planetary systems similar to our own are common, even modest changes in
detection strategy should lead to the discovery of a few isolated events of
short duration every year. We therefore also address the issue of the
contamination due to stellar populations of any microlensing signal due to
low-mass MACHOs. We describe how, even for isolated events of short duration,
it will be possible to test the hypothesis that the lens was a planet instead
of a low-mass MACHO, if the central star of the planetary system contributes a
measurable fraction of the baseline flux.Comment: 37 pages, 6 figure. To be published in the Astrophysical Journal.
This is part one of a series of papers on microlensing by planetary systems
containing wide-orbit planets; the series represents a reorganization and
extension of astro-ph/971101
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