40 research outputs found
An integrated approach based on acoustic emission and mechanical information to evaluate the delamination fracture toughness at mode I in composite laminate
No full texthis paper addresses a new method based on the combination of mechanical behavior and acoustic emission (AE) information of composite materials during mode I delamination. The method is based on a special purpose function, called sentry function, which is defined as the logarithm of the ratio between mechanical energy and acoustic energy (f=Ln(Es/Ea)). The sentry function is used to study the delamination process and to evaluate the delamination fracture toughness in mode I. The relationship between cumulative fracture toughness energy release rate (GI) and the integral of the sentry function during crack propagation showed a transition point with two sensitive regions below and above it. This behavior can be followed to obtain the critical strain energy release rate value (GIc). Results obtained by means of the sentry function are compared with results obtained by a methodology proposed by other author
Feasibility study of adhesive bonding reinforcement by electrospun nanofibers
No full textAbstractIn previous works, the authors showed that the interleaving of an electrospun nylon nanofibrous mat at the interface between adjacent plies of a composite laminate increases the delamination strength. In particular, the nanomat acts a net-like reinforcing web, enabling a ply-to-ply bridging effect. This reinforcing property of the nanomats can be potentially used in other applications which need to improve the fracture resistance of interfaces, such as adhesive bonding. The present work analyses the feasibility of an electrospun polymeric nanomat as adhesive carrier and reinforcing web in industrial bonding. Thus the adhesive is used to pre-impregnate a nylon nanofibrous mat that is then placed at the interface between two metal pieces and then cured. The aim of the work is first to assess the effectiveness of this procedure, by comparison of the mode-I fracture toughness measured with DCB (Double Cantilever Beam) tests with and without the reinforcement in the adhesive layer. For this purpose, a 2024-T3 aluminum alloy will be bonded using a general purpose, one-part epoxy resin with low viscosity
Aerocapture Guidance: Numerical and Artificial Intelligence Solutions
No full textAerospace EngineeringAstrodynamics and Space Mission
Minimum radiative heat-load aerocapture guidance with attitude-kinematics constraints
No full textTo maximize the payload mass, an aerocapture trajectory should be flown in such a way that both the final ΔV and the total heat load are minimized. At very high velocities, the heating due to radiation of high temperature gases in the shock-layer exceeds the heat due to convection. For some aerocapture missions, such a heat load can be 15 times larger than the heat load due to convection. Thus, convective heat load may in some cases be neglected. It is analytically proven that radiative heat load is minimized by the same trajectory that Minimizes The Final Δ V: a bang-bang trajectory, with full lift-up, full lift-down commands. Next, a novel guidance that plans a bang-bang trajectory with constraints in the attitude kinematics is introduced. This allows for achieving an optimal trajectory with only one parameter to be tuned. For the case studied, values of ΔV as low as 100 m/s can be ensured for entry angles between -6° and -5° and a large spectrum of perturbations; with the same guidance, radiative heat load is reduced by up to 20% with respect to traditional aerocapture-guidance methods. Finally, a lateral guidance that makes use of information on the final inclination of the predicted trajectory is introduced. Such guidance allows for very high accuracy in the inclination requirements with only two reversals, and also requires only a single parameter to be tuned. Depending on the tuning, a maximum inclination error of less than 0.1° can be guaranteed.Astrodynamics & Space Mission
Eight weddings and six funerals: An fMRI study on autobiographical memories
No full text“Autobiographical memory” (AM) refers to remote memories from one's own life. Previous neuroimaging studies have highlighted that voluntary retrieval processes from AM involve different forms of memory and cognitive functions. Thus, a complex and widespread brain functional network has been found to support AM. The present functional magnetic resonance imaging (fMRI) study used a multivariate approach to determine whether neural activity within the AM circuit would recognize memories of real autobiographical events, and to evaluate individual differences in the recruitment of this network. Fourteen right-handed females took part in the study. During scanning, subjects were presented with sentences representing a detail of a highly emotional real event (positive or negative) and were asked to indicate whether the sentence described something that had or had not really happened to them. Group analysis showed a set of cortical areas able to discriminate the truthfulness of the recalled events: medial prefrontal cortex, posterior cingulate/retrosplenial cortex, precuneus, bilateral angular, superior frontal gyri, and early visual cortical areas. Single-subject results showed that the decoding occurred at different time points. No differences were found between recalling a positive or a negative event. Our results show that the entire AM network is engaged in monitoring the veracity of AMs. This process is not affected by the emotional valence of the experience but rather by individual differences in cognitive strategies used to retrieve AMs
Surgical strategy in treatment of metopic synostosis in a single centre experience: technical note and quantitative analysis of the outcomes.
No full textTrigonocephaly is the most common craniosynostosis involving orbits. Although some degree of agreement has been reached regarding surgical timing and indications for treatment, there is no consensus regarding the ideal operative technique to guarantee an optimal morphological outcome. The purpose of this study is to describe both strategies and to compare morphological outcomes by means of morphological surface analysis obtained from three-dimensional (3D) stereophotogrammetry, with two different techniques. We retrospectively investigated 43 patients with metopic synostosis surgically treated between 2004 and 2020. Two different techniques were applied, addressed as technique A and B. Ten patients undergone postoperative 3d stereophotogrammetry were enrolled, and cephalometric measurements were taken and compared to a cohort of unaffected patients matched by age and gender. Comparison of the groups demonstrated a hypercorrection of the metopic angle of the second technique, associated with a slightly lower correction of the interfrontoparietal diameter. The metopic angle showed to be significantly undercorrected with the first method. Alternated barrel staving technique appears to be a quick and satisfactory method in cranial remodelling for metopic synostosis. It guarantees an optimal aesthetic result in the first years after surgery. [Abstract copyright: © 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.
Composite 3D vascularization by using sacrificial electrospun sub-micrometric fibres
No full textThe creation of an extensive vasculature in composite structures is a challenge. The Bond and White groups are pioneers of different methods to achieve composite vascularisation, all of them based on the removal of sacrificial micro-fibres previously embedded in a polymer matrix. We propose the use of electrospinning to produce sacrificial sub-micrometric fibres. Advantages derived by the use of this technique are: (i) the collection of fibres in form of a non-woven mat that can be easily embedded in a polymer matrix; (ii) the intrinsic morphology of the non-woven mat that resembles the blood vascular network of living system; (ii) the control of fibre diameters from hundreds of nanometers to few micrometers; (iii) the control of fibre spatial arrangement. Here we present, as a proof of concept, the use of water soluble poly(ethylene oxide) electrospun fibres that can be easily embedded in a low-temperature thermoset polymer matrix and subsequently removed by simply immersing the composite in water. Fibres with different diameters can be used for generating vessels with different diameters. Moreover, non-woven mats either with a random fibre arrangement or with aligned fibres can be used to generate a biomimetic vasculature and unidirectional vessels, respectively. High-temperature thermoset polymer matrix can be similarly vascularized by a smart choice of electrospun fibre material
Microbiology of cardiac implantable electronic device infections
No full textAimsThe aim of the study was to describe the microbiological findings of cardiac implantable electronic devices (CIEDs) infection in the 2000-2011 period at the Cardiology Unit of New Santa Chiara Hospital in Pisa (Italy). Methods and resultsRemoved CIED leads and pocket material were seeded on solid media and isolates tested for antimicrobial susceptibility with the Kirby Bauer method. Electrodes from 1204 patients were analysed and 854 (70.9) tested positive. In 663 (77.6) cases only one species was isolated, in 175 (20.5) two species, and in 14 (1.8) >2 species. In 116 cases material from the pocket was also cultured. The result was consistent with that from the electrodes in 69 (59) cases. In 359 cases a blood sample was also obtained for culture. The result was consistent with that from the leads in 124 (35) cases. A total of 1068 strains were isolated from electrodes. Gram-positive organisms were most frequently isolated (92.5 of isolates); particularly, coagulase-negative staphylococci (CoNS), mainly Staphylococcus epidermidis, in 69 of cases and Staphylococcus aureus in 13.8, Gram-negative rods in 6.1, yeasts in 1 and molds in 0.4. Overall, Oxacillin resistance was 30, in particular 33 among CoNS and 13 among S. aureus. Oxacillin resistance and quinolones resistance have increased in the period 2006-2011 with respect to the 5 years before. Seventeen percent of Enterobacteriaceae strains had a phenotype compatible with extended spectrum beta-lactamase expression. ConclusionsCulture of the leads offers the possibility of an aetiological diagnosis in the majority of cases. When material from the pocket can be obtained, the microbiological result is often consistent with that from the electrodes, while species isolated from blood cultures are often different and more likely to be the result of contamination. Cardiac implantable electronic device infection is more often monomicrobial, CoNS are most frequently isolated and S. epidermidis is largely the main single agent. Very early infections were associated with S. aureus infection. The pattern of susceptibility to antimicrobials is in general that of community-acquired infections, although oxacillin resistance and quinolones resistance has increased in the last 5 years. © The 2012 Author
Two Stage Optimization for Aerocapture Guidance
No full textThis paper proposes a two-stage optimization approach for aerocapture guidance. In classical entry guidance systems, deterministic optimization is used. Large-scale and short-scale density perturbations may strongly affect the performance of the guidance system, and variations in those are usually not accounted for when computing the command. In this work, perturbations that affect the trajectory at future time-steps are taken into consideration when computing the commanded bank angle. The chosen command is optimal based on a set of possible future perturbations, after the observation of which, a correction can be made. Both two-stage stochastic and two-stage robust optimization are proposed as a solution. In a Monte Carlo analysis consisting of 50 runs, the two-stage robust optimization guidance outperforms an optimal, deterministic, numeric predictor-corrector guidance. Excluding one outlier, also the two-stage stochastic optimization makes the guidance perform better than an optimal deterministic numeric predictor-corrector. With either approach, the computational demands are increased by about thirty times compared to an optimal numeric predictor-corrector. Much of the computation time increase may be reduced by parallelization. On the other hand, the extensive tuning required for the optimal numeric predictor-corrector is not needed for the two-stage optimization guidance, making this approach conceptually more robust. Better modeling of the environment may help further improve the performance. Finally, an approximation to the two-stage robust optimization approach is developed. The guidance has computational requirements only four times larger than those of the optimal numeric predictor-corrector guidance, but can be parallelized into two threads, and, except for two outliers, it offers improved performance.Virtual/online event due to COVID-19Astrodynamics & Space Mission
Evaluation of the first automated thyroglobulin assay
No full textThe aim of this study was to investigate technical and analytical performance of the first automated thyroglobulin (Tg) assay (DPC-Immulite(R); Diagnostic Products Corporation, Los Angeles, USA). In imprecision studies using several human serum pools ranging from 21 to 58 replicates, a coefficient of variation of 9.0 % was obtained at a mean Tg concentration of 0.84 ng/ml and of 6.1 % at a Tg concentration of 62.1 ng/ml. In a method comparison with a non-automated assay (BRAHMS LUMItest Tg(R), BRAHMS, Berlin, Germany) using 383 sera of 303 patients with thyroid carcinoma, regression analysis according to Passing and Bablock yielded in the following equation: Immulite Tg=1.6 x BRAHMS Tg - 0.1 ng/ml (Pearson's r=0.979). Sera obtained from 59 patients with thyroid carcinoma enabled comparative follow-up studies; in all cases qualitative agreement was found with regard to increase or decrease of serum Tg; in eight cases, however, Tg was detected with the Immulite assay but not with the BRAHMS assay. Further follow-up proved the presence of thyroid tissue in these patients. From these and further methodological data (dilution linearity, interference studies, carry-over study, high-dose hook properties, and short report time) it is concluded that the DPC-Immulite Tg assay meets the requirements of routine diagnostic use
