Process noise covariance estimation via stochastic approximation

Kalman filtering for linear systems is known to provide the minimum variance estimation error, under the assumption that the model dynamics is known. While many system identification tools are available for computing the system matrices from experimental data, estimating the statistics of the output and process noises is still an open problem. Correlation-based approaches are very fast and sufficiently accurate, but there are typically restrictions on the number of noise covariance elements that can be estimated. On the other hand, maximum likelihood methods estimate all elements with high accuracy, but they are computationally expensive, and they require the use of external optimization solvers. In this paper, we propose an alternative solution, tailored for process noise covariance estimation and based on stochastic approximation and gradient-free optimization, that provides a good trade-off in terms of performance and computational load, and is also easy to implement. The effectiveness of the method as compared to the state of the art is shown on a number of recently proposed benchmark examples.     

Transient and steady states of Gd2Zr2O7 and 2ZrO2∙Y2O3 (ss) interactions with calcium magnesium aluminium silicates

Reactions between calcium magnesium aluminium silicates (CMAS) and Gd₂Zr₂O₇ or 2ZrO₂?Y₂O₃ (ss) are investigated within a temperature range of 1200–1300 °C and for durations of 1 h–100 h. The evolution of CMAS penetration depth in Gd₂Zr₂O₇ and 2ZrO₂?Y₂O₃ (ss) pellets varies considerably depending on the interaction time. A quantitative analysis of the nature and composition of phases observed in stationary conditions (powder/powder interaction) is performed by SEM-FEG coupled with WDS analyses using micro-agglomerated nanoparticles of Gd₂Zr₂O₇ and 2ZrO₂?Y₂O₃. Faster kinetics of the gadolinium-based system are illustrated through an analysis of the morphology of the reaction area and of the resulting CMAS tightness of reaction products. The compositions and quantities of reaction products observed at equilibrium are very similar for the two systems, but transient states are significantly different.     

Predicting mode-II delamination suppression in z-pinned laminates

A finite element model for predicting delamination resistance of z-pin reinforced laminates under the mode-II load condition is presented. End notched flexure specimen is simulated using a cohesive zone model. The main difference of this approach to previously published cohesive zone models is that the individual bridging force exerted by z-pin is governed by a specific traction-separation law derived from a unit-cell model of single pin failure process, which is independent of the fracture toughness of the unreinforced laminate. Therefore, two separate traction-separation laws are employed; one represents unreinforced laminate properties and the other for the enhanced delamination toughness owing to the pin bridging action. This approach can account for the so-called large scale bridging effect and avoid using concentrated pin forces in numerical models, thus removing the mesh-size dependency and permitting more accurate and reliable computational solutions.     

A new test cell for the evaluation of thermo-physical performance of facades building components

How do the new building façade components work under real climatic conditions? The question is especially related to the dynamic behaviour of new and complex components such as the ventilated walls, the Phase Change Material, or others that use nano-technologies and aerogels. One of the objectives of the undergoing research activity, named Abitare Mediterraneo, is the evaluation of their thermal behaviour through the use of an outdoor test cell, in order to reproduce under the real external conditions the performance of these components, and consequently define the main thermal parameters such as the attenuation factor and the thermal inertia, characterising the component; moreover, the results will be used to write new algorithms for dynamic simulation tools allowing an appropriate evaluation of the complex behaviour of the whole building at a real scale condition. The new test cell is realised in Florence, Italy. The design starts from the study of the experience of the existing PASSYS test cells, overtaking the main weakness of the building structure and of the heat-flux sensors.     

Glass-Ceramic Materials for Guided-Wave Optics

Glass-ceramics (GCs) are multiphase micro- or nano-crystalline materials produced by the controlled nucleation and crystallization of an amorphous glass through a proper heating or chemical process. Most optical applications require transparency, and this usually implies that the crystalline phase be made of nanocrystals. Transparent GCs are able to combine the advantages of all their components, glasses, and crystals. Incorporation of semiconducting, ferroelectrical, and nonlinear optical phases in glass matrices can produce very promising materials for different applications. A very important role is played by nanocrystals which are activated by luminescent species, as rare earth ions. The presence of the crystalline environment around a rare earth ion allows high absorption and emission across sections, and reduction in the nonradiative relaxations thanks to the lower phonon cut-off energy. Such materials may lead to real advances in optical amplifiers, up-conversion fibers, solid-state lasers, medical sensors, and several other devices, especially if combined with a guided-wave configuration, which allows high energy densities and efficient delivery of the transmitted optical beams. The present review article covers the properties and current state of transparent glass-ceramics for guided-wave devices, including the discussion of the preparation methods and of their spectral and luminescent properties.     

Mechanochemical Processing of Mn and Co Oxides: An Alternative Way to Synthesize Mixed Spinels for Protective Coating

High‐Energy Ball Milling (HEBM) is proposed as a cost effective and environmental friendly technique to produce Co‐ and Mn‐ based oxides suitable for application as protective coating. Mixtures of manganese and cobalt oxides in different molar ratio (Co:Mn = 1:1 and Co:Mn = 2:1) were subjected to mechanochemical treatment up to 100 h and morpho‐structural evolution was evaluated. XRD analysis results show that the HEBM treatment promotes the solid‐state reaction of the starting compounds, with the formation of different crystalline phases when compared to high‐temperature solid‐state synthesis. SEM observations and N₂ adsorption measurements suggest that all processed powders are composed by aggregates of nanometric particles. While long milling time is required to complete the reaction, 10 hours are enough to activate the powders to obtain the desired phases after a mild thermal treatment, as evidenced by in situ thermal XRD analysis. Electrical conductivity measures performed with the Van der Pauw method on sintered pellets evidence a significant difference between the two compositions, related to the dual‐phase nature of Co:Mn = 1:1 material at intermediate temperatures (i.e., T < 700°C), Co:Mn = 2:1 sample showing higher conductivity values in the whole tested range (500°C–800°C).     

Design and Characterization of Myristoylated and Non-Myristoylated Peptides Effective against Candida spp. Clinical Isolates

The increasing resistance of fungi to antibiotics is a severe challenge in public health, and newly effective drugs are required. Promising potential medications are lipopeptides, linear antimicrobial peptides (AMPs) conjugated to a lipid tail, usually at the N-terminus. In this paper, we investigated the in vitro and in vivo antifungal activity of three short myristoylated and non-myristoylated peptides derived from a mutant of the AMP Chionodracine. We determined their interaction with anionic and zwitterionic membrane-mimicking vesicles and their structure during this interaction. We then investigated their cytotoxic and hemolytic activity against mammalian cells. Lipidated peptides showed a broad spectrum of activity against a relevant panel of pathogen fungi belonging to Candida spp., including the multidrug-resistant C. auris. The antifungal activity was also observed vs. biofilms of C. albicans, C. tropicalis, and C. auris. Finally, a pilot efficacy study was conducted on the in vivo model consisting of Galleria mellonella larvae. Treatment with the most-promising myristoylated peptide was effective in counteracting the infection from C. auris and C. albicans and the death of the larvae. Therefore, this myristoylated peptide is a potential candidate to develop antifungal agents against human fungal pathogens.     

3D Bioprinting of Gelatin–Xanthan Gum Composite Hydrogels for Growth of Human Skin Cells

In recent years, bioprinting has attracted much attention as a potential tool for generating complex 3D biological constructs capable of mimicking the native tissue microenvironment and promoting physiologically relevant cell–cell and cell–matrix interactions. The aim of the present study was to develop a crosslinked 3D printable hydrogel based on biocompatible natural polymers, gelatin and xanthan gum at different percentages to be used both as a scaffold for cell growth and as a wound dressing. The CellInk Inkredible 3D printer was used for the 3D printing of hydrogels, and a glutaraldehyde solution was tested for the crosslinking process. We were able to obtain two kinds of printable hydrogels with different porosity, swelling and degradation time. Subsequently, the printed hydrogels were characterized from the point of view of biocompatibility. Our results showed that gelatin/xanthan-gum bioprinted hydrogels were biocompatible materials, as they allowed both human keratinocyte and fibroblast in vitro growth for 14 days. These two bioprintable hydrogels could be also used as a helpful dressing material.     

Active Materials for 3D Printing in Small Animals: Current Modalities and Future Directions for Orthopedic Applications

The successful clinical application of bone tissue engineering requires customized implants based on the receiver’s bone anatomy and defect characteristics. Three-dimensional (3D) printing in small animal orthopedics has recently emerged as a valuable approach in fabricating individualized implants for receiver-specific needs. In veterinary medicine, because of the wide range of dimensions and anatomical variances, receiver-specific diagnosis and therapy are even more critical. The ability to generate 3D anatomical models and customize orthopedic instruments, implants, and scaffolds are advantages of 3D printing in small animal orthopedics. Furthermore, this technology provides veterinary medicine with a powerful tool that improves performance, precision, and cost-effectiveness. Nonetheless, the individualized 3D-printed implants have benefited several complex orthopedic procedures in small animals, including joint replacement surgeries, critical size bone defects, tibial tuberosity advancement, patellar groove replacement, limb-sparing surgeries, and other complex orthopedic procedures. The main purpose of this review is to discuss the application of 3D printing in small animal orthopedics based on already published papers as well as the techniques and materials used to fabricate 3D-printed objects. Finally, the advantages, current limitations, and future directions of 3D printing in small animal orthopedics have been addressed.