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This study aimed at evaluating the cytotoxicity of experimental fluoride-doped hydroxy-calcium-phosphates and their bioactivity in converting them into hydroxy/fluoro‐apatite. Experimental fluoride-doped hydroxy-calcium-phosphates were formulated by using a 1:1 molar ratio of beta-tricalcium phosphate (α-TCP) and monocalcium phosphate monohydrate (MCPM), doped with calcium hydroxide (10 wt%) and calcium and sodium fluoride salts (1:1 molar ratio) at different concentration of (VSG5F%; VSG10F%; VSG20F%) (Patent: WO2019243592). A fluoride-free (VSG) hydroxy-calcium-phosphate was also formulated and used as a control material. Each powder was immersion in SBF (24 h, 2 and 4 weeks) and submitted to the following analysis to evaluate their bioactivity in inducing apatite-like formation: a) vibrational analysis FTRI-ATR; b) X-ray diffraction; c) TEM-EDX-XRD. Cumulative fluoride release (ppm) was performed for up to 2 months. Each powder was immersed in SBF for 24 h and placed into a hDPSCs (200 mg/mL) medium (ISO/EN 10993-12). Serial dilutions of extracts were prepared (1:1-to-1:200) and their cytotoxicity was analyzed using a MTT [3-(4,5- dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay (initial density of 5 ×103), (incubation 24 h, 48 h, 72 h). Cells on tissue culture plates with a medium were used as a control. The results were statistically analyzed by means of analysis of variance (ANOVA) and Tukey's multiple comparison test (α= 0.05). After 2 weeks of storage in SBF, VSG10F and VSG20F were totally converted into crystals of hydroxy/fluoro-apatite. VSG20F still presented unreacted fluoride after 4 weeks of storage, which was continuously released and accumulated in the media. All the powders showed a significant toxicity at all time points at dilution of 1:1. VSG0F and VSG20F showed a significant toxicity after 24 h (dilutions 1:5), but after 72 h a significant increase in cell proliferation was observed in all the SVGF powders. At 1:10, VSG20F showed the greatest toxicity, while at 1:20, VSG10F and VSG20F showed a reduction of cell viability of only 3% and 13% respectively (48 h). At lower dilutions (1:20, 1:100 and 1:200) no powders showed significant toxicity compared to the control, but an increase in cell proliferation was observed at 72 h with VSG5F and VSG10F. The experimental fluoride-doped hydroxy-calcium-phosphates tested in this study may be potentially used for the remineralization of dentine and enamel thanks to their ability to convert into hydroxy/fluoro‐apatite crystals. As a result of their remarkable biocompatibility and to their ability to induce cell proliferation in some specific conditions, the experimental fluoride-doped hydroxy-calcium-phosphates tested in this study could also be employed for the formulation of pulp-protection materials. [ABSTRACT FROM AUTHOR]

Manufacturers of photovoltaic cells and modules usually provide temperature coefficients referring to the short–circuit current, the open–circuit voltage and the maximum power. Few studies analyse the variation of the series resistance with respect to the cell or module temperature. In this paper, this dependency is studied by suitably processing a set of current–voltage curves acquired on several modules working under outdoor conditions. The curves are measured at an increasing module temperature. The temperature coefficient of the series resistance is estimated by using the single diode model and the double diode one. Some hundreds of current vs voltage curves referring to degraded photovoltaic modules are used in this paper to analyse the effects of the degradation on the series resistance and on the temperature coefficient thereof. • A method is proposed to estimate the temperature coefficient of the series resistance. • This is applied to degraded mono-crystalline PV modules under outdoor conditions. • The suitability for determining the series resistance of the DDM vs SDM is confirmed. • The estimations are achieved with high values of the coefficient of determination. • The effect of the degradation mechanisms on the series resistance is also addressed. [ABSTRACT FROM AUTHOR]

This work presents the principle of operation of RotWWC-VSA, a Variable Stiffness Actuator (VSA) characterized by no rotational stroke limits, conversely to the vast majority of rotational VSAs, typically characterized by restrictions in the angular range of motion. The possibility to perform an unlimited number of turns is a characteristic taken for granted for standard motors, but it is not for VSA rotational motors. It features two antagonist nonlinear equivalent springs, each of them made up of a tension spring, a cam and a wire which, properly configured, realize a torsion spring characterized by a customizable non-linear stiffness characteristic. Theoretical aspects of the actuator are accompanied by numerical simulations. Design guidelines are drawn and a concept design is presented. [ABSTRACT FROM AUTHOR]

This work presents the principle of operation of LinWWC-VSA, a Variable Stiffness Actuator (VSA) suitable to perform linear motions, conversely to the vast majority of VSAs typically designed to perform rotational movements and often affected by limits in the actually exploitable range of motions. It features two antagonist nonlinear equivalent springs, each of them made up of a cam wrapped by a wire and constrained by a torsion spring. This work presents methods both for the analysis and the synthesis of the actuator. Two synthesis methods, one numerical and one analytic, are described to design the cam profile as function of the desired stiffness-displacement characteristic of each equivalent nonlinear spring. The analytic method exploits the peculiar formulation of the logarithmic spiral. The theoretical aspects of the actuator are accompanied by numerical simulations. [ABSTRACT FROM AUTHOR]

to compare conventional nanohybrid (Ceram.x Spectra) and ormocer-based (Admira fusion) dental composite resins effects on human dental pulp stem cells (hDPSCs) in terms of cytotoxicity, self-renewal, migration and osteogenic differentiation. hDPSCs were cultured in presence of different dilutions (undiluted, form 1:2 to 1:100) of CeramX (CX) and Admira fusion (AD) eluates and viability assay in standard or osteogenic conditions were performed. Samples and eluates were prepared according to ISO 10993–12. In addition, apoptosis, self-renewal and migration activity evaluations were carried out. Osteogenic differentiation potential was tested by Alkaline Phosphatase Activity, alizarin red staining and gene expression of specific markers (ALP, RUNX2, OCN, OPN and COL1α1). Statistical analysis was performed by means of a One-way analysis of variance (One-way ANOVA) followed by a Tukey's test for multiple comparison; results were presented as mean ± standard error of mean (SEM). Admira Fusion demonstrated to be highly biocompatible and showed positive effects on hDPSCs proliferation and differentiation; on the contrary, conventional nanohybrid composite showed to be more cytotoxic and without any notable effect on stem cells differentiation. Moreover, the obtained results were further corroborated by a significant upregulation of osteogenic differentiation markers obtained in presence of ormocer-based composite resin eluate. Specifically, in AD 1:50 group expression levels of ALP, Runx2, Col1α1 were double than control (ALP, p = 0.045; Runx2, p = 0.003; Col1α1, p = 0.001) and CX 1:50 (ALP, p = 0.006; RUNX2, p = 0.029; Col1α1, p = 0.005). Moreover, in the same group, OPN and OCN resulted about 5 times more expressed as compared to control (OPN, p = 0.009; OCN, p = 0.0005) and CX 1:50 (OPN, p = 0.012; OCN, p = 0.0006). The less cytotoxicity obtained by AD than conventional nanohybrid composite may be attributed to a reduced monomers release in the oral environment, supporting the hypothesis of limited adverse effect and enhanced healing potential, mainly when the material is positioned in close contact with pulp tissue. • Ormocer-based resin demonstrated to be highly biocompatible. • Ormocer-based resin showed positive effects on hDPSCs differentiation. • Ormocer-based resin seemed to be effective in deep cavities approximating pulp. • Ormocer-based resin might enhance pulp tissue healing. [ABSTRACT FROM AUTHOR]

Highlights: [•] The approach allows to simulate cell-by-cell the mismatched PV arrays. [•] The PV array non-linear model is solved by a low computational burden algorithm. [•] The technique is useful to analyze the hot-spot heating and the effect of parametric tolerances. [•] The proposed method is simple to be implemented in any programming language. [ABSTRACT FROM AUTHOR]

Abstract: In this paper a computationally efficient approach to the modeling of a photovoltaic array is presented. It is especially suited for simulating mismatched operating conditions, in which the different modules of the array work at different irradiation levels and temperatures. The model used allows to keep into account parametric tolerances and drifts among the modules. The proposed technique is based on the use of the Lambert W-function, which allows to obtain an explicit relationship between the voltage and the current of any photovoltaic module. The non linear system of equations describing the photovoltaic array is easily solved thanks to the explicit symbolic calculation of the inverse of the Jacobian matrix. The performances of the proposed numerical approach are discussed especially in cases where a deep mismatch affects the photovoltaic array. [Copyright &y& Elsevier]

The power vs. voltage curve of a photovoltaic string operating under mismatched conditions can exhibit more than one maximum power point (MPP). In this paper, a direct method for the estimation of these points using explicit equations is introduced. The method employs a piecewise linear approximation of the current vs. voltage curve of each photovoltaic panel in the string and assumes that the open circuit voltage and the position of the maximum power points of each panel are known. Numerical results comparing the performances of the proposed approach with those offered by the adoption of the accurate single diode model show that the computational burden is reduced by almost four orders of magnitude. The approach is validated by experimental results exhibiting estimation errors lower than 5%. The satisfactory trade-off between accuracy and computation time provided by the proposed method is illustrated using two application examples: reconfiguration and long-term power production of PV strings. Moreover, an in-depth comparison of the existing simplified methods to estimate the MPPs has been performed. [ABSTRACT FROM AUTHOR]

Abstract: The model of photovoltaic (PV) fields in mismatching conditions presented in this paper is a tradeoff between accuracy and calculation time. The detailed single diode model, including series and parallel resistances, is considered for the PV modules, while the bypass and blocking diodes are represented with a piecewise linear model. The model profits from the possibility to express each PV module voltage as an explicit function of the current by using the Lambert-W function. The balancing of the string voltage with those ones of the active and inactive modules, as well as of the blocking diode, allows to construct only one non-linear equation depending on the string current. Consequently, the solution of only one equation allows to calculate the string current for a given string voltage, and the current of the whole field is calculated by adding the currents of all parallel strings. The advantages of the proposed model are illustrated by comparing it with two approaches recently published in literature. The model accuracy is evaluated with small, medium and large PV fields, and its usefulness for performing energetic analysis and dynamical simulations is also illustrated. Finally, experimental validation of the model on a small scale PV array is provided. [Copyright &y& Elsevier]

Abstract: Objectives: Dental resin monomers like triethylene glycol dimethacrylate (TEGDMA) and 2-hydroxyethyl methacrylate (HEMA) are able to cause an imbalance of the redox state in mammalian cells. The resulting oxidative stress originating from reactive oxygen species (ROS) has been associated with cytotoxicity. We hypothesized that ROS might contribute to the generation of genotoxicity by TEGDMA and HEMA as well. Therefore, we examined the formation of micronuclei in V79 cells by both resin monomers in the presence of the antioxidant N-acetylcysteine (NAC), which scavenges ROS. In addition, we analyzed the effects of TEGDMA and HEMA on the normal cell cycle in the presence of NAC. Methods: V79 fibroblasts were exposed to increasing concentrations of TEGDMA and HEMA in the presence and absence of NAC for 24h. Genotoxicity was indicated by the formation of micronuclei. The modification of the normal cell cycle was analyzed by flow cytometry (FACS). Results: A dose-related increase in the number of micronuclei in V79 cells-induced by TEGDMA and HEMA indicated genotoxicity of both chemicals. However, the formation of micronuclei was reduced in the presence of 10mmol/L NAC, indicating its protective role. A cell cycle delay in G2 phase caused by TEGDMA was absent when cells were co-treated with NAC. Similarly, the presence of NAC led to a reversion of the cell cycle delay in HEMA-treated cell cultures. Significance: Our results suggest that genotoxic effects and the modification of the cell cycle caused by TEGDMA and HEMA are mediated, at least in part, by oxidative stress. [Copyright &y& Elsevier]