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  • 1
    Online Resource
    Online Resource
    Effects of Laser Irradiation at 488, 514, 532, 552, 660, and 785 nm on the Aqueous Extracts of Plantago lanceolata L.: A Comparison on Chemical Content, Antioxidant Activity and Caco-2 Viability
    MDPI AG ; 2022
    In:  Applied Sciences Vol. 12, No. 11 ( 2022-05-29), p. 5517-
    Details
    In: Applied Sciences, MDPI AG, Vol. 12, No. 11 ( 2022-05-29), p. 5517-
    Abstract: In this study, six laser radiation (488 nm/40 mW, 514 nm/15 mW, 532 nm/20 mW, 552 nm/15 mW, 660 nm/75 mW, and at 785 nm/70 mW) were tested on the aqueous extracts of leaves of Plantago lanceolata L. to compare extraction efficacy and antioxidant and cell viability effects in vitro. Briefly, in comparison with the control extract, laser extracts at 488, 514, 532, and 552 nm revealed small acquisitions of total extractible compounds in samples (up to 6.52%; laser extracts at 488 and 532 nm also revealed minerals and micro-elements increases (up to 6.49%); the most prominent results were obtained upon Fe (up to 38%, 488 nm), Cr (up to 307%, 660 nm), and Zn (up to 465%, 532 nm). Laser extracts at 488, 514, 552, and 785 nm proved more intense antioxidant capacity than the control sample, while laser extract at 660 nm indicated clear pro-oxidant effects. Caco-2 cells study indicated stimulatory activity for the extracts at 488 nm, no effects at 532 nm, and the decrease of the cell viability in the case of extracts at 660 nm respectively. Further studies are necessary to understand the pro-oxidant effects observed in the case of extracts exposed to laser radiation at 660 nm.
    Type of Medium: Online Resource
    ISSN: 2076-3417
    URL: Article
    DOI: 10.3390/app12115517
    Language: English
    Publisher: MDPI AG
    Publication Date: 2022
    detail.hit.zdb_id: 2704225-X
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  • 2
    Online Resource
    Online Resource
    Subthreshold Laser Ablation Measurements by Langmuir Probe Method for ns Irradiation of HfO2 and ZrO2
    MDPI AG ; 2023
    In:  Materials Vol. 16, No. 2 ( 2023-01-05), p. 536-
    Details
    In: Materials, MDPI AG, Vol. 16, No. 2 ( 2023-01-05), p. 536-
    Abstract: The unbiased Langmuir probe (LP) method was used to perform measurements on HfO2 and ZrO2 samples around the laser ablation threshold on a wide range of irradiation conditions. Important changes in the lifetime (from ms to μs) and the shape of the charge particle current were seen with the increase of the laser fluence. The ablation threshold was estimated by evaluating the overall average ablated charge as a function of the laser fluence. Above the ablation threshold, the generation of high kinetic species is seen, which can reach several keV. An important jump in ion acceleration potential is observed for values above 1 J/cm2, which coincides with the dominant presence of negative ions in the plasma. The evolution of several plasma parameters (ion density, expansion velocity, electron temperature, Debye length) was investigated and correlated with the fundamental ablation mechanism involved in various irradiation regimes. The LP data were correlated with COMSOL simulations on the maximum surface temperature reached during irradiation. Important correlations between the evaporation and melting processes and ablation threshold fluence and ion acceleration phenomena are also reported.
    Type of Medium: Online Resource
    ISSN: 1996-1944
    URL: Article
    DOI: 10.3390/ma16020536
    Language: English
    Publisher: MDPI AG
    Publication Date: 2023
    detail.hit.zdb_id: 2487261-1
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  • 3
    Online Resource
    Online Resource
    On the Regularization of Recursive Least-Squares Adaptive Algorithms Using Line Search Methods
    MDPI AG ; 2024
    In:  Electronics Vol. 13, No. 8 ( 2024-04-13), p. 1479-
    Details
    In: Electronics, MDPI AG, Vol. 13, No. 8 ( 2024-04-13), p. 1479-
    Abstract: Stereophonic acoustic echo cancellation (SAEC) requires the identification of four unknown impulse responses corresponding to four loudspeaker-to-microphone pairs. Recent developments in the field of adaptive filters for SAEC setups have allowed for the handling of a single complex-valued adaptive impulse response, instead of the four classical real-valued adaptive filters. With the simplified framework provided by the widely linear (WL) model, more advanced versions of recursive least-squares (RLS) were employed in order to take advantage of their superior tracking speeds when working with highly correlated input signals (such as speech). Despite the performances and numerical stability provided by using exponentially weighted versions of the RLS family in combination with line search methods (LSMs), the SAEC configurations have limited capabilities in mitigating the negative effects caused by high-level disturbances affecting the two microphone signals. Such is the case of double-talk scenarios, which considerably reduce the update accuracy of the adaptive system. This paper analyzes a regularization technique for the named WL-RLS-LSM adaptive filters by adjusting the correlation matrix associated with the input signals and creating a reaction in the update process. The proposed method is designed to considerably slow (or even freeze) the adaptation process while the disturbance is manifested. Simulation results are discussed in order to validate the theoretical content.
    Type of Medium: Online Resource
    ISSN: 2079-9292
    URL: Article
    DOI: 10.3390/electronics13081479
    Language: English
    Publisher: MDPI AG
    Publication Date: 2024
    detail.hit.zdb_id: 2662127-7
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  • 4
    Online Resource
    Online Resource
    Tunable Properties via Composition Modulations of Poly(vinyl alcohol)/Xanthan Gum/Oxalic Acid Hydrogels
    MDPI AG ; 2022
    In:  Materials Vol. 15, No. 7 ( 2022-04-04), p. 2657-
    Details
    In: Materials, MDPI AG, Vol. 15, No. 7 ( 2022-04-04), p. 2657-
    Abstract: The design of hydrogel networks with tuned properties is essential for new innovative biomedical materials. Herein, poly(vinyl alcohol) and xanthan gum were used to develop hydrogels by the freeze/thaw cycles method in the presence of oxalic acid as a crosslinker. The structure and morphology of the obtained hydrogels were investigated by means of scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, and swelling behavior. The SEM analysis revealed that the surface morphology was mostly affected by the blending ratio between the two components, namely, poly(vinyl alcohol) and xanthan gum. From the swelling study, it was observed that the presence of oxalic acid influenced the hydrophilicity of blends. The hydrogels based on poly(vinyl alcohol) without xanthan gum led to structures with a smaller pore diameter, a lower swelling degree in pH 7.4 buffer solution, and a higher elastic modulus. The antimicrobial activity of the prepared hydrogels was tested and the results showed that the hydrogels conferred antibacterial activity against Gram positive bacteria (Staphylococcus aureus 25923 ATCC) and Gram negative bacteria (Escherichia coli 25922 ATCC).
    Type of Medium: Online Resource
    ISSN: 1996-1944
    URL: Article
    DOI: 10.3390/ma15072657
    Language: English
    Publisher: MDPI AG
    Publication Date: 2022
    detail.hit.zdb_id: 2487261-1
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  • 5
    Online Resource
    Online Resource
    CoxCrFeNiTi High-Entropy Alloys Prepared via Mechanical Alloying and Spark Plasma Sintering for Magnetron Sputtering Coatings
    MDPI AG ; 2023
    In:  Materials Vol. 16, No. 19 ( 2023-09-24), p. 6386-
    Details
    In: Materials, MDPI AG, Vol. 16, No. 19 ( 2023-09-24), p. 6386-
    Abstract: The main objective of this study was to develop a high-entropy alloy (HEA) derived from the CoxCrFeNiTi HEA system (x = 0.5, 1) for protective coatings using the magnetron sputtering method. In order to produce the high-entropy alloy targets required for the magnetron sputtering process, mechanically alloyed metallic powders were consolidated via spark plasma sintering (SPS). The microstructural analysis results of the HEA mixture presented morphology changes after 30 h of alloying, with the particles presenting uniform polygonal shapes and dimensions. Subsequently, 316L stainless steel (SS) specimens were coated via magnetron sputtering, comparing their composition with that of the sputtering targets used for deposition to establish stoichiometry. Microstructural analyses of the SPSed HEAs revealed no defects and indicated a uniform elemental distribution across the surface. Furthermore, the CoCrFeNiTi equiatomic alloy exhibited a nearly stoichiometric composition, both in the coating and the sputtering target. The XRD analysis results indicated that amorphous coatings were obtained for both Co0.5CrFeNiTi and the CoCrFeNiTi HEA, and nanoindentation tests indicated that the CoCrFeNiTi HEA coating presented a hardness of 596 ± 22 HV, compared to the 570 ± 19 HV measured for Co0.5CrFeNiTi, suggesting an improved wear resistance.
    Type of Medium: Online Resource
    ISSN: 1996-1944
    URL: Article
    DOI: 10.3390/ma16196386
    Language: English
    Publisher: MDPI AG
    Publication Date: 2023
    detail.hit.zdb_id: 2487261-1
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