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Strain-Mediated Substrate Effect on the Dielectric and Ferroelectric Response of Potassium Sodium Niobate Thin Films
摘要： If piezoelectric thin films sensors based on K0.5Na0.5NbO3 (KNN) are to achieve commercialization, it is critical to optimize the film performance using low-cost scalable processing and substrates. Here, sol–gel derived KNN thin films are deposited using a solution with 5% of potassium excess on Pt/TiO2/SiO2/Si and Pt/SrTiO3 substrates, and rapid thermal annealed at 750 ?C for 5 min. Despite an identical film morphology and thickness of ~335 nm, an in-plane stress/strain state is found to be tensile for KNN films on Pt/TiO2/SiO2/Si, and compressive for those on Pt/SrTiO3 substrates, being related to thermal expansion mismatch between the substrate and the film. Correspondingly, KNN films under in-plane compressive stress possess superior dielectric permittivity and polarization in the parallel-plate-capacitor geometry.
关键词： stress/strain,ferroelectric hysteresis,dielectric properties,KNN thin films,sol–gel,thermal expansion
更新于2025-09-04 15:30:14
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Effet de l’interaction lumiere-salinite sur l’activite du photosysteme ii des feuilles excisees de ma?s
摘要： The decline in growth observed in many plants, subjected to salt stress and exposed to sunlight conditions, is often associated with a decrease in their photosynthetic activity. No clear mechanisms of the inhibited photosynthesis have emerged since photosystem II (PS II) is considered to play a key role in the response of leaf photosynthesis to environmental perturbations. The combination of light and salt stress appears to have synergistic effects on the photochemical activity of PSII driving, and to photoinhibition. The objective of this study was to evaluate the reversible effect of salinity and light interaction on maximal quantum efficiency of photosystem II (Fv/Fm.). In this experiment, detached leaves of two forage maize (Zea mays L.) varieties, Aristo and Arper were placed during 6 hours in solutions of different concentrations of NaCl (0, 100, 200 and 300 mM) and subjected to light (1000 μmol m-2 s-1) or obscurity. Then, their contents of sodium were determined. In order to verify the photo-inhibition reversibility, other leaves which were incubated in a solution of 300 Mm NaCl, during 4 hours were transferred in distilled water and also subjected to light or to obscurity. Results indicate that leaves which had been put to absorb NaCl in obscurity showed no change in maximal efficiency of PSII (Fv/Fm). Nevertheless, light treatment associated with salinity generates a photo-inhibition of PSII manifested by a significant decrease in maximal efficiency of PSII. This photo-inhibition, due to an excessive accumulation of sodium in leaves, is reversible. It is quite sufficient to eliminate only one factor of the association light-salinity for the PSII activity resume.
关键词： Light stress,sodium chloride,Zea mays
更新于2025-09-04 15:30:14
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Extent of embossing-related residual stress on the magnetic properties evaluated using neutron grating interferometry and single sheet test
摘要： Due to the permanently increasing maximum speed of modern electric machines, the mechanical load on the electrical steel rises. The punched flux barriers of reluctance machines play an increasingly key role in the mechanical design. The weakening of the material and the notching effect can cause local failure due to centrifugal force. In this paper, a method is presented which induces residual stresses by embossing electrical steel laminations, which contribute to the guidance of the magnetic flux and cause a negligible mechanical weakening of the sheet. The aim of this paper is to demonstrate the effectiveness of these embossed flux barriers. This is achieved by using neutron grating interferometry, that allows the density of the magnetic domains to be resolved locally. Furthermore the influence of the embossing is mapped globally by single sheet tests. The finite element analysis of the forming process derives the residual stress distribution which is responsible for the measured magnetic behavior. In order to isolate the influence of the residual stress, non-embossed and stress-relief annealed specimens are used as a reference for both measurement methods.
关键词： Electrical steel,Forming,Electric drives,Neutron grating,Production,Single sheet tester,Mechanical stress,Embossing
更新于2025-09-04 15:30:14
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Fracture behaviors of a piezoelectric-piezomagnetic sandwich structure under electromechanical loads: plane problem
摘要： The fracture behaviors of a piezoelectric-piezomagnetic sandwich structure with an eccentric internal crack subjected to two kinds of in-plane electromechanical loads have been studied in this paper. A singular integral equation with Cauchy kernel is obtained by means of Fourier transform and further solved by using Gauss-Chebyshev technique. Then the stress intensity factors are obtained and some numerical results are presented to show the e?ects of the material properties, structure geometries, electromechanical loads and the crack location on the stress intensity factors. The conclusions of the present paper may be useful for the design and fracture prediction of layered piezoelectric-piezomagnetic structures.
关键词： sandwich structure,stress intensity factor,plane strain problem,integral transformation,Piezoelectric-Piezomagnetic composite
更新于2025-09-04 15:30:14
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Anomalous Positive Bias Stress Instability in MoS2 Transistors with High-hydrogen-concentration SiO2 gate dielectrics
摘要： For the first time, the anomalous positive bias stress instability of the back gated monolayer polycrystal molybdenum disulfide with field-effect high-hydrogen-concentration SiO2 gate dielectrics is reported in this letter. It is found the threshold voltage shifts exhibits a pronounced turnaround behavior from a positive shift to a negative shift when enlarging the stress voltage and stress time. We relate this anomalous positive bias instability to two physical processes, charge trapping and hydrogen release and migration.
关键词： MoS2 Transistor,Anomalous Positive Bias Stress Instability
更新于2025-09-04 15:30:14
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Photobiomodulation at Multiple Wavelengths Differentially Modulates Oxidative Stress <i>In Vitro</i> and <i>In Vivo</i>
摘要： Photobiomodulation (PBM) is emerging as an effective strategy for the management of multiple inflammatory conditions, including oral mucositis (OM) in cancer patients who receive chemotherapy or radiotherapy. Still, the poor understanding of the mechanisms by which the light interacts with biological tissues and the heterogeneity of light sources and protocols employed worldwide significantly limits its applicability. Reactive oxygen species (ROS) are massively generated during the early phases of OM and play a major role in the pathogenesis of inflammation in general. Here, we report the results of a clinical and experimental study, aimed at evaluating the effect of laser light at different wavelengths on oxidative stress in vivo in oncologic patients suffering from OM and in vitro in two cell types abundantly present within the inflamed oral mucosa, neutrophil polymorphonuclear (PMN) granulocytes, and keratinocytes. In addition to standard ROS detection methods, we exploited a roGFP2-Orp1 genetically encoded sensor, allowing specific, quantitative, and dynamic imaging of redox events in living cells in response to oxidative stress and PBM. We found that the various wavelengths differentially modulate ROS production. In particular, the 660 nm laser light increases ROS production when applied either before or after an oxidative stimulus. In contrast, the 970 nm laser light exerted a moderate antioxidant activity both in the saliva of OM patients and in both cell types. The most marked reduction in the levels of ROS was detected in cells exposed either to the 800 nm laser light or to the combination of the three wavelengths. Overall, our study demonstrates that PBM exerts different effects on the redox state of both PMNs and keratinocytes depending on the used wavelength and prompts the validation of a multiwavelength protocol in the clinical settings.
关键词： Reactive oxygen species,Laser therapy,Photobiomodulation,Oxidative stress,Oral mucositis
更新于2025-09-04 15:30:14
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Finite Element Simulation of Temperature and Stress Field for Laser Cladded Nickel-Based Amorphous Composite Coatings
摘要： In this paper, a nickel-based amorphous composite coating was obtained on the carbon steel surface by the laser cladding process. The thermal ?eld and stress distribution were simulated by using ANSYS ?nite element software where the moving heat source and powder feeding were modelled by the “Element birth and death” method. The simulation results were veri?ed by comparing the cross-sectional pro?le of fusion lines and X-ray stress measurements, respectively. The results on thermal ?eld showed that the cooling rate of the coating could reach up to 10389.15 K/s and it gradually decreased from the outside surface to the interior, which promoted the formation of amorphous phase. The simulated stress ?eld showed that the coating was in the state of tensile stress after cladding and the longitudinal stress was larger than the transverse stress. The coating was experienced with tensile plastic deformation along the laser scanning direction, which resulted in longitudinal residual stress. A higher stress concentration was occurred between the coating layer and substrate, which increased the susceptibility of crack formation. The test results on transverse residual stress were generally consistent with the simulation. On the contrary, the measured longitudinal stress was nearly close to zero, which was not in agreement with the model due to the formation of cracks.
关键词： stress ?eld,temperature ?eld,laser cladding,amorphous,numerical simulation
更新于2025-09-04 15:30:14
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Refluxed Esterification of Fullerenes Conjugated P25 TiO2 Promotes Free Radical Scavenging Capacity and Facilitates Anti-aging Potentials in Human Cells
摘要： Titanium dioxide nanomaterials have good capability to prevent human cells from damage under UV irradiation. However, some studies indicated that the nanoscale of titanium dioxide could potentially cause harmful effects such as free radicals generation under UV irradiation and thereby accelerate the progress of cell aging. Fullerenes can scavenge large amounts of free radicals due to the fact that fullerenes contain enormous amount of π electrons with low lying lowest unoccupied molecular orbital (LUMO), but its adverse properties, such as the poor solubility in water, restricted the applicability. In this study, we employed water-soluble carboxylic acid fullerenes (C60-COOH and C70-COOH) as the free radical scavenger and modify onto the surface of titanium dioxide by refluxed esterification (P25/C60-COOH or C70-COOH) technique. The conformation and properties of theses nanomaterials were characterized by techniques and equipments such as X-ray diffraction (XRD), energy dispersive spectroscopy analysis (EDS), scanning electron microscopy (SEM), thermal gravimetric analysis (TGA), high-resolution transmission electron microscopy (HRTEM), and Fourier transform infrared spectroscopy (FT-IR). We also introduced methylene blue (MB) and rhodamine B (Rh B) as indicator to evaluate and demonstrate the scavenging capacity of these nanomaterials. Moreover, we examined the biocompatibility and UV protection capacity of our P25/fullerene composites in human 293T cells, and applied luciferase activity assay to investigate the possible underlying cell protection mechanisms exhibited by these nanomaterials. Our data indicate that both P25/C60-COOH and P25/C70-COOH could protect human cells against UV exposure. P25/C70-COOH exhibits great anti-inflammation capacity, while as P25/C60-COOH exhibits great anti-oxidative stress and anti-DNA damage capacity. Our results suggest that most of our P25/fullerenes composite materials have the ability to reduce free radicals and exhibit high biomedical potential in anti-inflammation, anti-oxidant, and anti-aging applications.
关键词： refluxed esterification,anti-oxidative stress,UV protection,TiO2/fullerene composites,anti-inflammation
更新于2025-09-04 15:30:14
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Number series of atoms, interatomic bonds and interface bonds defining zinc-blende nanocrystals as function of size, shape and surface orientation: Analytic tools to interpret solid state spectroscopy data
摘要： Semiconductor nanocrystals (NCs) experience stress and charge transfer by embedding materials or ligands and impurity atoms. In return, the environment of NCs experiences a NC stress response which may lead to matrix deformation and propagated strain. Up to now, there is no universal gauge to evaluate the stress impact on NCs and their response as a function of NC size dNC. I deduce geometrical number series as analytical tools to obtain the number of NC atoms NNC(dNC[i]), bonds between NC atoms Nbnd(dNC[i]) and interface bonds NIF(dNC[i]) for seven high symmetry zinc-blende (zb) NCs with low-index faceting: {001} cubes, {111} octahedra, {110} dodecahedra, {001}-{111} pyramids, {111} tetrahedra, {111}-{001} quatrodecahedra and {001}-{111} quadrodecahedra. The fundamental insights into NC structures revealed here allow for major advancements in data interpretation and understanding of zb- and diamond-lattice based nanomaterials. The analytical number series can serve as a standard procedure for stress evaluation in solid state spectroscopy due to their deterministic nature, easy use and general applicability over a wide range of spectroscopy methods as well as NC sizes, forms and materials.
关键词： solid state spectroscopy,analytical number series,semiconductor nanocrystals,zinc-blende nanocrystals,stress evaluation
更新于2025-09-04 15:30:14
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[IEEE 2018 IEEE 6th Workshop on Wide Bandgap Power Devices and Applications (WiPDA) - Atlanta, GA, USA (2018.10.31-2018.11.2)] 2018 IEEE 6th Workshop on Wide Bandgap Power Devices and Applications (WiPDA) - Thermally Triggered SiC MOSFET Aging Effect on Conducted EMI
摘要： In this paper, thermally triggered SiC MOSFET aging effect on SiC based boost PFC converter’s conducted EMI is investigated. Existing EMI evaluation and suppression studies are mostly based on power devices at healthy state. This study provides a comprehensive EMI evaluation at different state of health of SiC MOSFET used in continuous conduction mode (CCM) Boost PFC converter. For this purpose, SiC MOSFET samples are exposed to accelerated aging and the corresponding device degradations are triggered by thermal stresses. To study device characteristics at different state of health, devices under test (DUT) electrical parameters and switching transients are evaluated over aging to support SiC based AC/DC converter’s conducted EMI discussion. Respectively, device aging effect on differential mode (DM) noise and common mode (CM) noise changes are discussed in detail. An 800W single phase CCM Boost PFC prototype is built to evaluate both DM and CM noise in band B frequency range (150kHz~30MHz) with experimental testing results. According to the study, high frequency noise decrement is observed after SiC MOSFET is thermally aged.
关键词： thermal stress,power factor correction (PFC),Accelerated aging,SiC power MOSFET,EMI/EMC
更新于2025-09-04 15:30:14