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Synthesis and Optical Properties of Dipolar Thiazole Derivatives Incorporating Nitro and Amino Substituents
摘要： We report the synthesis of two dipolar thiazole derivatives functionalized with nitro group as electron acceptor and amino group as electron donor, in order to study their optical properties in the UV-vis range. Their structures were verified by 1H NMR, 13C NMR, HRMS and FT-IR. The resulted thiazole derivatives have good thermal stability with decomposition temperature, Td of 320.20 °C and 284 °C for compounds 1 and 2 respectively. The absorbance bands of compound 2 in the UV-vis range are more red-shifted than that of compound 1 which made compound 2 could have high potential as a great organic NLO material.
关键词： NLO,Push-pull,Thiazole derivative,Thermal stability,Dipolar thiazole
更新于2025-09-23 15:22:29
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Structural Stability of Hafnia-Based Materials at Ultra-High Temperature
摘要： This study assesses the structural stability at ultra-high temperature of the following selected compositions: 6.5 and 14 mol. % of RE2O3 (RE = Dy, Y, Er, Yb, and Lu) doped HfO2. Under thermal cycling and thermal shock, the structural stability was evaluated at 2400°C with water vapor flux using a specific test bench with a 3 kW CO2 laser. The cubic phase stability, which is theoretically important in the broad temperature range from 25 to 2800°C, was determined by a quantitative analysis of the X-ray diffractograms. Fully and partially stabilized HfO2, obtained respectively with 14 mol. % and 6.5 mol. % of dopants, showed different behaviors to thermal damage. Thermal expansion was measured up to 1650°C to anticipate dimensional changes of these stabilized samples and to be able to design an optimized material solution fitting with future combustion chamber requirements. All of these results were then considered in order to exhibit a trend on the thermal stability at 2400°C of the ionic radius of the dopants and their optimal doping rates.
关键词： Phase stability,UHTC,Thermal expansion,Spacecraft propulsion,HfO2
更新于2025-09-23 15:22:29
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Preparation and characterization of UV-curable fluorine-silicon block urethane acrylates for application in release films
摘要： A series of fluorine-silicon block urethane acrylates (PSi-FMPG-IPDI-HEMA) were synthesized from hydroxypropyl-terminated polysiloxane (PSi), newly-prepared fluorodiol (FMPG), isophorone diisocyanate (IPDI) and hydroxyethyl methacrylate (HEMA). Their molecular structures were characterized by Fourier transform infrared and gel permeation chromatography. The compatibility of the oligomers with HFMA was validated using UV–vis transmittance analysis. The thermal stability, water and chemical resistance, contact angles and anti-adhesive performance of the films were measured. It was found all the films had good thermal properties, and excellent water and chemical resistance. The FMPG content affected the surface energy and anti-adhesive performance of the films. The films with more FMPG presented lower surface energy, lower peel strength, and higher residual adhesion. More importantly, the release films designed based on the fluorine-silicon block urethane acrylates had tremendous application potential.
关键词： Anti-adhesive performance,Surface energy,Fluorine-silicon block urethane acrylates,Thermal stability
更新于2025-09-23 15:22:29
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Improved thermal stability of Y3Al5O12:Ce3+ phosphor by SiO2 coating
摘要： In this paper, a heterogeneous precipitation method was adopted to coat a SiO2 layer on the surface of Y3Al5O12:Ce3+ phosphor. The surface morphologies, crystal phases, defect concentrations, luminescent properties and thermal stability of coated phosphors were investigated and compared with those of uncoated phosphor. A compact and homogeneous SiO2 layer on the surface of phosphor was determined by SEM-EDS, TEM, XRD and FT-IR results. Two thermoluminescent peaks were found at 112 oC and 248 oC on the thermoluminescence spectrum. Their intensities decreased slowly with the increasing coating amounts. It indicated that their corresponding defect concentrations were gradually reduced. Improved thermal stability was obtained by SiO2 coating in spite of a slight weakening of the emission intensity. The optimum theoretical coating amount was identified as 4%. Moreover, a structural modification mechanism on improved thermal stability of SiO2 coated Y3Al5O12:Ce3+ was proposed.
关键词： Y3Al5O12:Ce3+ phosphor,thermal stability,coating,structural modification mechanism
更新于2025-09-23 15:22:29
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Experimental and computational studies on induced thermochromic effect and re-entrant smectic phase in linear double hydrogen-bonded binary liquid crystal mixtures
摘要： Design and synthesis of the hydrogen-bonded liquid crystalline (HBLC) mixtures are accomplished from diglycolic acid and 4-n-alkoxybenzoic acid (n = 9–12). Spectroscopic characterization such as UV–Vis, FT-IR, and DSC has supported the presence of molecular geometry of HBLC mixtures. Thermochromic effect is analyzed for the polarizing filter applications. Induced new phases (Smectic X and Smectic Cr) and their transitions are confirmed through DSC along with its corresponding optical textures using polarizing microscope. Furthermore, the induced re-entrant smectic ordering due to the lone pair to π* transition is reported using density functional theory (DFT) studies. Dipole moment studies (DFT) clearly give a strong evidence of the existence of nematic and smectic phases due to the monopole–dipole interaction in the present HBLC mixtures. Band gap of the present HBLCs is 5.175 eV, which is calculated by the HOMO–LUMO analysis and is validated using experimental observations. Liquid crystal parameters such as transition temperature, enthalpy values, stability factor and tilt angles are reported.
关键词： thermal stability,Nematic,DFT,re-entrant,thermochromic
更新于2025-09-23 15:22:29
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Noise-optimized ultrastable low-noise current amplifier
摘要： We have developed a noise-optimized ultrastable low-noise current amplifier (ULCA) aimed at reducing the uncertainty at low currents. It involves a thin-film resistor network with 6.75 GΩ at the high-ohmic path which reduces the noise level to 1.6 fA/√Hz. Noise investigations as well as short-term and long-term stability studies were carried out. The stability of the input current gain was measured using a cryogenic current comparator at ±6.1 nA. Methods for investigating the measurement accuracy at low input currents of about 100 pA at a level of below one part in 10^7 are introduced and experimentally verified. The performance of the noise-optimized ULCA is compared with that of the standard variant introduced in 2014. It is shown that the reduced noise floor is achieved without impairing the stability of the transresistance.
关键词： low-current measurement,cryogenic current comparator,current amplifier,stability,noise optimization
更新于2025-09-23 15:22:29
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Influence of lateral methyl and terminal substituents on the mesophase behaviour of four rings azo-ester liquid crystal compounds
摘要： The effect of introducing a lateral methyl substitution into the previously investigated laterally neat four-ring analogues, 4-substituted phenylazo phenyl 4?-(4?-alkoxyphenylazo) benzoates (Ina–e), on their mesophase behaviour was investigated for the newly prepared five homologous series of 4-substituted phenylazo phenyl 4?-(3?-methyl-4?-alkoxyphenylazo) benzoates (IIna–e). Within each homologous series, the alkoxy group varies between 6, 8, 10, 12, 14, and 16 carbons, while the substituent, X, is a polar group that alternatively changes between the electron-donating (CH3O and CH3) groups, and the electron-withdrawing (Br and NO2) groups, including the unsubstituted homologues (IInc). Their mesophase stabilities were determined by DSC and phases identified by PLM. The results showed that independent of the alkoxy-chain length or the polarity of the substituent X, the nematic phase is predominant with relatively high stability and wide temperature ranges. All compounds show a good thermal stability in the mesophases domain, except the nitro and Br substituted derivatives bearing short alkoxy chain length. Comparison of the mesophase behaviour was also made between the present series and corresponding three-ring laterally CH3-substituted azo/ester analogues. UV-vis absorption spectra revealed that derivatives with electron donating or an electron withdrawing groups exhibited redshifts of the π→π* transition compared with unsubstituded derivative.
关键词： optical properties,polarisability anisotropy,mesophase stability,Four-ring azo/ester/azo derivatives,lateral-methyl substitution
更新于2025-09-23 15:22:29
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Different Influence of Grid Impedance on Low- and High- frequency Stability of PV Generators
摘要： Recently, the stability issues when renewable energy sources are connected to weak grid have obtained great attention. The popular view thinks that the grid impedance is adverse to the system stability. However, in this paper, it is first found that for the photovoltaic (PV) generator, the grid impedance has different influence on the system stability depending on the frequency range when the complete model of the PV generator is taken into consideration. That is, the increase of grid impedance can suppress the low-frequency (<50 Hz) oscillation, while the increase of grid impedance degrades the high-frequency (>300 Hz) stability. Concretely, for the low-frequency range mainly dominated by the power loop and voltage loop of the PV generator, the describing function method is adopted to overcome discontinuity and nonlinearity of the power loop. Then, the low-frequency dynamics like power oscillation can be analyzed accurately. For the high-frequency range mainly dominated by the phase-locked loop and current loop of the PV generator, the impedance analysis method is adopted to reveal the high-frequency instability mechanism. Through these analyses, the different influence of grid impedance on the low- and high- frequency stability of PV generators can be clearly distinguished. All the conclusions are verified through the real-time hardware-in-loop (HIL) tests.
关键词： describing function,impedance analysis,PV generators,weak grid,stability analysis
更新于2025-09-23 15:22:29
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A New, Specular Reflection-Based, Precorneal Tear Film Stability Measurement Technique in a Rabbit Model: Viscoelastic Increases Tear Film Stability
摘要： PURPOSE. To develop a safe, noninvasive, noncontact, continuous in vivo method to measure the dehydration rate of the precorneal tear film and to compare the effectiveness of a viscoelastic agent in maintaining the precorneal tear film to that of a balanced salt solution. METHODS. Software was designed to analyze the corneal reflection produced by the operating microscope’s coaxial illumination. The software characterized the shape of the reflection, which became distorted as the precorneal tear film evaporated; characterization was accomplished by fitting an ellipse to the reflection and measuring its projected surface area. Balanced salt solution Plus (BSS+) and a 2% hydroxypropylmethylcellulose viscoelastic were used as the test agents. The tear film evaporation rate was characterized and compared over a period of 20 minutes in 20 eyes from 10 New Zealand white rabbits. RESULTS. The ellipse axes ratio and surface area were found to decrease initially after each application of either viscoelastic or BSS+ and then to increase linearly as the tear film began to evaporate (P < 0.001) for eyes treated with BSS+ only. Eyes treated with BSS+ required 7.5 ± 2.7 applications to maintain sufficient corneal hydration during the 20-minute test period, whereas eyes treated with viscoelastic required 1.4 ± 0.5 applications. The rates of evaporation differed significantly (P < 0.043) between viscoelastic and BSS+. CONCLUSIONS. The shape and surface area of the corneal reflection are strongly correlated with the state of the tear film. Rabbits’ corneas treated with viscoelastic remained hydrated significantly longer than corneas treated with BSS+.
关键词： evaporation,corneal hydration,precorneal tear film stability,viscoelastic,balanced salt solution
更新于2025-09-23 15:22:29
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P-1.3: The conductivity modulation of amorphous zinc tin oxide thin film by Ar plasma treatment
摘要： We propose a method to form low-resistance amorphous zinc tin oxide thin film (a-ZTO) by Ar plasma. The results show that the Ar plasma treatment can effectively decrease the resistivity of the a-ZTO. The ZTO film treated with Ar plasma at suitable time and moderate operating power, exhibits a low sheet resistance of 2.3 kΩ/□. With the help of PECVD-SiOx coverage layer, the sheet resistance of Ar-plasma treated ZTO is enhanced and increases only one order of magnitude after annealing at 230 ℃. As a result, an optimized Ar plasma treatment for fabrication of low-resistance a-ZTO film is presented.
关键词： amorphous zinc tin oxide,thermal stability,Ar plasma treatment,low-resistance
更新于2025-09-23 15:22:29