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61.
Influence of two structural phases of Fe3O4 and γ‐Fe2O3 on the properties of polyimide/iron oxide composites
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Simona‐Luminita Nica Valentin Nica Vasile Cristian Grigoras Cristian‐Dragos Varganici Dumitru Popovici Camelia Hulubei Silvia Ioan 《Polymer International》2015,64(9):1172-1181
Partially aliphatic polyimide/iron oxide composites based on the poly(amic acid) from 5‐(2,5‐dioxotetrahydro‐3‐furyl)‐3‐methyl‐3‐cyclohexene‐1,2‐dicarboxylic acid anhydride and 4,4′‐oxydianiline with iron oxide in different weight percentages were obtained. The structural phases of the transition of magnetite to maghemite occurring in these composites, at different temperatures, are discussed. The physical characteristics, including magnetic, thermal, structural and morphological properties, evaluated using X‐ray diffraction, scanning electron microscopy and thermal analysis, are influenced by the interplay of the filler content and the structural changes of the composite. The X‐ray diffraction patterns of all samples show a cubic structure indexed as magnetite (Fe3O4) or maghemite (γ‐Fe2O3). Quantification of these two phases was evidenced by the Rietveld method. The electrical properties analysed under different humidity conditions evidence the potential applicability of these polyimide/iron oxide materials as humidity sensors. © 2015 Society of Chemical Industry 相似文献
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Cristina Damian Nicolae Hurduc Natalia Hurduc Robert Shanks Irene Yarovsky Dumitru Pavel 《Computational Materials Science》2003,27(4):393-402
The paper presents a study concerning the thermal stability and molecular simulation of some aromatic polyethers, containing a pentamethylenic spacer. The polymers were synthesised using a phase transfer catalysis technique, starting from 1,5-dichoropentane and different bisphenols: 4,4′-dihidroxyazobenzene, 4,4′-dihidroxydiphenyl and bisphenol A. For the investigated polymers the molecular simulation was performed prior the synthesis in order to predict the possibility of liquid crystalline behavior. Molecular simulation was also used as a complementary analysis method for a better understanding of the thermal behavior. Thermogravimetric analysis, in static air atmosphere, with a heating rate of 10 °C/min, was used. Cerius2 and Hyperchem programs were used to perform the molecular simulations. All the polymers present a good thermostability with weight loss being up to 300 °C. The kinetic characteristics suggest a complex degradation mechanism, based on successive reactions. The inter-chain interaction estimated using the polar surface and the chain conformation do not significantly influence the polymer thermostabilities. A comparison between simulated and experimental values of the isotropisation temperature and temperature corresponding to 50% weight loss was performed. 相似文献
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Delia Gligor Liana M. Muresan Anca Dumitru I.C. Popescu 《Journal of Applied Electrochemistry》2007,37(2):261-267
Two new modified carbon paste electrodes (CPEs) based on two different X type zeolites, a natural zeolitic volcanic tuff (NZ)
and a NaX type synthetic zeolite (SZ), modified with methylene green (MG) were developed. Cyclic voltammetry measurements
revealed a reasonably fast electron transfer rate and a good stability for both investigated electrodes. The observed differences
between the electrochemical behavior of MG-NZ-CPEs and MG-SZ-CPEs (the effect of pH on the formal standard potential, the
magnitude of the rate constants for heterogeneous electron transfer and electrode response decay) were explained in terms
of zeolites structure. The modified electrodes showed moderate electrocatalytic effect towards H2O2 reduction and a relatively low limit of detection (0.5 mM for MG-NZ-CPEs). 相似文献
67.
Chao Qian Jiguang Rao Dumitru Mihalache Jingsong He 《Computers & Mathematics with Applications》2018,75(9):3317-3330
The nonlocal Davey–Stewartson (DS) I equation with a parity-time-symmetric potential with respect to the -direction, which is called the -nonlocal DS I equation, is a two-dimensional analogue of the nonlocal nonlinear Schrödinger (NLS) equation. The multi-breather solutions for the -nonlocal DS I equation are derived by using the Hirota bilinear method. Lump-type solutions and hybrid solutions consisting of lumps sitting on periodic line waves are generated by long wave limits of the obtained soliton solutions. Also, various types of analytical solutions for the nonlocal NLS equation with negative nonlinearity, including both the Akhmediev breathers and the Peregrine rogue waves sitting on periodic line waves, can be generated with appropriate constraints on the parameters of the obtained exact solutions of the -nonlocal DS I equation. Particularly, we show that a family of hybrid solitons describing the Peregrine rogue wave that coexists with the Akhmediev breather, both of them sitting on a spatially-periodic background can be thus obtained. 相似文献
68.
Hamid A. Jalab Rabha W. Ibrahim Ali M. Hasan Faten Khalid Karim Ala’a R. Al-Shamasneh Dumitru Baleanu 《计算机、材料和连续体(英文)》2021,68(2):1467-1483
The enhancement of medical images is a challenging research task due to the unforeseeable variation in the quality of the captured images. The captured images may present with low contrast and low visibility, which might influence the accuracy of the diagnosis process. To overcome this problem, this paper presents a new fractional integral entropy (FITE) that estimates the unforeseeable probabilities of image pixels, posing as the main contribution of the paper. The proposed model dynamically enhances the image based on the image contents. The main advantage of FITE lies in its capability to enhance the low contrast intensities through pixels’ probability. Initially, the pixel probability of the fractional power is utilized to extract the illumination value from the pixels of the image. Next, the contrast of the image is then adjusted to enhance the regions with low visibility. Finally, the fractional integral entropy approach is implemented to enhance the low visibility contents from the input image. Tests were conducted on brain MRI, lungs CT, and kidney MRI scans datasets of different image qualities to show that the proposed model is robust and can withstand dramatic variations in quality. The obtained comparative results show that the proposed image enhancement model achieves the best BRISQUE and NIQE scores. Overall, this model improves the details of brain MRI, lungs CT, and kidney MRI scans, and could therefore potentially help the medical staff during the diagnosis process. 相似文献
69.
Aliyu Isa Aliyu Fairouz Tchier Mustafa Inc Abdullahi Yusuf Dumitru Baleanu 《Journal of Modern Optics》2019,66(2):136-142
This work studies the (2 + 1)-dimensional nonlinear Schrödinger equation which arises in optical fibre. Grey and black optical solitons of the model are reported using a suitable complex envelope ansatz solution. The integration lead to some certain conditions which must be satisfied for the solitons to exist. On applying the Chupin Liu's theorem to the grey and black optical solitons, we construct new sets of combined optical soliton solutions of the model. Moreover, classification of conservation laws (Cls) of the model is implemented using the multipliers approach. This is achieved by constructing a set of first-order multipliers of a system of nonlinear partial differential equations acquired by transforming the model into real and imaginary components are derived, which are subsequently used to construct the Cls. 相似文献
70.
Gliga Lavinius Ioan Khemmar Redouane Chafouk Houcine Popescu Dumitru 《Wireless Personal Communications》2022,125(3):2253-2275
Wireless Personal Communications - To satisfy the customer demands, the future wireless communication network can be equipped with high speed connectivity. The 5G technology is going to be a... 相似文献