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61.
Synthesis and thermal,mechanical and gas permeation properties of aromatic polyimides containing different linkage groups 下载免费PDF全文
Ion Sava Stefan Chisca Aleksandra Wolinska‐Grabczyk Andrzej Jankowski Mitica Sava Eugenia Grabiec Maria Bruma 《Polymer International》2015,64(1):154-164
Two series of aromatic polyimides containing various linkage groups based on 2,7‐bis(4‐aminophenoxy)naphthalene or 3,3′‐dimethyl‐4,4′‐diaminodiphenylmethane and different aromatic dianhydrides, namely 4,4′‐(4,4′‐isopropylidenediphenoxy)bis(phthalic anhydride), 4,4′‐(hexafluoroisopropylidene)bis(phthalic anhydride), 3,3′,4,4′ benzophenonetetracarboxylic dianhydride, 9,9‐bis[4‐(3,4‐dicarboxyphenoxy)phenyl]fluorene dianhydride and 4,4′‐(4,4′‐hexafluoroisopropylidenediphenoxy)bis(phthalic anhydride), were synthesized and compared with regard to their thermal, mechanical and gas permeation properties. All these polymers showed high thermal stability with initial decomposition temperature in the range 475–525 °C and glass transition temperature between 208 and 286 °C. Also, the polymer films presented good mechanical characteristics with tensile strength in the range 60–91 MPa and storage modulus in the range 1700–2375 MPa. The macromolecular chain packing induced by dianhydride and diamine segments was investigated by examining gas permeation through the polymer films. The relationships between chain mobility and interchain distance and the obtained values for gas permeability are discussed. © 2014 Society of Chemical Industry 相似文献
62.
Ioan Alin Bucurica Ion V Popescu Cristiana Radulescu Gheorghe Valerica Cimpoca Ioana-Daniela Dulama Sofia Teodorescu Ion Valentin Gurgu Dorin Dacian Let 《Bulletin of Materials Science》2018,41(3):71
Quartz crystal microbalance (QCM) is known as a very sensitive device used for determination of mass quantity adsorbed on sensor surface. Its detection limits are in the range of ng cm\(^{-2}\). The adsorption mechanism of metallic nanoparticles on QCM sensor was investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). This study aims to highlight the importance of QCM applications in nanoparticles deposition field. The layers formed through adsorption process, induced by the oscillations of the QCM sensor, were investigated by AFM for surface topography and for particle mean size values. The morphology of layers and nanoparticles dimensions were determined by SEM. For a more complex investigation of the nanoparticles adsorption mechanism, the chemical composition of layers was achieved using SEM coupled with energy dispersive X-ray spectrometer (SEM-EDS). This preliminary research involved a new approach in characterization of metallic nanoparticles layers to achieve functional assembled monolayers. 相似文献
63.
Evolving improvised ideation from humour constructs: A new method for collaborative divergence 下载免费PDF全文
Gillian Hatcher William Ion Ross Maclachlan Marion Marlow Barbara Simpson Andrew Wodehouse 《Creativity & Innovation Management》2018,27(1):91-101
This paper reviews and applies key principles from improvised comedy (“improv”) to overcome common barriers in effective group ideation, resulting in the formulation and presentation of a new creative idea generation method. The emergence of an innovative product design can be compared to the telling of a funny joke: both combine seemingly unconnected ideas in a way that is both surprising and satisfying. Our research expands upon this link between humour and creativity, and operationalizes the improv principles best suited to the conceptual design process. A workshop‐based methodology was used to select, develop, and refine the method protocol and facilitation technique. Participant feedback and observations have demonstrated how this approach can expand the solution space to support the generation of bold, innovative ideas. Finally, we present a step‐by‐step guide for the new “design improv” method and discuss its potential value in the generation of creative ideas in a group ideation context. 相似文献
64.
The potential differences in bone repair of calvaria defects treated with a collagen sponge (HELISTAT) or a collagen-hydroxyapatite composite (HEALOS) in young and aged rats were evaluated at 8 weeks after surgery. A histomorphometric analysis of new bone formation and an evaluation of angiogenesis, mast cell, and eosinophil local infiltration were performed. Evaluation showed that HELISTAT induced a similar amount of new bone in both young and aged rats. However this occurred to a lesser degree than in young rats treated with HEALOS. The largest number of blood vessels was present in the defects of aged rats treated with HEALOS, and the number of mast cells was highest in the defects treated with HELISTAT in both young and aged rats. Eosinophils were present to the greatest extent in defects treated with HEALOS in comparison to defects treated with HELISTAT in both young and aged rats. Collagen-hydroxyapatite composite (HEALOS) enhances calvarial bone repair more than collagen sponge alone (HELISTAT) in young rats but not in aged rats at 8 weeks after surgery. HEALOS appears to induce a more intense inflammatory response than HELISTAT especially in aged rats. 相似文献
65.
Despite much progress over the past decade, current single nucleotide polymorphism (SNP) genotyping technologies still offer an insufficient degree of multiplexing when required to handle user selected sets of SNPs. In this paper we propose a new genotyping assay architecture combining multiplexed solution-phase single-base extension (SBE) reactions with sequencing by hybridization (SBH) using universal DNA arrays such as all k-mer arrays. Simulation results on datasets both randomly generated and extracted from the NCBI dbSNP database suggest that the SBE/SBH architecture provides a flexible and cost-effective alternative to genotyping assays currently used in the industry, enabling genotyping of up to hundreds of thousands of SNPs per assay 相似文献
66.
R. Alexandrescu I. Morjan R. Birjega I. Soare I. Voicu F. Dumitrache E. Vasile 《Thin solid films》2007,515(24):8438-8445
Undoped and Fe-doped TiO2 nanopowders with Fe/Ti (atomic ratio) precursor concentration ranging from 7% up to 25% have been prepared by the IR laser pyrolysis technique. A sensitized mixture of TiCl4 and Fe (CO)5 was used as titanium and iron precursor, respectively. Reference undoped titania samples with a major concentration of anatase phase (about 90%) were obtained by the same technique by using very high flows of the oxidizing agent (air). The effects of the iron-dopant concentration on the essential structural properties of the resultant powders such as the phase formation, the crystallinity, the average particle size and distributions were systematically investigated by X-ray diffraction, Raman spectroscopy and transmission electron microscopy. The decrease of the TiO2-anatase crystalline phase, the simultaneous increase of the amorphous phase and the decrease in size of particle mean diameter appear as main effects induced by the Fe-dopant concentration. 相似文献
67.
Aromatic polyimide films are processed from polyamic acid solutions. This process involved the simultaneous loss of solvent and chemical conversion of polyamic acid to polyimide, and implied structural reorganization which led to changed physical properties. Polymer films generated from benzophenonetetracarboxylic dianhydride and 4,4′-diamino-3,3′-dimethyl diphenylmethane have been investigated at different stages of thermal treatment. The surface polarity, which was determined by the presence of polar COOH and CONH groups, changed during polyamic acid thermal treatment. These polar groups were removed step by step by imidization process leading to the modification of the physical properties of the polymer film. 相似文献
68.
In this study, new exact Green’s functions and a new exact Green-type integral formula for a boundary value problem (BVP) in thermoelasticity for some spherical wedges with mixed homogeneous mechanical boundary conditions are derived. The thermoelastic displacements are subjected to a heat source applied in the inner points of the spherical wedges and to a mixed non-homogeneous boundary heat conditions. When the thermoelastic Green’s function is derived, the thermoelastic displacements are generated by an inner unit point heat source, described by Dirac’s δ-function. All results are obtained in elementary functions that are formulated in a special theorem. Exact solutions in elementary functions for two particular BVPs of thermoelasticity for spherical wedges also are included. In these particular BVPs, the thermoelastic displacements are subjected to a constant temperature (in the first particular BVP) or to a constant heat source (in the second particular BVP). In both BVPs, the constant temperature or the constant heat source is given on the segment of the radius of the quarter-space. On the boundary half-planes of the quarter-space zero temperature and zero heat flux are prescribed. 相似文献
69.
Multicompartment hydrodynamic model for slurry bubble columns 总被引:1,自引:0,他引:1
A core-annulus multicompartment two-dimensional two-bubble class model accounting for slurry recirculation and coupled with catalyst transport was developed as a part and parcel of the analysis of the behavior of slurry bubble column reactors at high gas throughputs corresponding to the churn turbulent flow regime. The model analyzed the contributions of bubble-induced turbulence closures, bubble coalescence and breakup phenomena, and catalyst axial distribution as the resultant of sedimentation, advection via liquid-solid slip, per-compartment axial dispersion and core-annulus lateral exchange of catalyst by bubble-induced turbulence. The model was also used to analyze the effects of catalyst loading, gas density and superficial velocity, and column diameter and vessel aspect ratio on the hydrodynamics of slurry bubble column reactors, namely, the per-compartment phase holdups and interstitial velocities, pressure gradient, bubble coalescence and break-up rates, and loci of velocity inversion for the gas and slurry profiles. 相似文献
70.
Khodabakhsh Saeedi Alfin Leo Rama B. Bhat Ion Stiharu 《Journal of Mechanical Science and Technology》2012,26(5):1439-1448
The free vibration of a circular plate with multiple perforations is analyzed by using the Rayleigh-Ritz method. Admissible functions are assumed to be separable functions of radial and tangential coordinates. Trigonometric functions are assumed in the circumferential direction. The radial shape functions are the boundary characteristic orthogonal polynomials generated following the Gram-Schmidt recurrence scheme. The assumed functions are used to estimate the kinetic and the potential energies of the plate depending on the number and the position of the perforations. The eigenvalues, representing the dimensionless natural frequencies, are compared with the results obtained using Bessel functions, where the exact solution is available. Moreover, the eigenvectors, which are the unknown coefficients of the Rayleigh-Ritz method, are used to present the mode shapes of the plate. To validate the analytical results of the plates with multiple perforations, experimental investigations are also performed. Two unique case studies that are not addressed in the existing literature are considered. The results of the Rayleigh-Ritz method are found to be in good agreement with those from the experiments. Although the method presented can be employed in the vibration analysis of plates with different boundary conditions and shapes of the perforations, circular perforations that are free on the edges are studied in this paper. The results are presented in terms of dimensionless frequencies and mode shapes. 相似文献