Foams have been generated from blends of polystyrene and poly(methyl methacrylate) under identical conditions of solvent–nonsolvent ratio, impregnation time, and heating period. Scanning electron micrographs of copper-coated fractured surfaces of the samples reveal a distinct transition in their structures from a more or less homogeneous cell-size distribution with prominent grain boundaries to complete lack of foaming and cellularity through random dispersions of spherical poly(methyl methacrylate) inclusions in polystyrene-foam matrix. Dielectric measurements have been made on test specimens at 9.375 GHz X-band microwave frequency by the method of Smith and Hippel modified by Dakin and Works. Percent porosity is the least at 20 wt% of polystyrene while foam density linearly decreases with percent porosity. Dielectric constant is linear in foam density on direct and semilog scales (passing through unity and zero, respectively), in blend composition and also in percent porosity. Dielectric constant increases with increase of foam density or weight percent of polymethyl-methacrylate and decreases with increase of percent porosity. The dielectric constant is, however, nonlinear in volume fraction of polystyrene on both direct and semilog scales, obeying Weiner's inequalities. The logarithmic law of Lichtenecker and Rother with an empirical factor 0.8276 in the index fits the data best. Specific polarization is minimal at 60 wt% of polymethyl methacrylate. The calculated Bottcher-Bruggleman plot based on the interacting spherical particle model is found to be of limited applicability. This is explained on the basis of long-range intra- and intermolecular dipole–dipole interactions. The pattern of the change of dielectric loss tangent (tan δ), lying in the range 0.150–0.045 and attaining a minimum at 20 wt% polystyrene, has similarly been explained in terms of α and β relaxations due to conformational rearrangements and steric hindrances of rotations. The compressive strength measured as a function of composition shows that the reinforcement depends on an optimization between the degree of cellularity and packing. 相似文献
Ambient dielectric measurements as functions of frequency in X-band microwave region have been made on solid samples of polystyrene. Effects of temperature (?120 to +160°C) at three different frequencies have also been studied. The measurement technique applied based on short-circuited waveguide method of Roberts and von Hippel modified by Dakin and Works for low loss and medium loss samples. Two different types of relaxations are identified originating from main chain motion, wagging, and rotational motions of pendent phenyl group. Intrinsic activation energy for polystyrene molecule, dipole moment per repeat unit, and the average apparent energy of a polystyrene molecule associated with its induced transient dipoles have also been calculated and the data so obtained are explained and compared with standard literature. 相似文献
The present study investigates the propagation of Rayleigh-type wave in a transversely isotropic viscoelastic layer in effect of yielding foundation and rigid foundation in two different cases for two considered models. Numerical computation and graphical demonstration have been carried out for the case when layer is comprised of transversely isotropic viscoelastic Mesaverde clay shale material (Model I) and simply isotropic viscoelastic material (Model II). Closed-form expression of phase velocity and damped velocity for both the cases are deduced analytically. Obtained result is found in well agreement to the established standard results existing in the literature. Significant effect of dilatational viscoelasticity, volume viscoelasticity and yielding parameter on phase and damped velocities for both the considered models has been traced out. The comparative study has been performed to unravel the effect of viscoelasticity over elasticity and anisotropy over isotropy in the context of the present problem. Moreover, comparison of phase and damped velocities for the case of layer with stress-free foundation, layer with rigid foundation and layer with yielding foundation serve as a major highlight of the present work. 相似文献
In this paper a new approach for the representation of multi-variant data is introduced. Current approaches consist on either hard-core coding techniques or conceptual / logical models to integrate structured and semi-structured data in customized, application-specific ways. The representation introduced here relies instead on unfolding technique to represent multi-variant data uniformly. This leads to a framework with core functionalities for organizing structured and semi-structured data. The paper presents also an efficient methodology towards retrieval of data from the proposed storage along with comparative performance analysis against existing practices. Accuracy, precision, and recall of the proposed technique are quantitatively evaluated and carefully reported. 相似文献
Denoising of hyperspectral images (HSIs) is an important preprocessing step to enhance the performance of its analysis and interpretation. In reality, a remotely sensed HSI experiences disturbance from different sources and therefore gets affected by multiple noise types. However, most of the existing denoising methods concentrates in removal of a single noise type ignoring their mixed effect. Therefore, a method developed for a particular noise type doesn’t perform satisfactorily for other noise types. To address this limitation, a denoising method is proposed here, that effectively removes multiple frequently encountered noise patterns from HSI including their combinations. The proposed dual branch deep neural network based architecture works on wavelet transformed bands. The first branch of the network uses deep convolutional skip connected layers with residual learning for extracting local and global noise features. The second branch includes layered autoencoder together with subpixel upsampling that performs repeated convolution in each layer to extract prominent noise features from the image. Two hyperspectral datasets are used in the experiment to evaluate the performance of the proposed method for denoising of Gaussian, stripe and mixed noises. Experimental results demonstrate the superior performance of the proposed network compared to other state-of-the-art denoising methods with PSNR 36.74, SSIM 0.97 and overall accuracy 94.03?%.
Thick films of hydroxyapatite (HA) were deposited on silicon single crystal wafers placed in close proximity to a plate of apatite- and wollastonite-containing glass and dipped into a simulated physiological solution at 36°C. Amorphous calcium phosphate phase present in the glass leached into the solution, causing supersaturation of Ca2+ and PO43- ions. Spherical cap-like islands of calcium phosphate nucleated on Si crystals and grew in size with time. The thickness of the film grown on Si (111) in a solution having a composition similar to that of human blood plasma, and maintained at pH of 7.2, reached 7.1 m in 336 h, compared with a thickness of 12.7 m when the ion concentrations of the solution were doubled. HA films grown on Si (111) showed strong (102) texture. In contrast, hardly any HA film could be grown on Si (100). With increasing pH value of the solution the Ca/P ratio of the film increased. At a pH of 7.2 the as-grown and annealed (at 800°C for 3 h in argon) films had Ca/P ratios of 1.10 and 1.72, respectively. The Vickers hardness and the adhesion strength of the film increased upon annealing. Our results suggest that the driving force for formation of apatite films arises from the lowering of free energy of the supersaturated solution by deposition of ions (Ca, P, O, H) in certain crystallographic arrangements on suitable substrates with low interface energies. 相似文献
Polyethylene (PE, 100 parts by weight) was mixed with methyl methacrylate (MMA, up to 5 parts by weight) at 120°C and subsequently exposed to electron radiation of different doses (up to 20 Mrad) to prepare PE/MMA graft copolymers. Successful grafting was verified by IR spectroscopy. Gel formation indicated crosslinking. Grafting increased with increasing MMA concentration and increasing irradiation dose. Crystalline melting temperature and percent crystallinity were lower than those of untreated PE. Tensile strength, elongation at break and dielectric constant of grafted samples were measured and discussed. 相似文献