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  • Articles  (3,807)
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  • 1
    Publication Date: 2018-03-14
    Description: The structural, optical, and thermal properties of PVC/SnO 2 nanocomposites were investigated. XRD patterns were used to explore the structures of these prepared samples. Optical UV–Vis measurements were analyzed to calculate the spectroscopic optical constants of the prepared PVC/SnO 2 nanocomposites. Both direct and indirect optical band gaps decreased with increasing SnO 2 content. The refractive index, high frequency dielectric constant, plasma frequency, and optical conductivity values increased with SnO 2 . The single oscillator energy increased from 5.64 to 10.97 eV and the dispersion energy increased from 6.35 to 19.80 eV with the addition of SnO 2 . The other optical parameters such as optical moments, single oscillator strength, volume energy loss, and surface energy loss were calculated for different SnO 2 concentrations. Raman spectra of the PVC/SnO 2 nanocomposite films revealed the characteristic vibrational modes of PVC and surface phonon modes of SnO 2 . The thermal stability of PVC/SnO 2 nanocomposite films was studied using DTA and thermogravimetric analysis. The glass transition ( T g ) values abruptly changed from 46 °C for PVC to an average value of 59 °C for the polymer films doped with 2.0, 4.0, and 6.0 wt% SnO 2 . The weight loss decreased as the SnO 2 concentration increased in the temperature range of 350–500 °C, corresponding to enhanced thermal stability.
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    Electronic ISSN: 1432-0630
    Topics: Technology , Physics
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  • 2
    Publication Date: 2018-03-14
    Description: A cloak based on gradient index metamaterial (GIM) is proposed. Here, the GIM is used, for conversion of propagating waves into surface waves and vice versa, to get the cloaking effect. The cloak is made of metamaterial consisting of four supercells with each supercell possessing the linear spatial variation of permittivity and permeability. The spatial variation of material parameters in supercells allows the conversion of propagating waves into surface waves and vice versa, hence results in reduction of electromagnetic signature of the object. To facilitate the practical implementation of the cloak, continuous spatial variation of permittivity and/or permeability, in each supercell, is discretized into seven segments and it is shown that there is not much deviation in cloaking performance of discretized cloak as compared to its continuous counterpart. The crucial advantage, of the proposed cloaks, is that the material parameters are isotropic and in physically realizable range. Furthermore, the proposed cloaks have been shown to possess bandwidth of the order of 190% which is a significantly improved performance compared to the recently published literature.
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  • 3
    Publication Date: 2018-03-14
    Description: We have demonstrated for the first time the permanent local modification of the bulk of silicon by repeated illumination with infrared (1.55 μm) picosecond pulses. Furthermore, we evaluated the characteristics of inscribing permanent modifications in the bulk material for different pulse durations from 0.8 to 10 ps in terms of their reproducibility and controllability of their morphology. Our results are based on a simple experimental setup that demonstrates the possibility of using picosecond pulses for the local modification of bulk silicon as a potential alternative to more complex irradiation strategies required for femtosecond pulse processing.
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  • 4
    Publication Date: 2018-03-14
    Description: In this study, undoped ZnO and yttrium (Y)-doped ZnO (YZO) nanoparticles having different Y dopant concentrations (Zn 1− x Y x O; x  = 0.005, 0.01, 0.015, 0.02) were successfully synthesized by sol–gel dip-coating method. Structural characterizations of the obtained samples were examined with scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) analyses. SEM analysis shows that the synthesized nanoparticles are mostly dot-like structures. The sizes of nanostructures decrease with increasing Y-doping concentration up to 2 mol % Y and XRD results show that all of samples have wurtzite hexagonal structure of ZnO with (002) c-plane orientation. According to EDS results pure YZO samples are obtained. Optical transmittances of all samples were investigated in the range of 350–750 nm at room temperature. The average optical transmittances of YZO samples in the visible region are approximately over 90%, but the transmittance starts to decrease for Zn 0.98 Y 0.02 O sample. Also, it was observed that the optical transmittances of Y-doped samples are higher than that of undoped ZnO. The electrical properties of YZO samples were obtained by resistance measurements at room temperature. The resistivity of samples was found to be 2.25 × 10 −3 , 1.43 × 10 −3 , 7.8 × 10 −3 , and 1.3 × 10 −3 Ω-cm for Zn 0.995 Y 0.005 O, Zn 0.99 Y 0.01 O, Zn 0.985 Y 0.015 O and Zn 0.98 Y 0.02 O, respectively. All these results show that surface, structural, electrical and optical properties of ZnO samples can be improved with doping Y up to 2 mol % concentrations.
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  • 5
    Publication Date: 2018-03-14
    Description: In this paper, we present the design and implementation of a type of yolk-like Fe 3 O 4 @C–Au@void@TiO 2 –Pd hierarchical microspheres with visible light-assisted enhanced photocatalytic degradation of dye and rapid magnetic separation. The resulting composite microspheres exhibited yolk-like hierarchical structures with a 236.3 m 2  g −1 surface area and a high-saturation magnetization of 31.5 emu g −1 . As an example of applications, the photodegradation of Rhodamine B (RhB) in the presence of NaBH 4 was investigated under simulated sunlight irradiation. The results show that the photocatalytic activity of the yolk-like Fe 3 O 4 @C–Au@void@TiO 2 –Pd microcomposites in the RhB photodegradation is higher than the Fe 3 O 4 @C–Au@void@TiO 2 and Fe 3 O 4 @C@TiO 2 microcomposites, as they can degrade RhB with 40 min of irradiation time. In addition, by magnetic separation, the as-prepared yolk-like Fe 3 O 4 @C–Au@void@TiO 2 –Pd hierarchical microcomposites can be completely separated and reused for four times.
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  • 6
    Publication Date: 2018-03-14
    Description: Fibrous Tb 3+ -doped TiO 2 were prepared using collagen fiber as template. Morphology, crystalline structure, surface area, element content, chemical composition and elemental chemical status, microstructure and element distribution of the prepared samples were characterized by using scanning electron microscopy, X-ray diffraction, specific surface area analysis, inductively coupled plasma atomic emission spectrometer, X-ray photoelectron spectroscopy, transmission electron microscope and element mapping, respectively. The photocatalytic activities were evaluated by following degradation of methyl orange. The results showed that the fiber structure of collagen template was fully preserved when the calcination temperature was 500–800 °C. However, with the increase of calcination temperature, crystallinity and average particle size were increased, and the photocatalytic performance was decreased. For 2% Tb 3+ –TiO 2 calcined at 500 °C, the degradation rate of methyl orange reached 93.87% after 6 h when a high-pressure mercury lamp (150 W) was used as the light source for photocatalytic degradation. Titanium tanning agent performance was excellent, the yield of TiO 2 was high, and the fiber structure was presented when 0.2 mol/L citric acid/sodium citrate buffer solution was used.
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  • 7
    Publication Date: 2018-03-14
    Description: A series of Ti species pillared HNbMoO 6 composites with different Ti/Mo ratios were prepared via an intercalation–pillaring route. The effect of Ti species on the photocatalytic performance of HNbMoO 6 and the reason were investigated by means of physicochemical methods such as powder X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), N 2 adsorption–desorption isotherms, laser Raman spectroscopy (LRS) and UV–Vis diffuse reflectance spectroscopy (UV–Vis DRS). The results showed that the effects of Ti species dosage on the disperse state, the interaction model, spectral response characteristic and photocatalytic performance were significant. When the Ti/Mo ratio was less than 1, Ti species were uniformly dispersed on the interlayer of HNbMoO 6 , and presented the obvious interaction with the host laminates. The specific surface area of the as-prepared Ti-HNbMoO 6 (with Ti/Mo ratio 1) was 4 times than that of the host material. The narrower band gap and more excellent photocatalytic performance of T1-HNbMoO 6 were derived from the obvious synergistic effect between the host and the guest.
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  • 8
    Publication Date: 2018-03-14
    Description: In this paper, the detailed device characteristics were investigated both before and after the Si 3 N 4 passivation grown by plasma-enhanced chemical vapor deposition (PECVD). Better transport properties have been observed for the passivated devices compared with the same ones before passivation. The strain variation and the influence of the scattering mechanisms were analyzed and studied. The calculated results show that the non-uniform distribution of the additional polarization charges at the AlGaN/AlN/GaN interfaces has been weakened by the deposition of the Si 3 N 4 layer. The numerical rise of the two-dimensional electron gas (2DEG) electron mobility and the decrease of the measured R on – A values were in a good consistency, and the weakening of the polarization Coulomb field (PCF) scattering after the passivation process is considered to be the main cause of these phenomena.
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  • 9
    Publication Date: 2018-03-14
    Description: Interaction of ultrafast laser pulses with metal surfaces in the spallation regime can result in the formation of anisotropic nanoscale surface morphology commonly referred to as laser-induced periodic surface structures (LIPSS) or ripples. The surface structures generated by a single pulse irradiation of monocrystalline Cr samples are investigated experimentally and computationally for laser fluences that produce high spatial frequency nanostructures in the multi-pulse irradiation regime. Electron microscopy reveals distinct response of samples with different crystallographic surface orientations, with (100) surfaces exhibiting the formation of more refined nanostructure by a single pulse irradiation and a more pronounced LIPSS after two laser pulses as compared to (110) surfaces. A large-scale molecular dynamics simulation of laser interaction with a (100) Cr target provides detailed information on processes responsible for spallation of a liquid layer, redistribution of molten material, and rapid resolidification of the target. The nanoscale roughness of the resolidified surface predicted in the simulation features elongated frozen nanospikes, nanorims and nanocavities with dimensions and surface density similar to those in the surface morphology observed for (100) Cr target with atomic force microscopy. The results of the simulation suggest that the types, sizes and dimensions of the nanoscale surface features are defined by the competition between the evolution of transient liquid structures generated in the spallation process and the rapid resolidification of the surface region of the target. The spallation-induced roughness is likely to play a key role in triggering the generation of high-frequency LIPSS upon irradiation by multiple laser pulses.
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  • 10
    Publication Date: 2018-03-14
    Description: In the present article, the hygro-thermal wave propagation properties of single-layered graphene sheets (SLGSs) are investigated for the first time employing a nonlocal strain gradient theory. A refined higher-order two-variable plate theory is utilized to derive the kinematic relations of graphene sheets. Here, nonlocal strain gradient theory is used to achieve a more precise analysis of small-scale plates. In the framework of the Hamilton’s principle, the final governing equations are developed. Moreover, these obtained equations are deemed to be solved analytically and the wave frequency values are achieved. Some parametric studies are organized to investigate the influence of different variants such as nonlocal parameter, length scale parameter, wave number, temperature gradient and moisture concentration on the wave frequency of graphene sheets.
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