The normal state resistivity of highTc Y-Ba-Cu-O compounds has been investigated and it is shown that the room temperature resistivity depends exponentially on
the volume fraction of the non-superconducting phase. It is further shown that the dependence of normal state resistivity
on temperature upto 300 K can be explained on the basis of a short-range co-operative electron-phonon coupling. This model
also explains the observed positive Seebeck coefficient for the pure phase superconducting sample. 相似文献
In the present paper, we have studied the self-focusing of a laser beam in a relativistic plasma. We have set up the non-linear
differential equation for the beam width parameter of the main beam by using the moment theory approach and solved it numerically
by the Runge–Kutta method. The results obtained are in agreement with the findings of the simulation (3D PIC). A new stable
form of self-channeling propagation has also been observed. 相似文献
The catalytic activity of hydrotalcite ([M(II)1−xM(III)x(OH2)]x+(CO32−)x/n·mH2O; where M(II) = Mg, Ni, Zn and M(III) = Al) was evaluated for the synthesis of jasminaldehyde by solvent free condensation of 1-heptanal with benzaldehyde. The effect of activation of as-synthesized Mg-Al hydrotalcite samples of varied Mg/Al molar ratio on its catalytic activity was studied and correlated with their basicity as determined from the model test reaction. The effect of reaction parameters such as, amount of catalyst, benzaldehyde to 1-heptanal molar ratio and reaction temperature on conversion of 1-heptanal and selectivity of jasminaldehyde was studied in detail. Maximum selectivity of jasminaldehyde (86%) with 98% conversion of 1-heptanal was observed using as-synthesized Mg-Al hydrotalcite of Mg/Al molar ratio of 3.5 as a catalyst. The kinetics of the reaction was measured and reaction rate and order of reaction were determined under optimum reaction conditions. The catalyst was re-used upto three cycles without significant loss in its activity. The base catalyzed reaction mechanism for condensation of 1-heptanal with benzaldehyde is proposed. 相似文献
Metallic substrates with ordered spherical cavities have been shown to be very effective for surface-enhanced Raman scattering (SERS) and can be fabricated reproducibly using electrodeposition. The sensitivity of detection is increased by several orders of magnitude by using surface-enhanced resonance Raman scattering (SERRS). In this report we demonstrate SERRS for the first time on electrodeposited gold films templated with colloidal spheres and demonstrate the reproducibility of the response. We also obtain a direct comparison between SERRS and SERS by choosing two dyes, Cy5 and Cy3, which are similar in structure but differ in their excitation maxima, such that one is resonant and the other non-resonant with our laser excitation. As expected, the resonant enhancement is found to be of the order of 10(3) over and above that for SERS. The net SERRS enhancements are shown to be of the order of 10(9). We also find that the resonant enhancement profile of the different peaks for the chromophore follows the plasmonic resonance absorption spectrum obtained for the structured surface. 相似文献
Palladium and platinum are important catalytic metals, and it would be highly advantageous to be able to use surface enhanced Raman spectroscopy (SERS) to study reactive species and intermediates on their surfaces. In this paper we describe the use of templated electrodeposition through colloidal templates to produce thin (<1 microm) films of palladium and platinum containing close packed hexagonal arrays of uniform sphere segment voids. We show that, even though these films are not rough, when the appropriate film thickness and sphere diameter are employed these surfaces give stable, reproducible surface enhancements for Raman scattering from molecules adsorbed at the metal surface. We report SERS spectra for benzenethiol adsorbed on the structured palladium and platinum surfaces of different thicknesses and void diameters and show that, for 633 nm radiation, enhancements of 1800 and 550 can be obtained for palladium and platinum, respectively. 相似文献
The present study demonstrates the development of a supramolecular porous ensemble consisting of hetero‐oligophenylene derivative 6 and Au‐Fe3O4 nanodots. Supramolecular assemblies of AIE‐active hetero‐oligophenylene derivative 6 served as reactors for the generation of Au‐Fe3O4 nanodots. The as prepared supramolecular ensemble functioned as an efficient recyclable photocatalytic system for C(sp2)?H bond activation of anilines for the construction of quinoline carboxylates. Interestingly, the “dip catalyst” prepared by depositing PTh‐co‐PANI‐6: Au‐Fe3O4 nanodots on a filter paper served as a recyclable strip (up to 10 cycles) for C?C/C?N bond formation reaction. 相似文献
In the quest to discover the properties of planar semiconductors, two‐dimensional molybdenum trioxide and dichalcogenides have recently attracted a large amount of interest. This family, which includes molybdenum trioxide (MoO3), disulphide (MoS2), diselenide (MoSe2) and ditelluride (MoTe2), possesses many unique properties that make its compounds appealing for a wide range of applications. These properties can be thickness dependent and may be manipulated via a large number of physical and chemical processes. In this Feature Article, a comprehensive review is delivered of the fundamental properties, synthesis techniques and applications of layered and planar MoO3, MoS2, MoSe2, and MoTe2 along with their future prospects. 相似文献
In this paper, we evaluate the bit error rate (BER) performance of a free-space optical satellite downlink by considering the atmospheric turbulence effects using binary shift keying subcarrier intensity modulation and differential phase shift keying subcarrier intensity modulation (DPSK-SIM). The performance of the link is enhanced using aperture averaging and receiver diversity. The closed form mathematical expressions of BER for BPSK-SIM and DPSK-SIM schemes are derived and analyzed. It is observed that on varying the turbulence level, the performance of the link degrades when the turbulence level increases. The improved BER of 10?12 and 10?10 at signal-to-noise ratio of 30 dB of the link for both BPSK-SIM and DPSK-SIM is obtained by using aperture averaging (aperture diameter, D?=?10 cm) and receiver diversity with optimal combining.