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Backward wave oscillation suppression study of the helix travelling wave tube
摘要： In this paper, the effect of backward wave oscillation (BWO) on helix slow wave structure performance for TWT has been described. In this paper both the cases tapered and untapered helix slow wave structure (SWS) have been analyzed, caused by BWO for high gain helix TWT. In house developed the one-dimensional (SUNRAY-1D) large signal analysis model has been used for stability analysis of the helix SWS. The analysis on backward wave amplifier gain has been carried out as a function of the taper parameter and frequency parameter. The position and nature of tapering also affect the electronic efficiency as well as the start oscillation current. Hence, position and nature of tapering have been optimized.
关键词： backward wave oscillation (BWO),support rods,instability,Slow wave structure (SWS)
更新于2025-09-23 15:23:52
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Structural, optical, and morphological stability of ZnO nano rods under shock wave loading conditions
摘要： Shock wave recovery experiment on crystalline materials is a hot research topic for aerospace applications. In this research article, authors present and demonstrate the stability of physical properties of ZnO nano rods (ZnO NRs) under shock wave loaded conditions. The test sample is synthesized by hydrothermal method and the shock waves were generated using a table top semi automatic pressure driven shock tube. A shock wave of 2.2 Mach number which has a transient pressure of 2.0 MPa and temperature 864 K was made to strike four test samples for the counts of 50,100,150 and 200, respectively. The shock loaded samples were subjected to XRD and optical analysis so as to understand the influence of shock waves in the structural and optical properties. The results show that ZnO NRs have magnificent molecular, optical, structural and morphological stability for 50,100 and 150 shocks. Though, when the number of shock pulses was increased to 200 and a blue shift was observed in UV-Vis spectrum, no changes in structural properties took place which was evidenced from XRD. From this shock wave recovery experiment, it is clear that ZnO NRs are highly stable against shock waves and hence this material is suggested for the aerospace and military applications.
关键词： ZnO nano rods,Aerospace applications,Structure stability,Shock waves
更新于2025-09-23 15:23:52
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Giant-Shell CdSe/CdS Nanocrystals: Exciton Coupling to Shell Phonons Investigated by Resonant Raman Spectroscopy
摘要： The interaction between excitons and phonons in semiconductor nanocrystals plays a crucial role in the exciton energy spectrum and dynamics, and thus in their optical properties. We investigate the exciton-phonon coupling in giant-shell CdSe/CdS core-shell nanocrystals via resonant Raman spectroscopy. The Huang-Rhys parameter is evaluated by the intensity ratio of the longitudinal-optical (LO) phonon of CdS with its first multiscattering (2LO) replica. We used four different excitation wavelengths in the range from the onset of the CdS shell absorption to well above the CdS shell band edge to get insight into resonance effects of the CdS LO phonon with high energy excitonic transitions. The isotropic spherical giant-shell nanocrystals show consistently stronger exciton-phonon coupling as compared to the anisotropic rod-shaped dot-in-rod (DiR) architecture, and the 2LO/LO intensity ratio decreases for excitation wavelengths approaching the CdS band edge. The strong exciton-phonon coupling in the spherical giant-shell nanocrystals can be related to the delocalization of the electronic wave functions. Furthermore, we observe the radial breathing modes of the GS nanocrystals and their overtones by ultra-low frequency Raman spectroscopy with nonresonant excitation, using laser energies well below the band gap of the heteronanocrystals, and highlight the differences between higher order optical and acoustic phonon modes.
关键词： Giant-shell nanocrystals,acoustic phonons,Dot-in-rods,Raman spectroscopy,Core-shell heterostructures,exciton-phonon coupling
更新于2025-09-23 15:23:52
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Axiolitic ZnO rods wrapped with reduced graphene oxide: Fabrication, microstructure and highly efficient microwave absorption
摘要： Axiolitic Zinc oxide/reduced graphene oxide (ZnO/r-GO) hybrid was achieved by a facile one-step hydrothermal route in this work. The axiolitic ZnO rods with uniform size were equally implanted in r-GO nanosheets. The composites exhibit prominent microwave absorption performance with the Min. RL of -55.7 dB for a thickness of merely 2.0 mm and effective absorption bandwidth covering the whole Ku band, which benefits by the introducing of axiolitic ZnO rods and constructing distinct structures. The synergistic effect of dipole polarization, interface polarization and conductivity manifestly boost the microwave attenuation capacity. The results indicated that the axiolitic ZnO/r-GO hybrid is a promising candidate for application in the field of microwave absorption, electromagnetic interference shielding, communication and safety information, etc.
关键词： polarization,microwave absorption,reduced graphene oxide,axiolitic ZnO rods
更新于2025-09-23 15:22:29
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Photothermal-Assisted Optical Stretching of Gold Nanoparticles
摘要： The synergy of photothermal energy and optical forces generated by tightly focused laser beams can be used to transform the shape of gold nanoparticles. Here, the combination of these two effects is demonstrated to be an effective way of elongating gold nanoparticles (Au NPs), massively tuning their plasmonic properties. The photothermal effect of the laser increases the temperature of Au NPs above the melting point, and optical forces deform the molten Au NPs. As a result, the shape of Au NPs transforms from nanospheres into nanorods or dimers, depending on the power and time of irradiation as well as the surface energy of the substrate. This process is reversible by using high laser power to transform nanorods back to nanospheres due to capillary dewetting. Such light-induced transformations of nanostructures not only provide a facile way to tune plasmon resonances but also shed light on how the synergistic effect of photothermal energy and optical forces works on plasmonic nanoparticles.
关键词： rods,films,dimers,optical forces,plasmons
更新于2025-09-23 15:21:21
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Liquid Crystalline Colloidal Mixture of Nanosheets and Rods with Dynamically Variable Length
摘要： Here, we demonstrate the novel double-component liquid crystalline colloids composed of mesogenic inorganic nanosheets and the rods with dynamically variable length controlled by temperature. As the length-controllable rod, stiff biopolymer microtubule is used, which was successfully polymerized/depolymerized from tubulin proteins through a biochemical process even in the presence of the nanosheets. The mesoscopic structure of the liquid crystal phase was reversibly modifiable as caused by the change of the rod length.
关键词： nanosheets,rods,temperature control,liquid crystalline colloids,dynamically variable length
更新于2025-09-23 15:21:01
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Angular and spatial color mixing using mixing rods with the geometry of a chaotic-dispersive billiard system
摘要： For mixing light from different colored LEDs, an optical color mixing system is required to avoid colored shadows and color fringes. Concerning the different color mixing systems, mixing rods are widespread as they provide very good spatial color mixing with high efficiency. The essential disadvantage of mixing rods, so far, is the lack of angular color mixing. The solution presented in this publication is the application of a chaotic-dispersive billiard’s geometry on the cross section of the mixing rod. To show both the spatial and the angular mixing properties of a square and a chaotic-dispersive mixing rod, simulations generated by the raytracing software ASAP are provided. All results are validated with prototype measurements.
关键词： chaotic billiards,LED color mixing,mixing rods
更新于2025-09-23 15:21:01
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Electric field-directed assembly of fullerene crystal rods into hierarchical films
摘要： Self-assembly of nanomaterials with desired material properties requires assembly control from nanometer to millimeter scales. Here, hierarchical C60 and C70 films are assembled from the nanoscale to macroscale by combining co-solvent precipitation with electric-field directed assembly. Fullerene molecular crystals are grown via seeded co-solvent precipitation with mixed organic solvents and antisolvent 2-propanol. Rods of varying aspect ratios (1.7, 2 and 3.7) are prepared as a function of injection volume, fullerene type and solution concentration. Electric fields are applied to colloidal fullerene rods confined to two dimensions. The applied field induces dipolar forces, dielectrophoretic forces, and electrohydrodynamic flows. Frequency-dependent phase transitions occur at the critical Maxwell–Wagner crossover frequency, where the effective polarizability of the particles in the medium is substantially reduced, resulting in changes in structure. Partial order phases form as a function of field strength, frequency, and confinement including tetratic, smectic, centered rectangular and string fluids.
关键词： colloidal rods,electric field,fullerene,hierarchical films,self-assembly
更新于2025-09-19 17:15:36
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Synthesis and characterization of rGO decorated cubic ZnTiO3 rods for solar light-induced photodegradation of rhodamine B
摘要： Cubic zinc titanate (ZTO) rods were synthesized via simple liquid precipitation method. The reduced graphene oxide/zinc titanate (rGO/ZTO) composites were prepared by using the synthesized ZTO rods and graphene oxide as precursors. The composites were characterized by thermogravimetric and differential scanning calorimetry (TG/DSC), X-ray diffraction (XRD) patterns, scanning electron microscope (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectra (XPS) and UV-vis diffuse reflectance spectra (UV-vis). The photocatalytic activity of the synthesized photocatalysts was evaluated by the degradation of rhodamine B (RhB) in water under sunlight irradiation. The results revealed that the rGO/ZTO composites exhibited higher photocatalytic activity than pristine ZTO. The rGO in rGO/ZTO composites preferentially accepted the photo-generated electrons as an electron reservoir, significantly reduced the chances of the recombination, and effectively prolonged the lifetime of holes in rGO/ZTO, therefore greatly enhancing the efficiency of hole-induced decomposition of dyes.
关键词： Rhodamine B,Cubic ZnTiO3 rods,Photocatalysis,rGO decorated
更新于2025-09-19 17:15:36
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Absence of Sigma 1 Receptor Accelerates Photoreceptor Cell Death in a Murine Model of Retinitis Pigmentosa
摘要： Sigma 1 Receptor (Sig1R) is a novel therapeutic target in neurodegenerative diseases, including retinal disease. Sig1R(cid:2)/(cid:2) mice have late-onset retinal degeneration with ganglion cell loss that worsens under stress. Whether Sig1R plays a role in maintaining other retinal neurons is unknown, but was investigated here using rd10 mice, a model of severe photoreceptor degeneration. METHODS. Wild-type, rd10, and rd10/Sig1R(cid:2)/(cid:2) mice were subjected to ERG and spectral-domain optical coherence tomography (SD-OCT) to assess visual function/structure in situ. Retinas imaged microscopically were subjected to morphometric analysis, immunodetection of cones, and analysis of gliosis. Oxidative and endoplasmic reticulum (ER) stress was evaluated at mRNA/protein levels. RESULTS. Photopic ERG responses were reduced signi?cantly in rd10/Sig1R(cid:2)/(cid:2) versus rd10 mice at P28 (31 6 6 vs. 56 6 7 lV), indicating accelerated cone loss when Sig1R was absent. At P28, SD-OCT revealed reduced retinal thickness in rd10/Sig1R(cid:2)/(cid:2) mice (60% of WT) versus rd10 (80% of WT). Morphometric analysis disclosed profound photoreceptor nuclei loss in rd10/Sig1R(cid:2)/(cid:2) versus rd10 mice. rd10/Sig1R(cid:2)/(cid:2) mice had 35% and 60% fewer photoreceptors, respectively, at P28 and P35, than rd10. Peanut agglutinin cone labeling decreased signi?cantly; gliosis increased signi?cantly in rd10/Sig1R(cid:2)/(cid:2) versus rd10 mice. At P21, NRF2 levels increased in rd10/Sig1R(cid:2)/(cid:2) mice versus rd10 and downstream antioxidants increased indicating oxidative stress. At P28, ER stress genes/proteins, especially XBP1, a potent transcriptional activator of the unfolded protein response and CHOP, a proapoptotic transcription factor, increased signi?cantly in rd10/Sig1R(cid:2)/(cid:2) mice versus rd10. CONCLUSIONS. Photoreceptor cell degeneration accelerates and cone function diminishes much earlier in rd10/Sig1R(cid:2)/(cid:2) than rd10 mice emphasizing the importance of Sig1R as a modulator of retinal cell survival.
关键词： cones,retinal neuroprotection,rods,retinal degeneration,rd10 mouse,ERG
更新于2025-09-19 17:15:36