1,308 research outputs found
Methomyl-resistant mechanisms of the oriental fruit fly, Bactrocera dorsalis (Diptera: Tephritidae)
No full textDirect Side Pumping of Double-Clad Fiber Laser by Laser Diode Array Through the Use of Subwavelength Grating Coupler
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Structure and electrical properties of silica-based polyethylene nanocomposites
No full textThe topic of polymer nanocomposites remains an active area of research in the dielectrics community, due to the unique electrical properties that these materials could exhibit. To explain the behaviour of these materials, the importance of clarifying the interfaces between nanoparticles and polymer matrices has been emphasised. However, understanding of the interface in nanocomposites is unsatisfactory and, consequently,many experimental results remain unexplained. This thesis reports on an investigation into a polyethylene nanocomposite system that contains varying amounts of nanosilica that differ with respect to their surface chemistry. The addition of nanosilica, even with different surface chemistries, was found to enhance the nucleation density of polyethylene and perturb the spherulitic development. While less organised lamellar structures would be expected to lead to a lower breakdown strength, this does not appear to be the case for the material systems considered here under alternating current (AC) fields. In addition, nanosilica filled polyethylene was found to absorb significantly more water than unfilled polyethylene, with the consequence that both the permittivity and the loss tangent increase with increasing duration of water immersion. However, appropriate surface treatment of nanosilica reduces the water absorption effect and modifies the dielectric response of the nanocomposites compared with those containing an equivalent amount of untreated nanosilica. Although water absorption may not be a technologically desirable characteristic, the results indicate that water molecules can act as effective dielectric probes of interfacial factors. Meanwhile, the direct current (DC) breakdown strength reduces with the inclusion of increasing amount of nanosilica in the polyethylene, but surface treatment of nanosilica improves the DC breakdown strength with respect to equivalent nanocomposites containing untreated nanosilica. Results from space charge studies reveal increased space charge accumulation in the presence of the untreated nanosilica and, upon surface treatment of the nanosilica, the charge development was suppressed in comparison with nanocomposites containing an equivalent amount of untreated nanosilica. This observation suggests that space charge accumulation and DC failure are related in these systems and it would seem that control of surface chemistry is particularly critical in connection with the use of nanocomposites in DC applications. Finally, the mechanisms underpinning the concept of filler functionalisation in nanocomposites were investigated via the use of different aliphatic chain length silane coupling agents, and the results show that long silane chains enhance the DC breakdown strength of the resulting nanocomposites. The possible further enhancement in DC breakdown strength is also highlighted. Overall, this thesis demonstrates how a nanoparticle’s interface chemistry can affect both the structure and the electrical properties of the resulting nanocomposites, and serves as an important foundation towards the engineering of nanocomposites as the reliable electricalinsulation materials of the future, through the understanding of the interface
The study of AlN thin film grown on bottom electrode under room temperature condition
No full textIn this study, highly C-axis oriented AlN thin films stacked upon Al bottom electrode on Si and Glass substrate are deposited with Reactive RF magnetron sputtering Technique. Three different sputtering systems were utilized to evaluate the optimized growth parameters. Room temperature growth was applied to the all system. During thin film growing , the substrate bias condition, sputtering work pressure, sputtering power and the N2 concentration are those key parameters to be adjusted in order to gain smooth surface morphology and highly C-axis prefer orientation AlN thin films.
The crystallography of the deposited films was analyzed by x-ray diffraction (XRD). Film surface morphology was characterized by scanning electron microscopy (SEM). Meanwhile, transmission electron microscopy (TEM) was adopted to observe the microstructure and determine the grain size of the film.
The results of the XRD patterns showed that in a 17cm long sputtering working distance condition, the AlN (002) can be obtained and the peak intensity can be increased when the sputtering power was fixed meanwhile reduced the working pressure and applied the negative bias on the substrate. The surface morphology can be improved with long working sputtering distance. The micrography of the TEM reveals that there is a transition region between Al metal and AlN film. Fine column structures can be observed in the initial growth stage. The size of the grain increased as the film became thicker. Strong AlN (002) ring pattern was obtained from the region of the top of the film. It indicates that the AlN (002) will not appear till the thickness of the film reach the critical thickness
Hybrid quantum dots /photonic crystal color tunable light emitting diodes
No full textWe demonstrate spectrally tunable hybrid photonic crystal Quantum Dots (QDs)LEDs. QDs are embedded into photonic crystals of GaN/InGaN LED for efficient color conversion. Color tunable LED has individually addressable LED module.</p
Tracing the chemical footprint of shocks in AGN-host and starburst galaxies with ALMA multi-line molecular studies
Get PDFMulti-line molecular observations are an ideal tool for a systematic study of
the physico-chemical processes in the Interstellar Medium (ISM), given the wide
range of critical densities associated with different molecules and their
transitions, and the dependencies of chemical reactions on the energy budget of
the system. Recently high spatial resolution of typical shock tracers - SiO,
HNCO, and CH3OH - have been studied in the potentially shocked regions in two
nearby galaxies: NGC 1068 (an AGN-host galaxy) (Huang et al., Astron.
Astrophys., 2022, 666, A102; Huang et al., in prep.) and NGC 253 (a starburst
galaxy) (K.-Y. Huang et al., arXiv, 2023, preprint, arXiv:2303.12685, DOI:
10.48550/arXiv.2303.12685). This paper is dedicated to the comparative study of
these two distinctively different galaxies, with the aim of determining the
differences in their energetics and understanding large-scale shocks in
dfferent types of galaxies.Comment: Accepted for publication in Faraday Discussions 2023. 18 pages, 7
figures and 2 table
Experimental Study of Noise Reduction and Improved Cooling Fan Performance in a PDP TV
No full textThe present experimenral study addresses fan system noise reduction and improvement in cooling performance in a plasma display panel(PDP) television (TV), The broadband noisr in a PDP TV is closely related to system losses. The system losses, mainly due to rear case of the TV near the fan, are reducced by increasing the number of vent holes in the case, preventing secindary leajage flow between the fan and the case and modifying the reat case shape. The discrete noise is mainly related with the inflow conditions therefore, the removal of structures that distort inflow results in a discrete noise reduction. Additionally, the fan rotationg speed is reduced because of the increased flow rate and reduced flow fluctuaion, shich is obtained from the reduction of system loss(resistance). 7.3dB(A) noisr reduction and a 10% increase in flow rate are achieved. rhe manin concepts behind realizing noise reduction are prevention of recirculation flow around rhe fan and reduction of sysrem loss.. The author wish to acknowledge the financial wupport of LG Electronics, Inc., and useful discussions with Dr, Suk Kwan Kim at LG-PRC
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