1,266 research outputs found
Highly-accurate real-time syntonization using a GPS single-frequency receiver with an intelligent atmosphere forecasting model
No full text
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
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
Indium Phosphide Based Indium Arsenide Quantum Dot Infrared Photodetectors
No full textBased on the developed QD growth techniques, photoconductive InAs/InAlGaAs/InP QDIPs grown on InP by MBE technique were presented. These devices demonstrated responses to normal incident photoexcitations in the 5-18-mum range. The QDIP device based on bound-to-bound transitions shows a peak responsivity of 113 mA/W and a detectivity of 1.8 x 10 9 cmHz1/2/W at 10 K for a 10-period QD heterostructure. The device based on bound-to-continuum transitions demonstrates an improved dark current characteristics and a better detectivity of 2.1 x 10 9 cmHz1/2/W.Made available in DSpace on 2015-09-25T20:08:58Z (GMT). No. of bitstreams: 2
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Previous issue date: 2005Embargo set by: Seth Robbins for item 82233
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Reason: Restricted to the U of I community idenfinitely during batch ingest of legacy ETDsRestricted to the U of I community idenfinitely during batch ingest of legacy ETDsU of I Only104 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2005
Fabrication of Gallium Indium Arsenide Phosphide Quantum Wire Heterostructures for Optoelectronic Applications
No full textThermal annealing techniques were also applied to QWRs. After this treatment, emissions were found to be at a higher energy than the as-grown samples, attributed to the disordering of the lateral composition modulation which, in effect, raised the bandgap energy of the QWR material. In addition, annealing was also found to reduce the magnitude but maintain the direction of a red-shift in emission wavelength with cooling measurement temperature. This thermal treatment served to be a useful tool in engineering the emission wavelength from a QWR sample from 1.6 to 1.55 mm.Made available in DSpace on 2015-09-25T20:10:06Z (GMT). No. of bitstreams: 2
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Previous issue date: 1997Embargo set by: Seth Robbins for item 82498
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Reason: Restricted to the U of I community idenfinitely during batch ingest of legacy ETDsRestricted to the U of I community idenfinitely during batch ingest of legacy ETDsU of I Only85 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1997
Compliant Epitaxy of Iii-V Compound Semiconductors for Optoelectronic Device Applications
No full textThe second technique uses a novel approach: very-low temperature molecular beam epitaxy (VLT-MBE) which involves growth of amorphous and polycrystalline materials. Using GaP and laterally oxidized AlAs materials, substrate independent DBRs were fabricated at wavelengths in both the visible spectrum, 480 nm to 550 nm, as well as those used in the telecommunications industry, 1310 nm to 1550 nm. In addition, VLTMBE-grown InGaP was used as a protection layer during post-growth oxidation processes. These InGaP layers were used to protect the In0.25Ga0.75As layers, mentioned above, during the lateral oxidation relaxation process. The VLT-grown InGaP films were found to be superior to other protection layers, such as SiNx and SiO 2, due to their ability to allow dislocation reduction during the oxidation process. Because of the nature of the VLT-grown materials, they can be used in any material system using a variety of host-substrates, making this growth technique highly adaptable and useful.Made available in DSpace on 2015-09-25T20:08:04Z (GMT). No. of bitstreams: 2
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Previous issue date: 2002Embargo set by: Seth Robbins for item 82051
Lift date: Forever
Reason: Restricted to the U of I community idenfinitely during batch ingest of legacy ETDsRestricted to the U of I community idenfinitely during batch ingest of legacy ETDsU of I Only86 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2002
Probing Landau quantisation with the presence of insulator-quantum Hall transition in a GaAs two-dimensional electron system
No full textFabrication of Gallium Indium Arsenide Phosphide Quantum Wire Heterostructures for Optoelectronic Applications
No full text85 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1997.Thermal annealing techniques were also applied to QWRs. After this treatment, emissions were found to be at a higher energy than the as-grown samples, attributed to the disordering of the lateral composition modulation which, in effect, raised the bandgap energy of the QWR material. In addition, annealing was also found to reduce the magnitude but maintain the direction of a red-shift in emission wavelength with cooling measurement temperature. This thermal treatment served to be a useful tool in engineering the emission wavelength from a QWR sample from 1.6 to 1.55 mm.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD
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