1,096 research outputs found
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
蘋果樹基吸芽對葉蟎及其捕食蟎密度與分散之影響
No full textThe results from Perry apple orchard (in northern Utah, 1992) show that the spider mites could migrate from ground vegetation through tree root sucker, tree trunk, and then into tree canopy. Leaves of root sucker let the overwintering spider mite establish their first population there, and did appear to contribute to the higher spider mite densities in tree canopy The total percentage of spider mites was found higher and the relative density of total predatory mites was found lower in treatments with root suckers. The movement in mid-July and outbreak in early August of mites might be due to disturbed cultivation on ground covers. In addition, the score method used in this experiment could give the similar population density estimates.
依1992年在北猶他蘋果園所作之調查，顯示葉蟎之族群可從地上植被經由樹基之吸芽及樹幹，然後遷移至樹冠之葉片上。位於樹基之吸芽葉片，能提供越冬蟎類於春天開始活動時之棲所與取食需求，進而造成以後樹上蟎類的大發生。整體而言，在留有吸芽之樹上，可發現較高比率之葉蟎數，而其捕食蟎之密度相對較低。在7月中旬之蟎類大發生與大遷移，可能與地面植被之耕培行為有關。另外，
在本試驗中所使用之積分估算法，能相當準確的估算蟎數
The Problem of Rhizomata in the Pre-socratic Period
No full textUnlike the problems of Arche the Pre-socratic philosophers discussed the elements of the material world in the rhizomata questions.
This article is divided into three main parts. The first part deals with the historical development of the problems of rhizomata proceeding in the order of pluralism, mechanism and teleology. In the second part we investigate the essential contents of rhizomata operating from Empedocles, Democritus and Anaxagoras. The causal principle took place in the transcendental and immanental sophistication, and at the same time the materialistic and the idealistic Weltanschauung have had their origin and their na?ve forms. Finally, in the third part, the contemporary significance is discussed in the light of Aristotle’s metaphysical point of view. The author tries here to raise some questions about the foundations of the oppositional atmosphere of the Materialism and the Idealism today, which seems to have their origin from the Pre-socratic period
Optimum structures of digital controllers in sampled-data systems: a roundoff noise analysis
Full text linkIn this paper, the effect of roundoff noise in a digital controller is analyzed for a sampled-data system in which the digital controller is implemented in a state-space realization. A new measure, called averaged roundoff noise gain, is derived. Unlike the traditionally used measure, where the analysis is done based on an equivalent digital control system, this newly defined averaged roundoff noise gain allows us to take consideration of the inter-sample behavior. It is shown that this measure is a function of the state-space realization. Noting the fact that the state-space realizations of a digital controller are not unique, the problem of optimum controller structure is to identify those realizations that minimize the averaged roundoff noise gain subject to the -scaling constraint which is for preventing the signals in the controller from overflow. An analytical solution to the problem is presented and a design example is given. Both theoretical analysis and simulation results show that the optimum controller realizations obtained with the proposed approach are superior to those obtained with the traditional analysis based on a digital control system
A Study on the Social Philosophy in the Period of the Republic of China
No full textThis study is divided into three main parts, and additionally includes an introduction, conclusion, footnotes and reference books.
The first part deals with the historical development of the social philosophy in the period of the Republic of China. It begins from the revolutional ideology created by Dr. Sun Yat－sen in 1895, through the revolution in 1911, and ended in 1949, when the republic government escaped from mainland China to Taiwan on the one hand, it proppounded by scholars on the other.
The second part examines the essential contents of the social principles, problems and praxis during this century.
Finally in the third part the author attempts a critique on the values and the limitations of this study of the social philosophy in this period
Hybrid evolutionary algorithm with Hermite radial basis function interpolants for computationally expensive adjoint solvers
No full textIn this paper, we present an evolutionary algorithm hybridized with a gradient-based optimization technique in the spirit of Lamarckian learning for efficient design optimization. In order to expedite gradient search, we employ local surrogate models that approximate the outputs of a computationally expensive Euler solver. Our focus is on the case when an adjoint Euler solver is available for efficiently computing the sensitivities of the outputs with respect to the design variables. We propose the idea of using Hermite interpoloation to construct gradient-enhanced radial basis function networks that incorporate sensitivity data provided by the adjoint Euler solver. Further, we conduct local search using a trust-region framework that interleaves gradient-enhanced surrogate models with the computationally expensive adjoint Euler solver. This ensures that the present hybrid evolutionary algorithm inherits the convergence prperties of the classical trust-region approach. We present numerical results for airfoil aerodynamic design optimization problemss to show that the proposed algorithm converges to good designs on a limited computational budget
The Idea of the Philosophy of Education by Lao-tzu and Chuang-tzu
No full textThe purpose of the Taoist education is to create a perfect person. A perfect person means here "Ultimate man, Spirit-like man, Sage-minded man". The way to educate a man to be perfect by Lao-tzu is to "Convey his instructions without the use of speech".(行不言之教); for Chuang-tzu however is to use the Allegories(寓言之教). Both are the via negativa compared to the Confucian method, which seems to be via positiva.
It is wellknown that both Tao-te-ching and the Book of Chuang-tzu use the way of negation, which denegates graduately their desires, their sensations, even their own existences in order to transcend themselves to unificate with Tao, the ultimate cosmic principle. The perfect man means here the man who engages union with Tao.
Not just like the confucianits, who maintain the necessities of training all the virtues to cultivate oneself to be a saint or a sage, the Taoists bracket out of all particular virtues, make focus only in the "Union with Tao" as the only virtue. Here the "Union with Tao" has both the cosmological and ontological meaning.
The author tries to explain the above-mentioned idea in three main parts. The first part deals with the historical development of the via negative from Laotzu to Chuang-tzu. The second part deepens its form to the essential contents of this educational idea. Finally, in the third part the contemporary meaning of the Taoist educational theory will be discussed
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