A Heuristic Reputation Based System to Detect Spam Activities in a Social Networking Platform, HRSSSNP Journal

A Heuristic Reputation Based System to Detect Spam Activities in a Social Networking Platform, HRSSSNP Journal
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A Heuristic Reputation Based System to Detect Spam Activities in a Social Networking Platform, HRSSSNP Journal

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Preface This book attempts to bring together the theory and practice of dielectric materials for different kind of industrial applications. Fragmented information on dielectric theory and properties of materials, design of equipment and state of the art in applications relevant to the manufacturing industry should be collated and updated and presented as a single reference volume. In this book relevant and useful information is presented in the quoted literature and covered by our key patent applications. As an Editor and also Author in this field, I am honored to edit this book written by a selected group of researchers. Marius Alexandru Silaghi University of Oradea, Oradea, Romania
Section 1
Polymeric Dielectric Materials
Chapter 1
Polymeric Dielectric Materials Zulkifli Ahmad Additional information is available at the end of the chapter http dx.doi.org 10.5772 50638
1. Introduction 1.1. Background and brief history The definition for dielectric constant relates to the permittivity of the material symbol use here . The permittivity expresses the ability of a material to polarise in response to an applied field. It is the ratio of the permittivity of the dielectric to the permittivity of a vacuum. Physically it means the greater the polarisation developed by a material in an applied field of given strength, the greater the dielectric constant will be. Traditionally dielectric materials are made from inorganic substances eg. mica and silicon dioxide. However polymers are gaining wider use as dielectric materials. This is due to the easier processing, flexibility, able to tailor made for specific uses and better resistance to chemical attack. As early as mid-60 s polymers eg polyvinyl fluoride 1 and aromatic-containing polymers 2 are used as dielectric materials in capacitors. Further improvement in organic film fabrication was established as revealed in US Patent 4153925. Polymers can be fabricated fairly easily into thin film by solution casting and spin coating, immersion in organic substrate, electron or UV radiation and glow discharge methods. This is mainly due to lower thermal properties such as glass transition and melting temperature which contribute to a lower temperature processing windows. Their solubility is controllable without offsetting their intrinsic properties. In the case of inorganic material and ceramic, they have much higher thermal properties hence temperature requirement leads to an extreme end of processing temperatures. On the other hand polymers cannot stand too high a temperature. Their coefficient of thermal expansion is relatively larger than ceramic materials and susceptible to atmospheric and hydrolytic degradation. Table 1 shows the values of dielectric properties of several polymers with comparisons with several inorganic materials. Inorganic ceramics materials have higher dielectric constant than polymers. Water has a relatively high dielectric constant. This is quite cumbersome as any traces of moisture