1,723,022 research outputs found
Shock isolation systems incorporating Coulomb friction
No full textThis study investigates a novel approach to the problem of shock isolation. The questions considered are whether friction produces a better performance in terms of reduced response during a shock compared to viscous damping and a lower residual response after the shock.To gain physical insight, a single degree of freedom model with friction applied to the isolated mass is analysed. It serves as a benchmark to the performance of a two degree of freedom model where friction is applied to a secondary mass. The isolation system performance is then quantified. For the two degree of freedom system with an intermediate secondary spring which connects the primary and secondary mass, it is possible to obtain the reduction in the displacement response as good as the single degree of freedom system and at the same time smoother acceleration response compared to the single degree of freedom system. For the purpose of further improvement, a control strategy is introduced to switch on and off friction in both models depending on some response parameters and this is compared to the passive systems. This is the semi active control strategy where friction is changed within a cycle of vibration (discontinuous). The control strategy provides more displacement reduction to ensure the maximum displacement response is much smaller than the base input which cannot be obtained with the passive systems.The practical implementation and experimental validation is presented only for the first stage of the response during the shock. For the practical implementation of the switchable friction, an electromagnet is applied to separate the friction surfaces. Good agreement with the simple theoretical models for both passive and switchable systems is obtained. The reduced displacement and smooth acceleration response were obtained from the experiments with the system used to represent the two degree of freedom model. The issues and limitations in the practical implementation are identified and discussed
A friction control strategy for shock isolation
No full textA control strategy is presented incorporating friction which can be adapted within a cycle of vibration. During base shock input, the friction is switched on and off based on specified response parameters. The predicted response of a semi active system is compared with that of a passive isolation system. The strategy is shown to produce an improved displacement reduction and a smaller maximum displacement compared to the base input; a result which cannot be obtained with a typical passive system. The models are then validated using an experimental rig, representing a two degree of freedom system, having an electromagnet to switch on and off friction via the control logic. Good agreement is obtained in addition to identifying optimum parameter choices
Al-falah acuan pembinaan negara bangsa dalam kalangan pelajar UPM
No full textAgenda pembinaan negara-bangsa Malaysia merupakan satu aspirasi yang relatif signifikan dalam merealisasi pembentukan satu bangsa satu negara berpaksikan kepada platform nasional. Proses pembentukan negara-bangsa menjadi pemangkin kepada tindakan afirmatif untuk mencapai perpaduan, kesepaduan, penyatupaduan dan kesatuan yang holistik dalam kalangan masyarakat kepelbagaian di Malaysia. Persoalan ini merupakan suatu perkara yang agak rumit, sentiasa dibahaskan dari pelbagai sudut pandang dan belum mencapai titik noktahnya. Kita sedia maklum bahawa masyarakat Malaysia terbentuk dari beberapa kumpulan etnik yang diwarisi dari pelbagai keturunan, mempunyai pegangan agama dan kepercayaan yang berbeza, mengamalkan sosio-budaya yang berbeza-beza dan pertuturan bahasa ibunda juga berbeza-beza. Perbezaan yang wujud dalam masyarakat bukanlah suatu perkara yang baharu tetapi telah cukup sinonim dalam realiti kehidupan bermasyarakat di negara ini. Perbezaan ini seandainya tidak ditadbir urus dengan baik, sudah pasti boleh mengundang pelbagai bentuk ancaman kepada negara seperti konflik etnik, percanggahan dan pertembungan, diskriminasi, streotaip, keganasan, genocide dan pelbagai lagi
Material plastic properties characterization by coupling experimental and numerical analysis of small punch beam tests
No full textA novel small punch beam testing (SPBT) system consisting of a top die, a bottom die and a flat punch with semi-circular cross-section head has been designed and tested. The specimen is a small beam with rectangular cross-section. This SPBT method has the advantage over conventional tensile testing for much less material required for testing and also over the traditional small punch testing because not only less material required but also high accuracy to make the punch head. Through coupling the numerical modelling and experimental results, genetic algorithm has been employed to successfully characterize the material plastic properties
Relative trade advantages of Malaysian shrimp products amongst the regional competitors.
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Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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