Modeling Of Vibration Transmission And Prediction Of Structure-Borne Noise In Buildings

Vibration originating from mechanical services are often the source of structure-borne noise in buildings. The transmitted vibration waves from the service equipment can propagate through the building structures and can eventually radiate sound which causes an audible low frequency noise causing disturbance inside the building. Models and discussions on of the vibration transmitted through the building structures are still lacking, particularly on how it is radiated as sound. This project proposes the development of firstly, a generic analytical model of a 2D portal frame structure consisting of column and beam elements. The results of the velocity of the structures are validated with those from Finite Element (FE) model.Bending waves in the building structure are presented through the operation deflection shapes diagram. Secondly, the 2D FE model is extended to a 3D FE model to include plate elements to represent walls, floors and roofs in a building. Using the hybrid FE/SEA analysis in VA One software, sound pressure level (SPL) in the building environment can be predicted using the injected power data of the motor obtained from the reception plate experiment. With the induction motor speed of 50 Hz, the overall SPL are 44 dB and 42 dB for the upper and lower cavities of the building respectively. These levels depend on the input power injected by the motor which is also directly affected by the mechanical faults in the motor i.e. mass unbalance and structural looseness. It is demonstrated that the SPL varies due to the faults in the motor. The result shows that the model can be applied as a preliminary predictive guide on the building design to minimize noise and vibration generated by service equipment

Electronic Conduction in Disordered Carbon Materials

Graphene, consisting of a single layer of carbon atoms, is being widely studied for its interesting fundamental physics and potential applications. The presence and extent of disorder play important roles in determining the electronic conduction mechanism of a conducting material. This thesis presents work on data analysis and modelling of electronic transport mechanisms in disordered carbon materials such as graphene. Based on experimental data of conductance of partially disordered graphene as measured by Gómez-Navarro et al., we propose a model of variable-range hopping (VRH) – defined as quantum tunnelling of charge carriers between localized states – consisting of a crossover from the two-dimensional (2D) electric field-assisted, temperature-driven (Pollak-Riess) VRH to 2D electric field-driven (Skhlovskii) VRH. The novelty of our model is that the temperature-dependent and field-dependent regimes of VRH are unified by a smooth crossover where the slopes of the curves equal at a given temperature. We then derive an analytical expression which allows exact numerical calculation of the crossover fields or voltages. We further extend our crossover model to apply to disordered carbon materials of dimensionalities other than two, namely to the 3D self-assembled carbon networks by Govor et al. and quasi-1D highly-doped conducting polymers by Wang et al. Thus we illustrate the wide applicability of our crossover model to disordered carbon materials of various dimensionalities. We further predict, in analogy to the work of Pollak and Riess, a temperature-assisted, field-driven VRH which aims to extend the field-driven expression of Shklovskii to cases wherein the temperatures are increased. We discover that such an expression gives a good fit to the data until certain limits wherein the temperatures are too high or the applied field too low. In such cases the electronic transport mechanism crosses over to Mott VRH, as expected and analogous to our crossover model described in the previous paragraph. The second part of this thesis details a systematic data analysis and modelling of experimental data of conductance of single-wall carbon nanotube (SWNT) networks prepared by several different chemical-vapour deposition (CVD) methods by Ansaldo et al. and Lima et al. Based on our analysis, we identify and categorize the SWNT networks based on their electronic conduction mechanisms, using various theoretical models which are temperature-dependent and field-dependent. The electronic transport mechanisms of the SWNT networks can be classed into either VRH in one- and two-dimensions or fluctuation-assisted tunnelling (FAT, i.e. interrupted metallic conduction), some with additional resistance from scattering by lattice vibrations. Most notably, for a selected network, we find further evidence for our novel VRH crossover model previously described. We further correlate the electronic transport mechanisms with the morphology of each network based on scanning electron microscopy (SEM) images. We find that SWNT networks which consist of very dense tubes show conduction behaviour consistent with the FAT model, in that they retain a finite and significant fraction of room-temperature conductance as temperatures tend toward absolute zero. On the other hand, SWNT networks which are relatively sparser show conduction behaviour consistent with the VRH model, in that conductance tends to zero as temperatures tend toward absolute zero. We complete our analysis by estimating the average hopping distance for SWNT networks exhibiting VRH conduction, and estimate an indication of the strength of barrier energies and quantum tunnelling for SWNT networks exhibiting FAT conduction

Development of multiplex-PCR for Genetically Modified Organism (GMO) detection targeting EPSPS and Cry1Ab genes in soy and maize samples

: The incidence of GMO is increasing worldwide therefore development of a reliable yet cost and time saving analytical method to detect GMO is important. This study aimed to develop a multiplex-PCR for GMO detection targeting Cry1Ab and EPSPS genes in soy and maize samples simultaneously, and secondly to obtain purified nucleic acids using CTAB DNA extraction method for conducting a GM specific analysis on various types of food samples. The multiplex PCR was optimized to improve PCR performance and to minimize failure. Out of 60 samples, 42 (70.0%) were found containing Cry1Ab or EPSPS genes, consisting of 11.9% of Roundup Ready Soya positive samples and 88.1% of Bt 176 Maize positive samples. Besides, 71.7% samples yielded DNA concentration above 50 ng/µl; 66.7% samples were in the DNA purity range of 1.6 to 2.0 and 85.0% of the samples were amplifiable for the endogenous gene screening. The CTAB DNA extraction method is effective for the DNA extraction from animal feeds, raw materials and processed foods

The Effect Of Perforation On The Dynamics Of A Flexible Panel

Introduction of holes into plate-like structures is commonly found as one of the practical noise control measures to reduce sound radiation. However, perforation also reduces the panel stiffness and hence increases its vibration. The discussion on this effect is lacking and hence this paper discusses the dynamics of a perforated panel from the results obtained from Finite Element (FE) model. Different hole geometries and arrangement are simulated to investigate their effect on the plate mobility. In general, it is found that increasing the perforation ratio increases the plate mobility. For a fixed perforation ratio, the mobility increases at high frequency (above 1kHz) for a smaller hole density in the plate. The plate with holes concentrated at the middle shows the largest increase of vibration around the plate centre compared to those uniformly distributed or away from the middle and concentrated at the plate edges. This is because as the hole separation becomes smaller, the reduction of the global stiffness around the mid area of the plate becomes greater. This also corresponds to the finding here that the mobility is greater at the vicinity of the hole. Different conditions of the plate edges are found to give consistent trend of the effect of perforation

Today's wastage is tomorrow's shortage: a systematic literature review on food waste from social responsibility perspective

PurposeRecognizing food waste as a global issue, it has attracted scholars to conduct numerous relevant studies in the area. Growing concerns about the social and environmental impacts have intensified food waste attention to the practice of socially responsible consumption. The purpose of this study is to undertake a review of existing knowledge to edify and provide a platform for future research.Design/methodology/approachThe present study retrieved and reviewed a total of 76 articles from Web of Science (WoS) database, which were published from 2011 to 2020 in food and nutrition related journals from social responsibility perspective.FindingsIn accordance with the proposed research questions, the findings demonstrate the publication trend, distribution of article sources, research regions, thematic classification, theoretical and methodology framework. The findings also reveal research gaps in the literature and facilitate scholars with extensive gap-specific research directions to explore.Research limitations/implicationsThis review is limited in its consideration of articles from the (WoS) database and focused in food or nutrition related journals.Originality/valueBy mapping what is known in the current state of food waste research, this study identifies existing gaps and opportunities for future research in this area.</jats:sec

Responses to Stress among East Malaysian Students : Psychometric Properties of the Responses to Stress Questionnaire

Background: Academic stress is part of a student’s life. Chronic stress may result in mental health problems, affecting the adolescent’s well-being in adulthood. However, not all types of stress result in a negative effect. Therefore, understanding how adolescents adapt to academic stress can lay the groundwork for preventive interventions. The Response to Stress Questionnaire (RSQ) for academic problems centred on a multidimensional model of responses to stress. However, it has not been tested among Malaysians. Thus, this study aimed to validate the questionnaire among Malaysians. Methods: The questionnaire was translated into the Malay language using forward and backward translation. Data were collected via self-administered questionnaires at a secondary school in Kuching. A validity test was conducted using face and content validation by subject matter experts, and construct validation was performed using exploratory factor analysis (EFA). A reliability test was conducted by checking Cronbach’s alpha. Results: Results showed that the questionnaire has good validity and reliability. The EFA resulted in only three dimensions of responses to stress among Malaysian adolescents in contrast to the five dimensions in the original RSQ for academic problems. The Cronbach’s alpha showed good reliability of the questionnaire. Conclusion: The questionnaire measuring responses to stress was valid and reliable in assessing the responses of adolescents to academic stress