A New Empirical Model for Predicting the Sound Absorption of Polyfelt Article

A New Empirical Model for Predicting the Sound Absorption of Polyfelt Fibrous Materials for Acoustical Applications - Article Example Empirical models do not require detailed knowledge of the internal structure of the material nor are they derived from theoretical considerations. Delany and Bazley [1] showed that the values of the characteristic acoustic impedance and propagation coefficient for a range of fibrous materials, normalized as a function of frequency divided by flow resistivity could be presented as simple power law functions. Model for Impedance The model is based on numerous impedance tube measurements and is good for determining the bulk acoustic properties at frequencies higher than 250 Hz, but not at low frequencies [2,3]. The validity of this model for lower and higher frequencies was further extended by Bies and Hansen [4].Dunn and Davern [5] calculated new regression coefficients between characteristic acoustic impedance and propagation coefficient for low airflow resistivity values of polyurethane foams and multilayer absorbers. To that effect, engineers can obtain the absorption coefficient of sound at normal incidence by using the equation below: ZR = P0 * C0 (1 + C1 ((P0f)/r)-c2) The final model which comes as a derivative of the first model is Zt = (ZR + iZl)[coth(a + iB) * l] Zt = ZIR + iZIl Qunli [6] later extended this work to cover a wider range of flow resistivity values by considering porous plastic open-cell foams.Miki [7, 8] generalized the empirical models developed by Delany and Bazley for the characteristics acoustic impedance and propagation coefficient of porous materials with respect to the porosity, tortuosity, and the pore shape factor ratio. Moreover, he showed that the real part of surface impedance computed by the Delany’s model converges to negative values at low frequencies. Therefore, he modified the model to give it real positive values even in wider frequency ranges. Other empirical models include those of Allard and Champoux [9]. These models are based on the assumption that the thermal effects are dependent on frequency. The models wor k well for low frequencies. The Voronina model [10] is another simple model that is based on the porosity of a material. This model uses the average pore diameter, frequency and porosity of the material for defining the acoustical characteristics of the material. Voronina [11] further extended the empirical model developed for porous materials with rigid frame and high porosity, and compared it with that of Attenborough's theory. A significant agreement was found between their empirical model and Attenborough's theoretical model. Recently, Gardner et al. [12] implemented a specific empirical model using neural networks for polyurethane foams with easily measured airflow resistivity. The algorithm embedded in the neural networks substitutes the usual power-law relations. The phenomenological models are based on the essential physics of acoustic propagation in a porous medium such as their universal features and how these can be captured in a model [13]. Biot [14] established the theo retical explanation of saturated porous materials as equivalent homogeneous materials. His model is believed to be the most accurate and detailed description till now. Among the significant refinement made to Biot theory, Johnson et al. [15] gave an interpolation formula for â€Å"Dynamic tortuosity† of the medium based on limiting behavior at zero and infinite frequency. The dynamic tortuosity employed by Johnson et al. is equivalent to the structure factor introduced by Zwikker and Kosten [16] and therefore

Discuss the Careers of Teaching and Car Salesman Research Paper

Discuss the Careers of Teaching and Car Salesman - Research Paper Example I do have the panache to learn about the unique features of each model and brand I come across (Witkin 152). Should I be a car salesman, I will definitely be one who is quiet well informed about cars. Every good vocation begins with a deep interest, isn’t it (Bloom 26)? Besides, I am a very authentic talker and I do believe that anybody who comes to me with the intention of buying a car will certainly end up buying one (Andrews 247). I believe that sincerity and frankness are the ultimate credentials that make a good salesman (Shetty & Buehler 63). The other thing is that I am really good with numbers; however I really don’t know whether I will be able to convert my deftness and finesse with numbers into actual sales. One enticing factor is that if I end up being a great car salesman, at a later stage I can start my own car dealership. Pecuniary benefits do constitute an integral component of a great career. Well, one cannot expect to be a premium salesman right from th e start. Or perhaps, considering my astute skills and communication expertise, I can later on move to a career in real estate. Actually, the thing is that the more I ponder about a career in auto sales, the less convinced I feel about joining this profession. I should listen to my heart also. I think a career as a teacher will be the one that will do ample justice to my academic achievements and personal temperament. I do have the dedication to pursue a discipline with sincerity and dedication. One cannot teach what one does not know. In teaching a person needs to be proficient in the subject one teaches (Stronge 66). Besides, I have an academic bent of mind which continually nudges me to build on the understanding of the subjects I like (Aylett 75). Teaching will be a really suitable outlet for such academic dedication and sincerity. The other great personal attribute that supports my choice of teaching as a