Browsing by Author "Dimitriadis, Emilios K."

Now showing 1 - 5 of 5
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    Active control of flexural power flow in elastic thin beams
    Gonidou, Luc-Olivier (Virginia Tech, 1988-02-05)
    Active control of flexural power flow in infinite, semi-infinite and finite beams by point force inputs has been analytically and experimentally studied. The systems were analyzed by assuming wave solution and then applying various terminating boundary conditions. Optimal control solutions were then obtained using a quadratic Wiener solution. The influence of system parameters such as discontinuity impedance and effects such as near fields, number and location of control actuators and error sensors is investigated and discussed. The mechanisms by which control is achieved are considered. It is demonstrated that the boundary conditions and the system configuration strongly influence the choice of optimal controller format. The experimental work is compared with the theoretical developments and found to be in good agreement. Control was achieved by a LMS Filtered-x algorithm implemented in assembler language on a TMS32020 digital signal processing chip. In general it is demonstrated that the flexural power flow in the beam types considered can be attenuated with a low number of active actuators.
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    Active control of noise transmission through rectangular plates using multiple piezoelectric or point force actuators
    Wang, Bor-Tsuen; Fuller, Chris R.; Dimitriadis, Emilios K. (Acoustical Society of America, 1991-11-01)
    This paper analytically demonstrates the use of multiple piezoelectric actuators bonded to the surface and point force actuators applied directly to a plate to reduce sound transmission through the plate. A harmonic plane wave incident on a simply supported, thin rectangular plate mounted in an infinite baffle was considered as the primary source. Both multiple piezoelectric and point force actuators are separately used as secondary (control) sources to attenuate the sound transmission through the plate. An optimal process was applied to obtain the input voltages of the piezoelectric actuators and the magnitude of the point forces, so that the radiated acoustic power can be minimized. Results show that a reduction of sound transmission through the plate is successfully; achieved, if the proper size, number, and position of the piezoelectric or point force actuators are selected. Additionally, a comparison showed that point force actuators provide more effective control of the sound transmission than piezoelectric actuators; however, piezoelectric patches have more practical implementation than point force shakers, because of their low cost and light weight.
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    A computational approach to the prediction of wheel wear profiles
    Wang, Bor-Tsuen (Virginia Tech, 1988-05-30)
    Wheel wear profiles are interesting for both economic and performance reasons. A good wheel profile design should be able to resist wear and to allow stable vehicle running. The ability to resist wear reduces the wheel reprofiling and replacement cost. The ability to allow stable vehicle running is important for safety and ride quality. In this work, a wear model based upon the work done in the wheel/rail contact patch is used to predict wheel wear profiles. The effects of train dynamic response, random rail alignment and the non-linearity of wheel/rail contact geometry are included The distribution of contact patch work is obtained by discretized method and applied to the wheel wear problem. Using the contact patch work wear model, consecutive wheel wear profiles for tread contact and slight flange contact are predicted. These analytical wear profiles match well with experimental results and other analytical approaches.
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    Protein Stability and Functional Characterization of Intra-Melanosomal Domain of Human Recombinant Tyrosinase-Related Protein 1
    Dolinska, Monika B.; Young, Kenneth L.; Kassouf, Claudia; Dimitriadis, Emilios K.; Wingfield, Paul T.; Sergeev, Yuri V. (MDPI, 2020-01-03)
    Pigmentation is the result of a complex process by which the biopolymer melanin is synthesized and packed into melanosomes of melanocytes. Various types of oculocutaneous albinism (OCA), a series of autosomal recessive disorders, are associated with reduced pigmentation in the skin, eyes, and hair due to genetic mutations of proteins involved in melanogenesis. Human tyrosinase (Tyr) and tyrosinase-related protein 1 (Tyrp1) drives the enzymatic process of pigment bio-polymerization. However, within the melanogenic pathway, Tyrp1 has catalytic functions not clearly defined and distinct from Tyr. Here, we characterize the biochemical and biophysical properties of recombinant human Tyrp1. For this purpose, we purified and analyzed the intra-melanosomal domain (Tyrp1tr) for protein stability and enzymatic function in conditions mimicking the environment within melanosomes and the endoplasmic reticulum. The study suggests that Tyrp1tr is a monomeric molecule at ambient temperatures and below (<25 °C). At higher temperatures, >31 °C, higher protein aggregates form with a concurrent decrease of monomers in solution. Also, Tyrp1tr diphenol oxidase activity at pH 5.5 rises as both the pre-incubation temperature and the higher molecular weight protein aggregates formation increases. The enhanced protein activity is consistent with the volume exclusion change caused by protein aggregates.
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    Vibration localization and statistical energy analysis in coupled systems
    Ezanno, Philippe (Virginia Tech, 1990-05-15)
    An investigation of the effect of the coupling value and the structural perturbation parameter is conducted on coupled systems. The analysis of a coupled pendulums system results in the analytical expression of the natural frequencies of the system. The response of the system for harmonic excitation and random input is developed. Two single Euler-Bemouilli beams coupled by a torsional spring constitute the multi degree of freedom extension of the study. Special care is given to show the variation of the natural frequencies \with the two parameters and modal overlapping is shown. The study of the response to harmonic excitation makes the localization phenomenon apparent. For the special case where one of the beam is excited by a rain-on-the roof load, the estimates of the amplitude for each beam and the power flow between the beams are analytically expressed. The power flow is proved to be concentrated around the natural frequencies, stronger for a tuned system and sensitive to the number of modes, especially v:hen modal overlapping occurs. A Monte Carlo simulation considering the perturbation parameter as a Gaussian random variable points out that the mean value of the power decreases rapidly with higher frequency. The power flow is also calculated using the theory of the Statistical Energy Analysis.