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Recent Advances in Acoustic Metamaterials for Simultaneous Sound Attenuation and Air Ventilation Performances

In the past two decades, acoustic metamaterials have garnered much attention owing to their unique functional characteristics, which are difficult to find in naturally available materials. The acoustic metamaterials have demonstrated excellent acoustical characteristics that paved a new pathway for researchers to develop effective solutions for a wide variety of multifunctional applications, such as low-frequency sound attenuation, sound wave manipulation, energy harvesting, acoustic focusing, acoustic cloaking, biomedical acoustics, and topological acoustics.

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Dual-functional metamaterial with vibration isolation and heat flux guiding

Metamaterials can provide many engineering applications such as vibration attenuation and heat flux cloaking. However, the problems of isolating elastic waves and directing heat flux via a metamaterial device have not been resolved completely yet. In this paper, a dual-functional metamaterial, with cylindrical stub periodically attached on the multilayered plate, is initially designed and investigated numerically and experimentally. Numerical results demonstrate that the elastic wave band gaps can be opened and tuned effectively with the evolution of the rotation angle of the matrix plate.

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Effects of long-duration wearing of N95 respirator and surgical facemask: a pilot study

The protection efficacy of facemasks and respirators has been well documented. The change of human nasal functions after wearing N95 respirator and surgical facemask is not known. In a parallel group study, we recruited 87 healthy healthcare workers. Each of the volunteers attended two sessions, and wore N95 respirator in session 1 (S1) and surgical facemask in session 2 (S2) for 3hours. Mean minimum cross sectional area (mMCA) of the two nasal airways via acoustic rhinometry and nasal resistance via rhinomanometry were measured before and immediately after the mask wearing.

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Objective Assessment of Increase in Breathing Resistance of N95 Respirators on Human Subjects

Face masks or respirators are commonly worn by medical professionals and patients for protection against respiratory tract infection and the spread of illnesses, such as severe acute respiratory syndrome and pandemic influenza (H1N1). Breathing discomfort due to increased breathing resistance is known to be a problem with the use of N95 respirators but there is a lack of scientific data to quantify this effect. The purpose of this study was to assess objectively the impact of wearing N95 face masks on breathing resistance.

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Labyrinthine acoustic metastructures enabling broadband sound absorption and ventilation

There is growing interest in the development of path coiling-based labyrinthine acoustic metamaterials for realizing extraordinary acoustical properties such as low-to-mid frequency sound absorption.

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Evaluation of rebreathed air in human nasal cavity with N95 respirator: a CFD study

The carbon dioxide level within N95 respirator is higher than without it, which needs a mechanical explanation. In the current study, we built a three-dimensional (3D) model of normal human nasal cavity to simulate the volume of fraction of both fresh air and respired air within the nasal cavity. The model consists of large rectangular domain outside the nasal cavity representing ambient air, human nasal cavity and partial of the pharynx. Two cases were simulated.

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Ventilated acoustic metamaterial window panels for simultaneous noise shielding and air circulation

The conflict between the acoustical performance and ventilation efficiency in conventional noise barriers limits their application potentials in several settings. To address this challenge, we design and experimentally demonstrate a ventilated tunable acoustic metamaterial for noise mitigation at targeted frequencies. Through the structure, a peak normal incidence sound absorption coefficient of more than 0.96 at 1000 Hz and the peak normal incidence sound transmission loss of 18 dB is achieved while maintaining the air circulation with a 45% open area of ventilation.

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Research Fellow/Research Assistant positions for mechanism design/vibration analysis of actuators for 10 Tbits/square HD Drives

Our group has two research openings for people with expertise on mechanism design / dynamic and vibration analysis of actuators cater to 10 Tbits/square inch hard disk drives. Please send your cv to me at mpeleehp@nus.edu.sg or Prof Ong CJ at mpeongcj@nus.edu.sg.

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Newton’s laws and a dynamic force-field analogy for analyzing organizational changes

The abstract of the paper is as follows (to appear in International Journal of Mechanical Engineering Education)

 A dynamic force-field analogy for analyzing organizational change is presented. Instead of

just analyzing the driving and restraining forces in the traditional force-field analysis, which is similar to

the static analysis in solid mechanics, the forces opposing change can be modeled in terms of viscous

or frictional forces that may be encountered. Some analogies between organizational change and the

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