Clinical and Nonclinical Health Care Workers Faced a Similar Risk of Acquiring 2009 Pandemic H1N1 Infection

(See the editorial commentary by Drumright and Holmes, on pages 284-286.) Reporting of confirmed pandemic influenza A virus (pH1N1) 2009 infection was mandatory among health care workers in Hong Kong. Among 1158 confirmed infections, there was no significant difference in incidence among clinical versus nonclinical staff (relative risk, 0.98; 95% confidence interval, 0.78-1.20). Reported community exposure to pH1N1 was common and was similar in both group

Coupled Decorated Membrane Resonators with Large Willis Coupling

We report the experimental studies on an acoustic scatterer consisting of a pair of coupled decorated membrane resonators (DMRs) that exhibits near extreme contrast in reflection asymmetry and strong Willis coupling coefficient with amplitude of 2.5 and polarizability cross term of 1.1 x 10-8 ms2. The design is based on the theoretical analysis using the Greens function formulism we developed earlier. The clean line shapes of the real and the imaginary parts of the Willis coefficient clear show, even by visual inspection, that the Kramers-Kronig relations are satisfied. Theoretical analysis agrees well with the major features of the experimental results

Sound and vibration absorption by decorated membrane resonators

Spongy and fibrillar materials have dominated the market of sound absorption over a decade. However, they fail to tackle the noise below 500 Hz. Therefore, absorption of low frequency sound becomes one of the most challenging topics in the acoustic field. This thesis introduces the use of decorated membrane resonator (DMR) in shielding and absorbing of low frequency noise below 1000 Hz. The acoustic characteristics of the DMR are shown in its resonance and anti-resonance modes. Under resonance modes, the transmission and absorption reach local maximum. The absorption coefficient of single layer DMR is theoretically bounded by 0.5. Under anti-resonance modes, the average membrane displacement is almost zero, hence the transmission drops to local minimum. The acoustic characteristics of the DMR can be modified by adding a sealed gas layer and a hard plate behind. This composition is so-called hybridized membrane resonator (HMR). By tuning the thickness of the sealed gas layer, the surface impedance of the HMR can match the impedance of air to achieve total absorption at anti-resonance. Moreover, the effective mass of a DMR grows significantly at its anti-resonance frequencies. This characteristic helps DMRs behave as good vibration dampers.</p

Low frequency sound absorption by decorated membrane resonators

For over a decade, spongy and fibrillar materials have dominated the sound absorption market. These materials, however, fail to tackle noise below 500Hz, and low frequency sound absorption remains one of the most challenging topics in the field of acoustics. This thesis discusses the use of decorated membrane resonators (DMRs) in shielding and absorbing low frequency noise below 1000Hz. DMRs possess unique acoustic characteristics in both its resonance and anti-resonance modes. In its resonance mode, both transmission and absorption of sound reaches a local maximum, and the absorption coefficient of a single layer of DMR is theoretically bounded by 0.5. In its anti-resonance mode, contrarily, the DMR membrane has an average displacement of almost zero, and transmission of sound drops to a local minimum. These acoustic characteristics of DMRs can be altered by adding a sealed layer of gas and a hard plate behind the membrane layer. This composition is a hybrid membrane resonator (HMR). By changing the thickness of the sealed gas layer, the HMR’s surface impedance can be tuned to match the impedance of air to achieve total sound absorption in its anti-resonance mode.</p