Damping of double wall panels including a viscothermal air layer

This paper deals with the dynamic behaviour of double wall panels, with emphasis on damping and sound radiation. It will be shown that a narrow air layer separating the two plates of a panel significantly alters the mentioned quantities by its viscothermal properties. Numerical and experimental results will be presented for a double wall panel excited with a point force. Numerical results are obtained using a fully coupled vibro-acoustic finite element model. The air between the plates is modelled by special viscothermal elements. A very efficient frequency response method is used to determine the structural response to harmonic excitations. The radiated power is calculated with the help of socalled radiation modes. Experimental results are obtained using a special designed set-up. An electrodynamic shaker excites one panel and the excitation power is measured. The radiated sound power is measured with a sound intensity meter. The dissipated energy is determined by considering an energy balance. Typical parameters such as the distance between the plates and the ratio of plate thicknesses are varied. Numerical and experimental results agree fairly well. From the results it can be concluded that for narrow air layers, i.e. when the so called ’shear wave number’ is low, a large amount of energy is dissipated by viscothermal effects in the air layer

Business cycle synchronisation in the euro area: Developments, determinants and implications

The divergence of growth and inflation rates across EMU in recent years has reignited the debate as to whether Europe is really an "optimum currency area" in which monetary union yields net benefits. But answering this question is complicated inter alia by the further controversy over whether economic integration and, in particular, monetary union tend to cause convergence or divergence of business cycles. Past studies have found convergence under the Exchange Rate Mechanism (ERM) regime of the 1980s, but the final verdict on the 1990s and especially on the period since the start of EMU is still pending. Several studies, such as Böwer and Guillemineau (2006), compute the unweighted average of countries' bilateral correlations and find convergence in the 1990s and divergence since then, but this is largely caused by an outlier in Greece. We argue that similar to the treatment of inflation in monetary policy, for which a country's inflation rates are weighted by the relative size of a country's private consumption, one has to look at weighted GDP growth rates. Using these, we find synchronisation, i.e. a further increase in correlation, both during the 1990s and since the start of EMU, but only the former change is significant. These findings are subsequently confirmed by the development of inflation dispersion over time. We infer that, unlike during the run-up to EMU, the introduction of a common monetary policy itself has not brought about a great reduction in business cycle heterogeneity, and synchronisation will probably be limited in the coming years as well. This means that policy-makers at the national level need to do more to improve their economies' flexibility, in order to make them better able to cope with the remaining heterogeneity in output and inflation. --

Noise reduction by viscothermal acousto-elastic interaction in double wall panels

The present study focuses on the feasibility of noise reduction with double wall panels. The emphasis is put upon the application of the dissipative properties of a thin air layer between two flexible plates. Vibration energy is converted into heat by the viscosity and thermal conductivity of the air between the plates. The goal of this study is to develop and to validate efficient models including viscothermal wave propagation for double wall panels which make it possible to investigate the noise reduction for both airborne and structure borne noise at low frequencies

A fast vibro-acoustic response analysis method for double wall structures including a viscothermal air layer

The damping behaviour of a thin air layer between two flexible panels can be used to reduce sound radiation of structural excited panels. The numerical model of the double wall panels takes into account full acousto-elastic interaction and viscothermal wave propagation in the air layer. This means that the resulting system matrices are complex and frequency dependent which makes it difficult to perform response calculations. In this paper a very efficient calculation method is presented which is based on the superposition of uncoupled structural and acoustic eigenmodes. The frequency dependent behaviour is implemented by updating the reduced acoustic submatrices for each frequency step. The method is successfully implemented in the B2000 processor B2FRF

Aminopeptidase C of Aspergillus niger is a Novel Phenylalanine Aminopeptidase

A novel enzyme with a specific phenylalanine aminopeptidase activity (ApsC) from Aspergillus niger (CBS 120.49) has been characterized. The derived amino acid sequence is not similar to any previously characterized aminopeptidase sequence but does share similarity with some mammalian acyl-peptide hydrolase sequences. ApsC was found to be most active towards phenylalanine beta-naphthylamide (F-betaNA) and phenylalanine para-nitroanilide (F-betaNA), but it also displayed activity towards other amino acids with aromatic side chains coupled to betaNA; other amino acids with nonaromatic side chains coupled to either pNA or betaNA were not hydrolyzed or were poorly hydrolyzed. ApsC was not able to hydrolyze N-acetylalanine-pNA, a substrate for acyl-peptide hydrolases

Active vibration control for underwater signature reduction of a navy ship

Dutch navy ships are designed and built to have a low underwater signature. For low frequencies however, tonal vibrations of a gearbox can occur, which might lead to increased acoustic signatures. These vibrations are hard to reduce by passive means. To investigate the possibilities of active vibration control to reduce the underwater signature, a full scale experiment was performed with an active vibration control system on board of a navy ship. For this purpose six special, high efficiency, actuators were built and mounted on the gearbox. A MIMO adaptive feedforward control system was used to reduce the tonal vibrations of the gearbox which were excited by the diesel engine. Vibrations onboard and underwater acoustic pressures were used to monitor the performance of the system during full scale runs on the underwater acoustic range in Bergen, Norway. It can be concluded that the system is able to reduce the vibration and the acoustic signature significantly

Trait anxiety and the neural efficiency of manipulation in working memory

The present study investigates the effects of trait anxiety on the neural efficiency of working memory component functions (manipulation vs. maintenance) in the absence of threat-related stimuli. For the manipulation of affectively neutral verbal information held in working memory, high- and low-anxious individuals (N = 46) did not differ in their behavioral performance, yet trait anxiety was positively related to the neural effort expended on task processing, as measured by BOLD signal changes in fMRI. Higher levels of anxiety were associated with stronger activation in two regions implicated in the goal-directed control of attention--that is, right dorsolateral prefrontal cortex (DLPFC) and left inferior frontal sulcus--and with stronger deactivation in a region assigned to the brain's default-mode network--that is, rostral-ventral anterior cingulate cortex. Furthermore, anxiety was associated with a stronger functional coupling of right DLPFC with ventrolateral prefrontal cortex. We interpret our findings as reflecting reduced processing efficiency in high-anxious individuals and point out the need to consider measures of functional integration in addition to measures of regional activation strength when investigating individual differences in neural efficiency. With respect to the functions of working memory, we conclude that anxiety specifically impairs the processing efficiency of (control-demanding) manipulation processes (as opposed to mere maintenance). Notably, this study contributes to an accumulating body of evidence showing that anxiety also affects cognitive processing in the absence of threat-related stimuli