Sound absorption and reflection with coupled tubes

This paper describes a special sound absorbing technique with an accompanying efficient numerical design tool. As a basis pressure waves in a single narrow tube or pore are considered. In such a tube the viscosity and the thermal conductivity of the air, or any other fluid, can have a significant effect on the wave propagation. An important aspect is that due to the viscothermal wave propagation sound energy is being dissipated. This has been applied to configurations consisting of a manifold of tubes, the so-called coupled tubes. A design strategy was developed to create broadband sound absorption for a wall with configurations of coupled tubes. The viscothermal wave propagation in tubes is accounted for in B2000 via one-dimensional T2.VISC and T3.VISC elements. Also further applications of coupled tubes are described: a network of small coupled tubes is used as a numerical representation of conventional sound absorbing material and increased damping of flexible plates connected to a small air layer is created with tubes coupled to this air layer

Noise reduction with coupled prismatic tubes

The present investigation focuses on an accurate description of sound absorption. Within this research a new technique to create sound absorption for a predefined frequency band has been developed. Additionally, a simple and efficient numerical model for conventional sound absorbing materials, such as glass wool or foams, has been formulated. It is also demonstrated that the newly gained insights are useful in applications not directly related to sound absorption

Size distribution of embryos produced by crystal-rod contacts

We performed contact nucleation experiments on the (010) face of potassium hydrogen phthalate (KAP) crystals growing in a stagnant supersaturated aqueous solution and determined - after a given growth time t - (ex situ) the crystal size distribution (CSD) of the secondary nuclei (which at t = 0 are called "embryos") by using a scanning electron microscope (SEM). The origin of the secondary nuclei could clearly be revealed (damage to the crystal surface). The CSD can be fitted with a log-normal distribution which is typical for many powders obtained by grinding. Minimum size and mean size can be quantitatively understood by elementary fracture mechanics

A novel technique for measuring the reflection coefficient of sound absorbing materials

A new method to measure the acoustic behaviour of sound absorbing material in an impedance tube is presented. The method makes use of a novel particle velocity sensor, the microflown, and a microphone. The so-called p·u method is compared to three other methods of which the two microphone technique is well known. It is shown that the combination of a microphone and a microflown provides direct information on the acoustic impedance, the sound intensity and the sound energy density. The experimental results are compared to the results obtained with the conventional impedance tube measurements. To be able to repeat the measurements in a reliable way a well described test sample with a quarter-wave resonator is used. Furthermore it is shown that the viscothermal effects on the wave propagation are important, i.e. for the quarter-wave resonator and to a lesser extent for the impedance tube itself

Long-term oral antibiotic treatment : why, what, when and to whom?

Antibiotics are typically prescribed as short courses for acute infections, in order to reduce bacterial load, shift the balance in favour of host defences and thus help to overcome infection. Over the past decade, however, interest in the long-term anti-inflammatory and immunomodulatory effects of selected antibiotics has been on the increase. Since the clinical effectiveness of erythromycin was reported in diffuse panbronchiolitis in the 1980s, the use of macrolides has been adopted into many other chronic inflammatory airway diseases characterised by frequent exacerbations, including cystic fibrosis (CF), non-CF bronchiectasis, COPD, severe noneosinophilic asthma, bronchiolitis obliterans after lung transplantation and organising pneumonia. In this chapter, we discuss the indications and limitations of long-term macrolide treatment in these chronic respiratory conditions

Histopathology and genetic susceptibility in COVID-19 pneumonia

The clinical features of COVID-19 range from a mild illness to patients with a very severe illness with acute hypoxemic respiratory failure requiring ventilation and Intensive Care Unit admission. Risk factors for a fatal disease include older age, respiratory disease, diabetes mellitus, obesity and hypertension. Little is known about the mechanisms behind observed episodes of sudden deterioration or the infrequent idiosyncratic clinical demise in otherwise healthy and young subjects. As in other diseases, the answer to some of these questions may in time be provided by genotyping as well careful clinical, serological, radiological and histopathological phenotyping, which enable mechanistic insights into the differences in pathogenesis and underlying immunological and tissue regenerative response patterns. We will aim to provide a brief overview of the existing evidence for such differences in host response and outcome, and generate hypotheses for divergent patterns and avenues for future research, by highlighting similarities and differences in histopathological appearance between COVID19 and influenza as well as previous coronavirus outbreaks, and by discussing predisposition through genetics and underlying disease