Acoustic Absorbers and Diffusers

Abstract

Background: Cognitive Muscular TherapyTM (CMT) is an integrated behavioural intervention developed for knee osteoarthritis. CMT teaches patients to reconceptualise the condition, integrates muscle biofeedback and aims to reduce muscle overactivity, both in response to pain and during daily activities. This nested qualitative study explored patient and physiotherapist perspectives and experiences of CMT.Methods: Five physiotherapists were trained to follow a well-defined protocol and then delivered CMT to at least two patients with knee osteoarthritis. Each patient received seven individual clinical sessions and was provided with access to online learning materials incorporating animated videos. Semi-structured interviews took place after delivery/completion of the intervention and data were analysed at the patient and physiotherapist level.Results: Five physiotherapists and five patients were interviewed. All described a process of changing beliefs throughout their engagement with CMT. A framework with three phases was developed to organise the data according to how osteoarthritis was conceptualised and how this changed throughout their interactions with CMT. Firstly, was an identification of pain beliefs to be challenged and recognition of how current beliefs can misalign with daily experiences. Secondly was a process of challenging and changing beliefs, validated through new experiences. Finally, there was an embedding of changed beliefs into self-management to continue with activities. Conclusion:This study identified a range of psychological changes which occur during exposure to CMT. These changes enabled patients to reconceptualise their condition, develop a new understanding of their body, understand psychological processes, and make sense of their knee pain.

A transformation approach for efficient evaluation of oscillatory surface integrals arising in three‐dimensional boundary element methods

“…This formulation therefore contains the same oscillatory terms as (12) but replaces the surface integral with a contour integral. Because of the reduced dimensionality, the numerical integration cost should therefore reduce from O k 2 for (12) to O .k/ for (14).…”

“…There are no additional limitations on element geometry (beyond what is usual in BEM), though the toolbox only implements these integrals for planar polygonal elements. Use of (15) is preferred in most cases, because it avoids issues associated with the boundary of the geometric visibility zone; however, (14) should be used if the oscillatory function is an evanescent wave and the distance from x to S j is significant (in this case illum j .x/ D 0/. (19) and (20) allow results from the standard single and double layer potentials to be computed from the aforementioned points.…”

“…The solid angle term is of course independent of k j , meaning that the formulation in (15) is devoid of issues across the geometric visibility boundary and is therefore numerically favourable compared with (14). It is interesting to note that it was the solid angle S j .x/ that was removed to give this numerically-robust edge kernel, because that is also what is subtracted in many regularisation schemes for the hyper-singular operator (e.g.…”

Reverberation chamber and its verification for acoustic measurements

“…In an attempt to avoid this regrettable phenomenon, it was applied a combination of two different geometric types of boundary diffusers (the tent and semicylinder type) and curved plexiglasses as hanging diffusers (see Figure 1). Generally, the diffusers can be used to break up the reflected wavefront and so disperse the focus while still maintaining the acoustic energy and avoiding absorption, however, it should be remembered that diffusers surface can cause significant diffraction from its edges [8]. The amount of diffraction depends on the wavelength and the size of the obstacle [9].…”

“…For boundary diffusers, this means using two different diffusers abreast and arranging them randomly or pseudorandomly on the wall. This will reduce periodicity and so improve dispersion [8].…”