Investigation of selected properties of the black elder wood (Sambucus nigra L.)

Investigation of selected properties of the black elder wood (Sambucus nigra L.). The work has defined the selected chemical, physical and mechanical properties of the black elder wood, such as content of non-structural substances, shrinkage and density, speed of sound propagation, dynamic modulus of elasticity, acoustic resistance and sound attenuation, modulus of elasticity, bending strength, compressive strength, Brinell hardness, cold and hot-water extractives content and pH of hot-water extract. The black elder wood is hard and moderately shrinking. Mechanical properties are reduced by going from the pith to the perimeter, which is most likely affected by the increasing twist of the fibres. The distance from the pith also affects the acoustic properties and the size of the shrinkage, while the density remains constant.

Application and Verification of Time-Domain Impedance Boundary Conditions in CAA Simulations

In computational fluid dynamic (CFD) and computational aeroacoustics (CAA) simulations, the wall surface is normally treated as a purely reflective wall. However, some surface treatments are usually applied in experiments. Thus, the simulation results cannot be validated by experimental results. In aeroacoustics analysis, impedance is a quantity to characterize reflectivity and absorption of an acoustically treated surface. One of the major numerical challenges in CAA simulations is to define acoustically well-posed boundary conditions. The impedance boundary condition is a frequency-domain boundary condition. However, CFD and CAA simulations are time-domain computations, which means the frequency-domain impedance boundary condition cannot be adopted directly. Several methods, including the three-parameter model, the z-transform method and the reflection coefficient model, were developed. In the present study, a coupling method that combines the time-domain impedance boundary condition and Large Eddy Simulations (LES) is proposed. A channel flow with wall impedance is simulated at different acoustic resistance and reactance. The approach is verified by the case with purely reflective wall impedance. For the flow with wall impedance. The effects of acoustic resistance and reactance are investigated. It is found that the wall impedance contributes to the noise reduction in the near-wall region, and with the decrease of the resistance or reactance, the sound pressure level is decreased. The method developed in this study is expected to be applied to a variety of noise-control problems.

ON THE ACOUSTO-MAGNETIC METHOD OF MEASURING THE ACOUSTIC RESISTANCE OF LOCAL AREAS OF THE BIOLOGICAL TISSUE

The subject of study in the article is the acoustic resistance of local areas of the biological tissues in vivo, depending on their pathology. The aim of the work is to develop a quantitative method for measuring the acoustic resistance of local areas of the biological tissue (substance) located inside the human body. The following tasks are solved in the article: development of scientific foundations of the acousto-magnetic method for measuring the acoustic resistance of local areas of the biological tissue; development of a remote method for measuring electrical voltage on the surface of the patient's skin, caused by acousto-magnetic impact on local areas of the tissue and determined by the value of acoustic resistance; calculation of the ratios binding the value of the acoustic resistance of the local areas of the tissue with the electric voltage on the measuring probes on the patient's skin, the values of the acoustic radiation power and the external constant magnetic field, as well as with the distance between the probes and the local area of the biological tissue; verification of the calculated ratios using the experimental determination of the acoustic resistance of the local area of the model biological tissue. The following methods were used: physical modeling of the biological tissue, physical and mathematical modeling of electrical properties of the local part of the biological tissue, calculation of electromagnetic and acoustic parameters of the tissue, experimental measurement of electric field strength excited in the local part of the biological tissue, verification of calculated relations by comparing them with experimental results. The following results were obtained: the scientific foundations of the acousto-magnetic method for the quantitative measurement of the acoustic resistance of local areas of the biological tissue were developed; a remote method for measuring the electric voltage on the surface of the patient's skin caused by the acousto-magnetic effect on local areas of the tissue and the determined value of the acoustic impedance was developed; relations were calculated connecting the value of the acoustic impedance of local areas of the tissue with the electric voltage on the measuring probes on the patient's skin, the values of the acoustic radiation power and external constant magnetic field, as well as the distance between the probes and the local area of the biological tissue; verification of the calculated ratios was carried out using the experimental determination of the acoustic resistance of the local area of the model biological tissue. Conclusions: The scientific foundations of the remote acousto-magnetic method of high-precision measurement of the acoustic resistance of local areas of human biological tissue, confirmed experimentally on model tissue samples, have been developed. The method can make it possible to reveal with high accuracy the functional relations of the measured local value of acoustic resistance with pathological changes in the tissue. At the same time, the influence of the human factor on the interpretation of the recorded values of acoustic resistance (which is characteristic of the traditional, mainly qualitative, rather than quantitative ultrasound method) is excluded, the information content and reliability of acoustic diagnostics are increased.

A Perforated Plate with Stepwise Apertures for Low Frequency Sound Absorption

A perforated plate with stepwise apertures (PPSA) is proposed to improve sound absorption for low frequencies. In contrast with an ordinary perforated plate with insufficient acoustic resistance and small acoustic mass, the perforated plate with stepped holes could match the acoustic resistance of air characteristic impedance and also moderately increase acoustic mass especially at low frequencies. Prototypes made by 3D printing technology are tested in an impedance tube. The measured results agree well with that of prediction through theoretical and numerical models. In addition, an absorber array of perforated plates with stepwise apertures is presented to extend the sound absorption bandwidth due to the introduced multiple local resonances.

Instrumental Diagnosis Methods for ENT Diseases

As with any other clinical discipline, otorhinolaryngology uses both simple investigation methods including external examination of ENT organs with an otoscope, rhinoscope and laryngoscope, and more complex ones requiring the use of special devices and equipment. The latter include X-ray examination, US diagnostics, endomicroscopy of the nose and paranasal sinuses, CT and MRI (in case the study of soft tissue formations is needed). To study the auditory analyser functions and the labyrinth state, a number of functional tests are performed including stabilometry or postulography. Audiometry is performed with electroacoustic instruments and can be subjective and objective. Impedancometry, a method of objective hearing assessment, based on measuring the acoustic resistance of a soundconducting device, is used to determine the location and nature of the auditory system disorders. All these methods help establish the correct diagnosis, clarify the localisation of the pathological process and prescribe the correct treatment.

EXCITATION OF NONLINEAR PRESSURE OSCILLATIONS IN LOW-PRESSURE FLUID FLOW USING A HIGH-PRESSURE HYDRODYNAMIC GENERATOR

The results of the study of the excitation process of nonlinear oscillations of finite amplitude pressure in a low-pressure (treated) fluid flow using a hydrodynamic oscillator of flow type, the working fluid of which has no direct contact with the fluid of the treated flow, are presented. It is shown that the oscillations from the hydrodynamic generator can be transmitted to the fluid flow through the interface (matching device) in the form of a disk with a certain acoustic resistance. It was found that resonant oscillations can be disturbed in the low-pressure flow processing chamber. The conditions of excitation of resonant oscillations in the processing chamber with a flowing liquid are found. Numerical values of the oscillation span and resonance frequencies are given.

The lung ultrasound in differential diagnostic of acute respiratory failure reason

Ultrasound lungs examination has been considered uninformative for decades due to the high acoustic resistance between soft tissues and airy lungs. Recently, the work in emergency conditions has proved the usefulness of ultrasound technologies, especially while diagnosing acute respiratory failures. Introduction of ultrasound technologies into the practice of intensive care units made it possible to change the ‘philosophy’ of diagnosing critical conditions, promoting ultrasound as primary technique, even in the era of widespread use of computed tomography. Portable ultrasound diagnostic devices, along with general clinical examination, made it possible to differentiate rapidly such acute conditions as cardiogenic shock, acute respiratory distress syndrome, pneumothorax, atelectasis, and other lung lesions