scholarly journals Measurement of absorbing power of materials by the stationary wave method

1930 ◽  
Vol 127 (804) ◽  
pp. 89-110 ◽  
Keyword(s):  
Plane Waves ◽  
Stationary Wave ◽  
Small Samples ◽  
Wave System ◽  
Pressure Amplitude ◽  
Wave Method ◽  
Sound Waves ◽  
Reflected Waves ◽  
Velocity Amplitude ◽  
The Difference

The stationary wave method of determining the absorption coefficient of a material employs plane waves of sound at perpendicular incidence. It requires the use of only small samples of material and provides a rapid and convenient means of obtaining useful information. The principle of the method has been previously described, so that a brief outline is sufficient. A long pipe is provided with a source of sound at one end and is closed at the other by the test specimen. Sound waves from the source travel down the pipe and are reflected by the specimen to an extent depending on its absorbing power. The superposition of the incident and reflected waves gives rise to a stationary wave system, and the pressure amplitude varies continuously along the pipe, going through a series of maximum and minimum values. The same description applies to the velocity amplitude, with the difference that the pressure maxima coincide in position with the velocity minima and vice versa .

scholarly journals On the theory of the inertia and diffraction corrections for the Rayleigh disc

1935 ◽  
Vol 153 (878) ◽  
pp. 17-40 ◽  
Keyword(s):  
Wave Front ◽  
Acoustic Radiation ◽  
Stationary Wave ◽  
Negative Sign ◽  
Circular Disc ◽  
Sound Waves ◽  
Velocity Amplitude ◽  
Radiation Fields ◽  
Quartz Fibre

A thin circular disc suspended by a quartz fibre tends to set itself broadside on to the direction of the propagation of incident sound waves, and its use in combination with resonators is well known as a means of measuring relative intensities of acoustic radiation fields. In a progressive or stationary wave in which the velocity amplitude is │ξ│, the average couple on a circular disc of radius a is usually given by the well-known formula L͞ = - ⅔ρ 0 a 3 │ξ│ 2 sin 2α, (1) where ρ 0 is the density of the medium and α is the angle between the direction of propagation of the wave-front and the normal to the disc, while the negative sign indicates that the couple tends to diminish α.

scholarly journals Time-domain representation of ventricular-arterial coupling as a windkessel and wave system

2003 ◽  
Vol 284 (4) ◽  
pp. H1358-H1368 ◽  
Author(s):  
Jiun-Jr Wang ◽  
Aoife B. O'Brien ◽  
Nigel G. Shrive ◽  
Kim H. Parker ◽  
John V. Tyberg
Keyword(s):  
Time Domain ◽  
Aortic Pressure ◽  
Domain Model ◽  
Wave System ◽  
Reflected Waves ◽  
Arterial Hemodynamics ◽  
Arterial Model ◽  
Anesthetized Dogs ◽  
The Difference ◽  
Flow Waveforms

The differences in shape between central aortic pressure (PAo) and flow waveforms have never been explained satisfactorily in that the assumed explanation (substantial reflected waves during diastole) remains controversial. As an alternative to the widely accepted frequency-domain model of arterial hemodynamics, we propose a functional, time-domain, arterial model that combines a blood conducting system and a reservoir (i.e., Frank's hydraulic integrator, the windkessel). In 15 anesthetized dogs, we measured PAo, flows, and dimensions and calculated windkessel pressure (PWk) and volume (VWk). We found that PWk is proportional to thoracic aortic volume and that the volume of the thoracic aorta comprises 45.1 ± 2.0% (mean ± SE) of the total VWk. When we subtracted PWk from PAo, we found that the difference (excess pressure) was proportional to aortic flow, thus resolving the differences between PAo and flow waveforms and implying that reflected waves were minimal. We suggest that PAo is the instantaneous summation of a time-varying reservoir pressure (i.e., PWk) and the effects of (primarily) forward-traveling waves in this animal model.

scholarly journals The photography of airscrew sound waves

1938 ◽  
Vol 169 (937) ◽  
pp. 174-190 ◽  
Keyword(s):  
Fundamental Problem ◽  
Pressure Waves ◽  
Wave System ◽  
Pressure Amplitude ◽  
Sound Waves ◽  
Efficient Design ◽  
Wave Shape ◽  
The Past ◽  
High Speeds ◽  
Noise Production

The detail of the problem of airscrew noise has received little attention in the past, and the present research was undertaken to investigate pressure waves in the neighbourhood of an airscrew. It appears that airscrew noise may be considerably reduced by decreasing the tip speed, but the method involves an increase of airscrew- diameter which conflicts with other aspects of efficient design. The effects now considered are those due to the passage of an aerofoil through air, and the fundamental problem examined has wider application than the consideration of noise production. The primary observations are photographs of the pressure wave system caused by an airscrew blade in motion at high speeds; from the wave shape so found, and measurements of the width of the image a method is developed for estimating the pressure amplitude of the wave.

Applying the Anderson-Darling Test to Suicide Clusters

Crisis ◽  
2013 ◽  
Vol 34 (6) ◽  
pp. 434-437 ◽  
Author(s):  
Donald W. MacKenzie
Keyword(s):  
Poisson Process ◽  
Goodness Of Fit ◽  
Small Samples ◽  
Massachusetts Institute Of Technology ◽  
Homogeneous Poisson Process ◽  
Cornell University ◽  
The Difference ◽  
Suicide Clusters ◽  
Institute Of Technology ◽  
Anderson Darling

Background: Suicide clusters at Cornell University and the Massachusetts Institute of Technology (MIT) prompted popular and expert speculation of suicide contagion. However, some clustering is to be expected in any random process. Aim: This work tested whether suicide clusters at these two universities differed significantly from those expected under a homogeneous Poisson process, in which suicides occur randomly and independently of one another. Method: Suicide dates were collected for MIT and Cornell for 1990–2012. The Anderson-Darling statistic was used to test the goodness-of-fit of the intervals between suicides to distribution expected under the Poisson process. Results: Suicides at MIT were consistent with the homogeneous Poisson process, while those at Cornell showed clustering inconsistent with such a process (p = .05). Conclusions: The Anderson-Darling test provides a statistically powerful means to identify suicide clustering in small samples. Practitioners can use this method to test for clustering in relevant communities. The difference in clustering behavior between the two institutions suggests that more institutions should be studied to determine the prevalence of suicide clustering in universities and its causes.

A Dynamic Model of III-V Ternary Semiconductor Alloys in the Epitaxial Growth

1994 ◽  
Vol 340 ◽  
Author(s):  
Bing-Lin Gu ◽  
Jing-Zhi Yu ◽  
Xiao Hu ◽  
Kaoru Ohno ◽  
Yoshiyuki Kawazoe
Keyword(s):  
Dynamic Model ◽  
Ground State ◽  
Wave Method ◽  
Semiconductor Alloys ◽  
Concentration Wave ◽  
Surface Layers ◽  
Ordered Structures ◽  
Effective Interactions ◽  
Ternary Semiconductor ◽  
The Difference

ABSTRACTA concentration wave method for several interpenetrating Bravais sublattices is presented by considering the intralayer and interlayer effective interactions and the difference between the surface layers and the deeper layers in III – V alloys. The ground state ordered structures of ternary III – V semiconductor alloys are deduced and a dynamic model is established.

Nonlinear Derating of High-Intensity Therapeutic Ultrasound Beams Using Gaussian Modal Sums

2013 ◽  
Author(s):  
Seyed Ahmad Reza Dibaji ◽  
Matthew R. Myers ◽  
Joshua E. Soneson ◽  
Rupak K. Banerjee
Keyword(s):  
High Intensity ◽  
Focused Ultrasound ◽  
High Intensity Focused Ultrasound ◽  
Nonlinear Propagation ◽  
Tissue Temperature ◽  
Medical Procedure ◽  
Pressure Amplitude ◽  
Pressure Trace ◽  
The Difference ◽  
Semi Empirical

High intensity focused ultrasound (HIFU) is a noninvasive medical procedure during which a large amount of energy is deposited in a short duration which causes sudden localized rise in tissue temperature, and ultimately, cell necrosis. In assessing the influence of HIFU on biological tissue, semi-empirical mathematical models can be useful for predicting thermal effects. These models require values of the pressure amplitude in the tissue of interest, which can be difficult to obtain experimentally. One common method for estimating the pressure amplitude in tissue is to operate the HIFU transducer in water, measure the pressure amplitude, then multiply by a scaling factor that accounts for the difference in attenuation between water and tissue. This procedure can be accurate when the ultrasound amplitude is low, and the pressure trace in tissue is proportional to that in water. Because of this proportionality, the procedure for reducing the amplitude from water to tissue is called linear derating. At higher intensities, however, harmonics of the fundamental frequency are generated due to nonlinear propagation effects. Higher harmonics are attenuated differently in water and tissue (Hamilton and Blackstock [1]), and the pressure waves in water and tissue are no longer proportional to one another. Techniques for nonlinearly transforming pressure amplitudes measured in water to values appropriate for tissue are therefore desirable when bioeffects of higher intensity procedures are being studied. These techniques are labeled “nonlinear derating”.

Comparison of Sound Pressure Level of Conventional and Modified Mufflers by using CFD Analysis

2021 ◽  
Vol 8 (01) ◽  
pp. 63-67
Author(s):  
Zahoor Ullah ◽  
◽  
Hassan Ahmed ◽  
Kareem Akhtar ◽  
◽  
...  
Keyword(s):  
Sound Pressure Level ◽  
Sound Pressure ◽  
Combustion Engine ◽  
Pressure Level ◽  
Destructive Interference ◽  
Cfd Analysis ◽  
Sound Waves ◽  
Reflected Waves ◽  
Engine Cylinder ◽  
Real Challenge

The reduction of noise emitted from the exhaust of internal combustion engine is a real challenge for all automotive industries. Mufflers are designed to reflect sound waves produced by the engine in such a way to cancel the effect of each other by destructive interference between the incoming waves from engine cylinder and reflected waves from the muffler of the 2 stroke motorbike engine. Numerical simulation is carried out to study the sound pressure level (SPL) and flow variable like velocity and pressure of conventional and proposed modified reactive muffler.

Differential Scanning Calorimetry (DSC)

2008 ◽  
Author(s):  
José A. Martinho Simões ◽  
Manuel Minas da Piedade
Keyword(s):  
Differential Scanning Calorimetry ◽  
Phase Transitions ◽  
Small Samples ◽  
Calorimetric Data ◽  
Scanning Calorimetry ◽  
The Difference ◽  
Temperature Dependent Properties ◽  
Differential Scanning Calorimeters ◽  
New Applications ◽  
User Friendly

Physical and chemical changes may often be induced by raising or lowering the temperature of a substance. Typical examples are phase transitions, such as fusion, or chemical reactions, such as the solid state polymerization of sodium chloroacetate, which has an onset at 471 K: ClCH2COONa (cr) ⇋ NaCl (cr) + 1/n − (CH2COO)n − (pol) Differential scanning calorimetry (DSC) was designed to obtain the enthalpy or the internal energy of those processes and also to measure temperature-dependent properties of substances, such as the heat capacity. This is done by monitoring the change of the difference between the heat flow rate or power to a sample (S) and to a reference material (R), ΔΦ = ΦS − ΦR = (dQ/dt)S − (dQ/dt)R, as a function of time or temperature, while both S and R are subjected to a controlled temperature program. The temperature is usually increased or decreased linearly at a predetermined rate, but the apparatus can also be used isothermally. In some cases DSC experiments may provide kinetic data. According to Wunderlich, differential scanning calorimeters evolved from the differential thermal analysis (DTA) instruments built by Kurnakov at the beginning of the twentieth century. In these early DTA apparatus, the temperature difference between a sample and a reference, simultaneously heated by a single heat source, was measured as a function of time. No calorimetric data could be derived, and the instruments were used, for example, to determine the temperatures of phase transitions and to identify metals, oxides, minerals, soils, and foods. The attempts to obtain calorimetric data from DTA instruments eventually led to the development of DSC. The term differential scanning calorimetry and the acronym DSC were coined in 1963 when the first commercial instrument of this type became available. This apparatus was easy to operate, enabled fast experiments, and required only small samples (typically 5–10 mg). Its importance for materials characterization was immediately demonstrated and the DSC technique soon experienced a boom. New user-friendly commercial instruments were developed, and new applications were explored. It is, however, somewhat ironic that the method ows its still growing popularity to analytical rather than calorimetric uses.

Sound Propagation in Dilute Polyatomic Gases

1972 ◽  
Vol 27 (4) ◽  
pp. 583-592
Author(s):  
H. Moraal ◽  
F. Mccourt
Keyword(s):  
Pressure Range ◽  
Sound Propagation ◽  
Plane Waves ◽  
Point Of View ◽  
Perturbation Function ◽  
Sound Waves ◽  
Polyatomic Gas ◽  
Measured Pressure ◽  
Theory And Experiment ◽  
Good Agreement

Abstract Sound propagation in dilute pure gases, both monatomic and polyatomic, has been considered from the point of view of the Waldmann-Snider equation. It is shown that the commonly employed assumption that sound propagation in gases is equivalent to the propagation of plane waves is valid only in the region where collisions restore equilibrium faster than it is perturbed by the sound waves. A systematic truncation procedure for an expansion of the perturbation function in irreducible Cartesian tensors is introduced and then illustrated in solutions for three specific kinds of molecules, helium, nitrogen and rough spheres. The agreement between theory and experiment is rather good for sound absorption in the region where the ratio of the collision and sound frequencies is greater than 1.5. The agreement in the case of dispersion is good over the whole measured pressure range. One useful result obtained is to show the polyatomic gas calculations in second approximation have as good agreement with experiment as the calculations for noble gases in third approximation. This can be related to the possession by the polyatomic gas of a bulk viscosity which dominates in sound propagation.

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