Acoustic Analysis

Many ofthe technologies listed above can be used only with dilute suspensions. However, there are instances where particle characterization has to be performed in a concentrated phase in which dynamic processes such as aggregation, agglomeration, or flocculation may occur at a much faster rate. In other instances, such as in emulsion systems, dilution just is not feasible because the system may change due to the dilution process. The analysis of such concentrated samples is especially important in on-line processes where particles naturally exist in concentrated states. Since sound waves can travel through concentrated suspensions, ultrasonic analysis provides a mean to characterize particulate systems at concentrations up to 60% hy volume [34]. 

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This conclusion is supported by the experimental result " given by the pulsed-NMR measurement that the spin-spin relaxation time T2 is considerably shorter for the gel than that for the matrix mbber vulcanizate, which of course, indicates that the modulus is considerably higher for the gel than for the matrix mbber. More quantitatively, Maebayashi et al. measured the acoustic velocity of carbon gel by acoustic analysis and concluded that the compression modulus of the gel is about twice that of matrix mbber. Thus, at present, we can conclude that the SH layer, of course without cross-linking, is about two times harder than matrix cross-linked mbber in the filled system. 

To determine the origin of the instability frequency acoustic analysis was performed which revealed that both the quarter-wave mode of the inlet and the Helmholtz mode of the combustor-inlet system occurred at 35 Hz. The phase... 

To determine the dominant frequency of excitation, the near-field acoustic spectrum was obtained using a microphone. Typical near-field acoustic spectra for an excited jet and a natural jet are shown and compared in Fig. 29.5. When multiple peaks were observed in the spectrum, the peak with the highest spectral amplitude was denoted as the excitation frequency. By systematically varying the dimensions of the cavity, flow excitation occurred over a wide range of frequencies (4-40 kHz). Table 29.2 summarizes the normalized data. Initial tests were performed with semi-annular cavities to eliminate possible pressure mismatching associated with flow ejection effect in fully annular cavities. The semi-annular cavities in this case were flush mounted at the nozzle exit (x = L) to simplify the acoustic analysis. 

C. Martin, L. Benoit, Y. Sommerer, F. Nicoud, and T. Poinsot. Les and acoustic analysis of combustion instability in a staged turbulent swirled combustor. AIAA Journal, 44(4) 741-750, 2006. 

S. Roux, G. Lartigue, T. Poinsot, U. Meier, and C. Berat. Studies of mean and unsteady flow in a swirled combustor using experiments, acoustic analysis and large eddy simulations. Combust. Flame, 141 40-54, 2005. 

Acoustic analysis is done in three steps 1) determination of source strength, 2) calculation of sound pressure levels throughout the primary coolant system, and 3) calculation of random vibration response of components and structures. 

Le Troedec et al. [39] treated hemp fibers with sodium hydroxide solution 1.6 M pH 14 for 48 h at 20 C, in order to increase adhesion properties between natural fibers and cement matrix, increasing durabihty of the material. After treatment with NaOH, fibers were washed with distilled water with 1 v/v% of acetic add, imtil reaching neutral pH. Results revealed that fiber treatment increased the maximal resistance of composite material by 60% with respect to composite material elaborated with natural fibers without treatment. Additionally, it was confirmed through acoustic analysis that natural fiber treatment delayed the start of damage mechanisms of fiber-matrix interface caused by degradation of natural cellulosic fibers. 

Dexamethasone was injected into the Reinke space under local anaesthesia via the operating channel of a transnasal flexible lar mgoscope in an office setting. Treatment outcomes were measured before, 1 month after, and 3 months after the injection, using videolaryngostroboscopy (VLS), maxima phonation time (MPT), 10-item voice handicap index (VHI-10), acoustic analysis and perceptual evaluation. VLS examination at 3-months posttreatment demonstrated that vocal lesions of 10 and 19 patients were resolved or reduced, respectively. Objective measurements showed increased MPT and decreased VHI-10. 

Even in Europe, acoustic analysis of cicada species has led to the discovery of new and important information about the biogeography of the Cicadetta species (Sueur and Puissant, 2007)... 

Acoustic analysis detects changes in the properties of acoustic waves as they travel at ultrasonic frequencies in piezoelectric materials. The interaction between the waves and the phase-matter composition facilitates chemical selectivity and, thus, the detection of CWA s. These are commonly known as surface acoustic wave (SAW) sensors. Reported studies indicate detection limits as low as 0.01 mg m for organophosphorus analytes within a 2 min analysis [1]. There are several commercially available SAW instruments, which can automatically monitor for trace levels of toxic vapors from G-nerve agents and other CWAs, with a high degree of selectivity. A major advantage of SAW detectors is that they can be made small, portable and provide a real-time analysis of unknown samples. One of the drawbacks of these instruments is that sensitivity and a rapid response time are inversely related. In an ideal instrument, both parameters would be obtained without sacrificing one for the other. 

In vibration and acoustic analysis the viscoelastic spectrum are often represented as a master curve known as the reduced frequency nomograph. Figure 14.3 is an example of a nomograph constructed with simulated data. In addition to the thermomechanical information that is usually presented, both absolute temperature and frequency axes are included in the nomograph. The information presented by the inclusion of the temperature and frequency axes is already contained in the master curve of the viscoelastic data. However, it is convoluted within the master curve. In order to obtain frequency data at other tanperatures, a new master curve must be created from the raw data or transformed from the original master curve. 

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