We investigate the phase sensitivity of the fundamental mode of hollow-core photonic bandgap fibers to strain and acoustic pressure. A theoretical model is constructed to analyze the effect of axial strain and acoustic pressure on the effective refractive index of the fundamental mode. Simulation shows that, for the commercial HC-1550-02 fiber, the contribution of mode-index variation to the ov...

acoustic experimental data of irib (islamic republic of iran broadcasting) server room was taken to measure the acoustic noise characteristics of frequency and sound pressure level (spl). the purposes of this paper are measuring the noise pollution and its evaluation through the regulations. the measurements were taken in two stages. the first one was taken at 10 points by sound investigator 22...

The maximum value of acoustic pressure within an ultrasonic beam is limited by acoustic saturation. The t oretical basis for acoustic saturation has been analyzed previously. In this work, a high-power pulse source is used to drive acoustic pressure levels from an ultrasonic beam to saturation. An automatic procedure determines the field’s beam axis using a calibrated Marconi PVDF hydrophone. T...

An acoustic prediction capability for supersonic axisymmetric jets was developed on the basis of OVERFLOW Navier-Stokes CFD (Computational Fluid Dynamics) code of NASA Langley Research Center. Reynolds-averaged turbulent stresses in the flow fie ld are modeled with the aid of Spalart-Alimaras one-equation turbulence modeL Appropriate acoustic and outflow boundary conditions were implemented to ...

Directing acoustic waves along curved paths is critical for applications such as ultrasound imaging, surgery and acoustic cloaking. Metamaterials can direct waves by spatially varying the material properties through which the wave propagates. However, this approach is not always feasible, particularly for acoustic applications. Here we demonstrate the generation of acoustic bottle beams in homo...

Three perforate-over-honeycomb liner configurations, one uniform and two with spanwise variable impedance, are evaluated based on tests conducted in the NASA Grazing Flow Impedance Tube (GFIT) with a plane-wave source. Although the GFIT is only 2” wide, spanwise impedance variability clearly affects the measured acoustic pressure field, such that three-dimensional (3D) propagation codes are req...

In this paper we derive a general expression for the acoustic Casimir pressure between two parallel slabs made of arbitrary materials and whose acoustic reflection coefficients are not equal. The formalism is based on the calculation of the local density of modes using a Green’s function approach. The results for the Casimir acoustic pressure are generalized to a sphere/plate configuration usin...

Previous optical studies have shown threshold behavior of single-contrast agent microbubbles. Below the acoustic pressure threshold, phospholipid-coated microbubbles with sizes <5.0 mum in diameter oscillate significantly less than above the threshold pressure. Previous studies also revealed an acoustic pressure-dependent attenuation of ultrasound by microbubble contrast agents. In this study, ...

During high-frequency oscillatory ventilation (HFOV), the primary variable affecting lung volume is the mean airway pressure (MAP). To effectively maintain lung recruitment and optimal gas exchange without overstretching (or collapsing) the lung, MAP should be set between the lower and upper inflection points of the pressure-volume curve of the lung. At present, there is no efficacious means th...

The acoustic behaviour of wind instruments is largely determined by their acoustic impedance spectrum measured at the embouchure or 'input' to the instrument. The acoustic impedance Z is the ratio of acoustic pressure p U and its extrema identify the frequencies of resonances and antiresonances due to standing waves in the bore. (For example see [1].) Backus [2] reports measurements of the acou...