Nonlinear acoustic theory for thin porous sheets

Nonlinear method for predicting acoustic properties of thin porous sheet

Australian Species of Poecilocryptus Cameron (Ichneumonidae: Hymenoptera)

Volume: 8Start Page: 239End Page: 24

Understanding the Relationship between Perception and Production of the Beat

Impaired discrimination of sequences with a ‘beat’ in patients with Parkinson’s disease (PD) suggests the basal ganglia are responsible for the perception, or ‘internal generation’ of the beat in addition to motor timing. As a first step, we examined how young healthy participants performed on tests assessing perception, internal generation, and motor production of the beat to determine if a common mechanism guides all three processes and how this mechanism affects timing. The results suggest that perception, internal generation and production are controlled by a common timing mechanism. In general, a strong perception of the beat was associated with good synchronization accuracy (tapping and walking) and timing accuracy. Thus, previous findings of impaired beat processing in PD patients may result from deficient beat perception, in addition to or in lieu of deficient motor timing. Future studies with PD patients are needed to better understand the role of the basal ganglia in beat processing

Fluctuating pressures measured beneath a high-temperature, turbulent boundary layer on a flat plate at Mach number of 5

Fluctuating pressures were measured beneath a Mach 5, turbulent boundary layer on a flat plate with an array of piezoresistive sensors. The data were obtained with a digital signal acquisition system during a test run of 4 seconds. Data sampling rate was such that frequency analysis up to 62.5 kHz could be performed. To assess in situ frequency response of the sensors, a specially designed waveguide calibration system was employed to measure transfer functions of all sensors and related instrumentation. Pressure time histories were approximated well by a Gaussian prohibiting distribution. Pressure spectra were very repeatable over the array span of 76 mm. Total rms pressures ranged from 0.0017 to 0.0046 of the freestream dynamic pressure. Streamwise, space-time correlations exhibited expected decaying behavior of a turbulence generated pressure field. Average convection speed was 0.87 of freestream velocity. The trendless behavior with sensor separation indicated possible systematic errors

Experimental feasibility of investigating acoustic waves in Couette flow with entropy and pressure gradients

The feasibility is discussed for an experimental program for studying the behavior of acoustic wave propagation in the presence of strong gradients of pressure, temperature, and flow. Theory suggests that gradients effects can be experimentally observed as resonant frequency shifts and mode shape changes in a waveguide. A convenient experimental geometry for such experiments is the annular region between two co-rotating cylinders. Radial temperature gradients in a spinning annulus can be generated by differentially heating the two cylinders via electromagnetic induction. Radial pressure gradients can be controlled by varying the cylinder spin rates. Present technology appears adequate to construct an apparatus to allow independent control of temperature and pressure gradients. A complicating feature of a more advanced experiment, involving flow gradients, is the requirement for independently controlled cylinder spin rates. Also, the boundary condition at annulus terminations must be such that flow gradients are minimally disturbed. The design and construction of an advanced apparatus to include flow gradients will require additional technology development

Research Methods in Cognition and Emotion

In this chapter we critically survey research methods used in the field of cognition and emotion. Research on cognition and emotion addresses a great variety of topics, which include the ways in which emotional states influence cognitive processes, the role of cognition in producing emotion, and folk categories and knowledge of emotion. So great is this variety that a brief chapter cannot address all the research methods that have contributed to the expansion of knowledge that has occurred in recent years; there are too many methods, and many are relevant only to particular specialized topics. Specialized research methods are discussed throughout this volume in the chapters devoted to the relevant topics. In this chapter we restrict our attention to methodological issues that span the field of cognition and emotion, yet are in some way unique to it. Not surprisingly, these are the issues and methods that have to do with emotion itself

Comparison of measured and calculated mode redistribution associated with spinning mode transmission through circumferentially segmented lined ducts

An experiment was conducted to investigate mode redistribution in lined circular ducts with circumferential impedance nonuniformities. Mode insertion losses were measured for six-segment, two-segment, and uniform liners in a spinning mode synthesizer (SMS) in the quiet flow facility in the Langley Aircraft Noise Reduction Laboratory and correlated with predicted transmission losses. Both experiment and theory show that circumferentially segmented duct liners do scatter energy into circumferential modes of different orders. Good agreement measured and calculated attenuations was obtained for circumferential mode numbers paired with zero order radial mode numbers. For the higher order radials, the agreement was not as good

Uncertainty and Sensitivity Analyses of a Two-Parameter Impedance Prediction Model

This paper presents comparisons of predicted impedance uncertainty limits derived from Monte-Carlo-type simulations with a Two-Parameter (TP) impedance prediction model and measured impedance uncertainty limits based on multiple tests acquired in NASA Langley test rigs. These predicted and measured impedance uncertainty limits are used to evaluate the effects of simultaneous randomization of each input parameter for the impedance prediction and measurement processes. A sensitivity analysis is then used to further evaluate the TP prediction model by varying its input parameters on an individual basis. The variation imposed on the input parameters is based on measurements conducted with multiple tests in the NASA Langley normal incidence and grazing incidence impedance tubes; thus, the input parameters are assigned uncertainties commensurate with those of the measured data. These same measured data are used with the NASA Langley impedance measurement (eduction) processes to determine the corresponding measured impedance uncertainty limits, such that the predicted and measured impedance uncertainty limits (95% confidence intervals) can be compared. The measured reactance 95% confidence intervals encompass the corresponding predicted reactance confidence intervals over the frequency range of interest. The same is true for the confidence intervals of the measured and predicted resistance at near-resonance frequencies, but the predicted resistance confidence intervals are lower than the measured resistance confidence intervals (no overlap) at frequencies away from resonance. A sensitivity analysis indicates the discharge coefficient uncertainty is the major contributor to uncertainty in the predicted impedances for the perforate-over-honeycomb liner used in this study. This insight regarding the relative importance of each input parameter will be used to guide the design of experiments with test rigs currently being brought on-line at NASA Langley