(1998). Human cognitive abilities: A survey of factor analytic studies. Gifted and Talented International: Vol. 13, No. 2, pp. 97-98.

Human cognitive abilities: A survey of factor analytic studies

Human Development Report, 1990.@@@Human Development Report, 1991.

るもので、もっとも普遍的なのは目撃の有無。 ・ Jakobson (1957:147) : a verbal category ‘which takes into account three events ― a narrated event, a speech, and a narrated speech event’. ・ Boas (1938:133) : ‘while for us definiteness, number, and time are obligatory aspects, we find in another language location near the speaker or somewhere else, source of information ― whether see, heard, or inferred ― as obligatory aspects’.

Evidentiality(證據性)をめぐって

Round jets originating from a pipe nozzle are computed by large-eddy simulations (LES) to investigate the effects of the nozzle-exit conditions on the flow and sound fields of initially laminar jets. The jets are at Mach number 0.9 and Reynolds number 105, and exhibit exit boundary layers characterized by Blasius velocity profiles, maximum root-mean-square (r.m.s.) axial velocity fluctuations between 0.2 and 1.9% of the jet velocity, and momentum thicknesses varying from 0.003 to 0.023 times the jet radius. The far-field noise is determined from the LES data on a cylindrical surface by solving the acoustic equations. Jets with a thinner boundary layer develop earlier but at a slower rate, yielding longer potential cores and lower centreline turbulent intensities. Adding random pressure disturbances of low magnitude in the nozzle also increases the potential core length and reduces peak r.m.s. radial velocity fluctuations in the shear layer. In all the jets, the shear-layer transition is dominated by vortex rolling-ups and pairings, which generate strong additional acoustic components, but also amplify the downstream-dominant low-frequency noise component when the exit boundary layer is thick. The introduction of inlet noise however results in weaker pairings, thus spectacularly reducing their contributions to the sound field. This high sensitivity to the initial conditions is in good agreement with experimental observations.

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Influence of nozzle-exit boundary-layer conditions on the flow and acoustic fields of initially laminar jets

Why peer discussion improves student performance on in-class concept questions

The effects of microjets on the aerodynamic characteristics of a Mach 09 high-Reynolds axisymmetric jet are investigated and are interpreted in the light of previous acoustic results These measurements are obtained by means of Stereoscopic Particle Image Velocimetry in planes normal to the jet axis Three parameters of the microjets system are varied: the outgoing mass flux per microjet, the number of microjets and their layout in the azimuth of the main jet The aerodynamic results indicate a strong correlation between the maximum level of turbulence just behind the nozzle exit and the high-frequency noise, previously shown to potentially balance the acoustic benefits obtained for lower frequencies The maximum level of turbulence measured at the longitudinal position corresponding to half the potential core length is also highly correlated to the jet noise reduction, which is highlighted by the similar evolution of these two quantities regarding the mass flux per microjet and the number of microjets For low values of the number of microjets, the microjets are shown to act independently, and their contributions to the turbulence reduction are retrieved far downstream the impinging point without any noticeable azimuthal diffusion

/pdf/jet-noise-reduction-by-impinging-microjets-an-acoustic-1zi48bznbm.pdf

Jet-Noise Reduction by Impinging Microjets : An Acoustic Investigation Testing Microjet Parameters

The effect of screech tones on the broadband shock-associated noise of underexpanded jets is investigated experimentally. Screech is removed by means of a notched nozzle, and the properties of the broadband shock-associated noise in the screech-free configuration are compared to that in a screeching flow. It is first demonstrated that the suppressing technique used is nonintrusive in that it does not alter the shock-cell structure of the jet plume. It is then shown that screech has an effect on the aerodynamics of the jet, which induces changes in the broadband shock-associated noise. Indeed, screech accelerates the damping of the shock-cell pattern, leading to an attenuation of the broadband shock-associated noise and a shifting of this noise component to higher frequencies. Moreover, a tuning between the peak frequency of the broadband shock-associated noise and the screech frequency is observed. It is also deduced from the directivity of the broadband shock-associated noise in the far field that the co...

/pdf/broadband-shock-associated-noise-in-screeching-and-non-20wvcf0hx6.pdf

Broadband shock-associated noise in screeching and non-screeching underexpanded supersonic jets

An experimental investigation of pressure fluctuations generated by a single-stream compressible jet is carried out in an anechoic wind tunnel. Measurements are performed using a linear array of microphones installed in the near region of the jet and a polar arc of microphones in the far field. The main focus of the paper is on the analysis of the pressure fluctuations in the near field. Three novel signal processing techniques are presented to provide the decomposition of the near-field pressure into hydrodynamic and acoustic components. The procedures are all based on the application of the wavelet transform to the measured pressure data and possess the distinctive property of requiring a very simple arrangement to obtain the desired results (one or two microphones at most). The hydrodynamic and acoustic pressures are characterized separately in terms of their spectral and statistical quantities and a direct link between the acoustic pressure extracted from the near field and the actual noise in the far field is established. The analysis of the separated pressure components sheds light on the nearly Gaussian nature/intermittent behaviour of the acoustic/hydrodynamic pressure. The higher sensitivity of the acoustic component to the Mach number variation has been highlighted as well as the different propagation velocities of the two pressure components. The achieved outcomes are validated through the application to the same data of existing separation procedures evidencing the advantages and limitations of the new methods.

Wavelet decomposition of hydrodynamic and acoustic pressures in the near field of the jet

Near-field acoustic measurements and time-resolved schlieren visualisations are performed on 10 round jets with the aim of analysing the different parts of the feedback loop related to the screech phenomenon in a systematic fashion. The ideally expanded Mach number of the studied jets ranges from to . The single source of screech acoustic waves is found at the fourth shock tip for A1 and A2 modes, and at either the third or the fourth shock tip for the B mode, depending on the Mach number. The phase of the screech cycle is measured throughout schlieren visualisations in the shear layer from the nozzle to the source. Estimates of the convective velocities are deduced for each case, and a trend for the convective velocity to grow with the axial distance is pointed out. These results are used together with source localisation deduced from a two-microphone survey to determine the number of screech periods contained in a screech loop. For the A1 and B modes, four periods are contained in a loop for cases in which the radiating shock is the fourth, and three periods when the radiating shock tip is the third, whereas the loop of the A2 mode contains five periods.

Thomas Castelain

Papers

Jet-Noise Reduction by Impinging Microjets : An Acoustic Investigation Testing Microjet Parameters

Broadband shock-associated noise in screeching and non-screeching underexpanded supersonic jets

Wavelet decomposition of hydrodynamic and acoustic pressures in the near field of the jet

Experimental characterisation of the screech feedback loop in underexpanded round jets

The boss is always right: Preschoolers endorse the testimony of a dominant over that of a subordinate