Foveal vision predictively sensitizes to defining features of eye movement targets

Despite the fovea's singular importance for active human vision, the impact of large eye movements on foveal processing remains elusive. Building on findings from passive fixation tasks, we hypothesized that during the preparation of rapid eye movements (saccades), foveal processing anticipates soon-to-be fixated visual features. Using a dynamic large-field noise paradigm, we indeed demonstrate that sensitivity for defining features of a saccade target is enhanced in the pre-saccadic center of gaze. Enhancement manifested in higher Hit Rates for foveal probes with target-congruent orientation, and a sensitization to incidental, target-like orientation information in foveally presented noise. Enhancement was spatially confined to the center of gaze and its immediate vicinity. We suggest a crucial contribution of foveal processing to trans-saccadic visual continuity which has previously been overlooked: Foveal processing of saccade targets commences before the movement is executed and thereby enables a seamless transition once the center of gaze reaches the target.

Nil-potent vacuum in homodyne noise

In the absence of a signal field, vacuum entering through the empty beam splitter port is considered to be the sole contributor to the output noise of conventional two-port homodyne detection. We study a modified configuration that alters the input coefficient of vacuum, predicting an output noise less than that of the conventional configuration. Measurements, however, reveal identical output noise profiles for both the configurations. We explain the observations in terms of the incident field noise alone, and suggest that vacuum does not contribute to homodyne noise or shot-noise. We extend our results to the measurement of squeezed light, with non-ideal detectors.

Experimental investigation of NACA-0012 airfoil instability noise with sawtooth trailing edges

This study presents an experimental study of the effect of sawtooth trailing-edge serrations on airfoil instability noise. The far-field noise measurements are obtained to investigate the noise radiation characteristics of a NACA-0012 airfoil operated at various angles of attack: 0°, 5°, and 10°, and covered Reynolds numbers of 2.87 × 105, 3.71 × 105, and 5 × 105. It is found that as the Reynolds number increases, the instability noise shifts from tonal to broadband, whereas as the angle of attack increases, it shifts from broadband to tonal. Furthermore, sawtooth trailing-edges are used to minimize instability tonal noise, leading to considerable self-noise reduction. Parametric studies of the serration amplitude 2 h and streamwise wavelength λ are performed to understand the effect of sawtooth trailing-edges on noise reduction. It is observed that the sound pressure reduction level is sensitive to both the amplitude and streamwise wavelength. Overall, the sawtooth trailing-edge with larger amplitude and smaller wavelength produce the greatest amount of noise reduction.

Influence of the hypermagnetic field noise on the baryon asymmetry generation in the symmetric phase of the early universe

We study a matter turbulence caused by strong random hypermagnetic fields (HMFs) that influence the baryon asymmetry evolution due to the Abelian anomalies in the symmetric phase in the early Universe. Such a matter turbulence is stipulated by the presence of the advection term in the induction equation for which a fluid velocity is dominated by the Lorentz force in the Navier–Stokes equation. For random HMFs, having nonzero mean squared strengths, we calculate the spectra for the HMF energy and the HMF helicity densities. The latter function governs the evolution of the fermion asymmetries in the symmetric phase before the electroweak phase transition (EWPT). In the simplest model based on the first SM generation for the lepton asymmetries of $$e_\mathrm {R,L}$$ e R , L and $$\nu _{e_\mathrm {L}}$$ ν e L , we calculate a decline of all fermion asymmetries including the baryon asymmetry, given by the ‘t Hooft conservation law, when one accounts for a turbulence of HMFs during the universe cooling down to EWPT. We obtain that the stronger the mean squared strength of random initial HMFs is, the deeper the fermion asymmetries decrease, compared to the case in the absence of any turbulence.

An experimental investigation of turbulent flow over a two-dimensional obstacle on a flat plate

Aeroacoustic and aerodynamic characteristics of the turbulent boundary layer encountering a large obstacle are experimentally investigated in this paper. Two-dimensional obstacles with a square and a semi-circular cross-section mounted on a flat plate are studied in wind tunnel tests, with particular interests in the shear layer characteristics, wall pressure fluctuations, and far-field noise induced by the obstacles. Synchronized measurements of the far-field noise and the wall pressure fluctuations were conducted using microphone arrays in the far-field and flush-mounted in the plate, respectively. Additionally, the streamwise and wall-normal velocity fluctuations behind the obstacle were measured using the X-wire probe. The measured velocity profiles, spectra, and wall pressure spectra are compared, showing that the rectangular obstacle has a significant impact on both the turbulent flow and far-field noise. The large-scale vortical structures shed from the obstacles can be identified in the wall pressure spectra, the streamwise velocity spectra, and the wall pressure coherence analysis. Within the shear layer, the pairing of vortices occurs and the frequency of the broadband peak in the velocity spectra decreases as the shear layer grows downstream. Further eddy convective velocities of large-scale vortical structures inside the shear layer were analyzed based on the wall pressure fluctuations.

Optimal design of multi-blade centrifugal fan based on partial coherence analysis

Considering that there are many design variables in multi-blade centrifugal fans, the complicated design parameters and internal flow uncertainty increase the difficulty of studying fan noise mechanisms. This study adopted the impact noise between the airflow at the impeller outlet inside the fan and the volute tongue as the research object. Based on the influence of mutual interfering noise sources on the system noise, a partial coherence function was introduced to establish a system noise model. The correlation between the static pressure of the impeller outlet in the volute tongue area of the centrifugal fan and far-field noise of the fan was analyzed and obtained. The peak values of fundamental frequency and average sound pressure level of a far-field noise receiving points were selected as the optimization goals, taking the volute tongue placement angle θ1, volute tongue radius R, and center distance L1 as the optimization objects. The Latin hypercube sampling was used to select 35 groups of sampling points and a Kriging agent model was established. The NSGA-II genetic algorithm was used to optimize the volute tongue profile. The results showed that the flow rate was increased by 1.2 m3/min, the far field noise of the centrifugal fan was reduced by 1.9 dB, while the fan efficiency increased by 3%, static pressure increased by 27 Pa, and peak values of fundamental frequency reduced by 8%.