The Life of a New York City Noise Sensor Network.

Noise pollution is one of the topmost quality of life issues for urban residents in the United States. Continued exposure to high levels of noise has proven effects on health, including acute effects such as sleep disruption, and long-term effects such as hypertension, heart disease, and hearing loss. To investigate and ultimately aid in the mitigation of urban noise, a network of 55 sensor nodes has been deployed across New York City for over two years, collecting sound pressure level (SPL) and audio data.

Phase singularity diffusion.

We follow the trajectories of phase singularities at nulls of intensity in the speckle pattern of waves transmitted through random media as the frequency of the incident radiation is scanned in microwave experiments and numerical simulations. Phase singularities are observed to diffuse with a linear increase of the square displacement 〈R2〉 with frequency shift. The product of the diffusion coefficient of phase singularities in the transmitted speckle pattern and the photon diffusion coefficient through the random medium is proportional to the square of the effective sample length.

Mesoscopic speckle.

We have measured first and second order statistics of the velocity of phase singularities v in evolving speckle patterns of microwave radiation transmitted through random quasi-1D samples as the frequency is swept and relate these to global statistics of speckle evolution. When v is normalized by the standard deviation of the fractional intensity change, the probability distribution and correlation function of v approach those for random Gaussian fields even for localized waves. Analogous results are found for transmitted intensity normalized by the total transmission.

Observation of singularities in multiply scattered microwave fields.

Speckle patterns of arbitrary resolution are obtained by applying the sampling theorem to measurements of two orthogonal components of the microwave field transmitted through multiply scattering samples. Core structures of phase singularities, phase critical points, and polarization singularities are explored. We find that equiphase lines connect phase singularities with opposite topological signs except for the bifurcation lines, which run through a phase saddle point, in agreement with predictions by Freund [Phys.