Bulk viscosity of gauge theory plasma at strong coupling

This paper provides a review of the development of profiling oceanographic lidars. These can provide quantitative profiles of the optical properties of the water column to depths of 20 to 30 m in productive coastal waters and to depths of 100 m for a blue lidar in the open ocean. The properties that can be measured include beam attenuation, diffuse attenuation, absorption, volume scattering at the scattering angle of 180 deg, and total backscattering. Lidar can be used to infer the relative vertical distributions of fish, plankton, bubbles, and other scattering particles. Using scattering as a tracer, lidar can provide information on the dynamics of the upper ocean, including mixed-layer depth, internal waves, and turbulence. Information in the polarization of the lidar return has been critical to the success of many of these investigations. Future progress in the field is likely through a better understanding of the variability of the lidar ratio and the application of high-spectral-resolution lidar to the ocean. Somewhat farther into the future, capabilities are likely to include lidar profiling of temperature in the ocean and an oceanographic lidar in space.

https://www.spiedigitallibrary.org/journals/optical-engineering/volume-53/issue-5/051405/Review-of-profiling-oceanographic-lidar/10.1117/1.OE.53.5.051405.pdf

Review of profiling oceanographic lidar

Despite its fundamental role in the dynamics of compressible fluids, bulk viscosity has received little experimental attention and there remains a paucity of measured data. Acoustic spectroscopy provides a robust and accurate approach to measuring this parameter. Working from the Navier-Stokes model of a compressible fluid one can show that the bulk viscosity makes a significant and measurable contribution to the frequency-squared acoustic attenuation. Here we employ this methodology to determine the bulk viscosity of Millipore water over a temperature range of 7 to 50 degrees Celsius. The measured attenuation spectra are consistent with the theoretical predictions, while the bulk viscosity of water is found to be approximately three times larger than its shear counterpart, reinforcing its significance in acoustic propagation. Moreover, our results demonstrate that this technique can be readily and generally applied to fluids to accurately determine their temperature dependent bulk viscosities.

Temperature dependence of bulk viscosity in water using acoustic spectroscopy

Despite its fundamental role in the dynamics of compressible fluids, bulk viscosity has received little experimental attention and there remains a paucity of measured data. Acoustic spectroscopy provides a robust and accurate approach to measuring this parameter. Working from the Navier-Stokes model of a compressible fluid one can show that the bulk viscosity makes a significant and measurable contribution to the frequency-squared acoustic attenuation. Here we employ this methodology to determine the bulk viscosity of Millipore water over a temperature range of 7 to 50?C. The measured attenuation spectra are consistent with the theoretical predictions, while the bulk viscosity of water is found to be approximately three times larger than its shear counterpart, reinforcing its significance in acoustic propagation. Moreover, our results demonstrate that this technique can be readily and generally applied to fluids to accurately determine their temperature dependent bulk viscosities.

/pdf/temperature-dependence-of-bulk-viscosity-in-water-using-3hupe4w6uz.pdf

Two-dimensional stimulated Brillouin scattering microscopy is demonstrated for the first time using low power continuous-wave lasers tunable around 780 nm. Spontaneous Brillouin spectroscopy has much potential for probing viscoelastic properties remotely and non-invasively on a microscopic scale. Nonlinear Brillouin scattering spectroscopy and microscopy may provide a way to tremendously accelerate the data aquisition and improve spatial resolution. This general imaging setup can be easily adapted for specific applications in biology and material science. The low power and optical wavelengths in the water transparency window used in this setup provide a powerful bioimaging technique for probing the mechanical properties of hard and soft tissue.

/pdf/stimulated-brillouin-scattering-microscopic-imaging-azqpscqge6.pdf

Stimulated Brillouin Scattering Microscopic Imaging.

The aim is to develop a rapid and direct method for measuring the bulk viscosity of a liquid as a function of temperature. Brillouin scattering of a laser beam in fresh water and salt water at different temperatures has been studied. The results show that there exists a close temperature-dependent relationship among the Brillouin frequency shift, the Brillouin linewidth, and the bulk viscosity of water. Thus the bulk viscosity of water can be determined directly from Brillouin-scattering measurements. The method has a high signal-to-noise ratio and high accuracy.

Measurement of the bulk viscosity of liquid by Brillouin scattering

Measurements of sound speed in the water by Brillouin scattering using pulsed Nd:YAG laser

A new approach to remote sensing of the ocean is proposed. It is based on a combination of Brillouin scattering, incoherent lidar techniques and high-resolution frequency discrimination via gas absorption cells. The results of theoretical and experimental research are given. This approach provides the capability of rapid real-time monitoring of sound-speed or temperature profiles both in the open ocean and in littoral zones with high resolution and high accuracy.

The edge technique as used in Brillouin lidar for remote sensing of the ocean

The signal estimate and statistical uncertainty in the measurements of Brillouin shift by the edge technique are analyzed in detail. A signal to noise parameter factor is introduced and is used to discuss the statistical uncertainty in the measurements. The effect of signal averaging and the effect due to background noise are analyzed. Some helpful conclusions are predicted.

Analyzing statistical errors for measurements of Brillouin scattering by the edge technique

In this paper, the use of the time-domain scattering matrix for ultrasonic characterization of defects is explored. An approach based on convolutional sparse coding is proposed for extraction of the shift-invariant features of the time-domain scattering matrix. The results of a simulation show that the proposed approach can be reliably used for classification of the rough cracks. In addition, the mean sizing error and its standard deviation are also reduced compared with the use of the frequency domain scattering matrix. In experiments, a 1.5 mm slot and 1.5 mm elliptical defect were sized to within 0.25 mm using a 2.5 MHz, 64 element linear array with an element pitch of 0.5 mm. Excellent sizing results were obtained for inclined slots with a large orientation angle (i.e. 60°). 

Jianfeng Xu

Papers

Measurement of the bulk viscosity of liquid by Brillouin scattering

Measurements of sound speed in the water by Brillouin scattering using pulsed Nd:YAG laser

The edge technique as used in Brillouin lidar for remote sensing of the ocean

Analyzing statistical errors for measurements of Brillouin scattering by the edge technique

Ultrasonic defect characterization using time-domain scattering matrices and convolutional sparse coding