Single-photon compressive imaging with some performance benefits over raster scanning

A single-photon imaging system based on compressed sensing has been developed to image objects under ultra-low illumination. With this system, we have successfully realized imaging at the single-photon level with a single-pixel avalanche photodiode without point-by-point raster scanning. From analysis of the signal-to-noise ratio in the measurement we find that our system has much higher sensitivity than conventional ones based on point-by-point raster scanning, while the measurement time is also reduced.     

Investigation of the synergy in intumescent polyurethane by 3D computed tomography

The morphology of carbonized materials resulting from an intumescence phenomenon was studied. The investigated material is a polyurethane matrix filled either by 30 wt.-% of ammonium polyphosphate or by a combination of 28 wt.-% of ammonium polyphosphate and 2 wt.-% of nano-magnesium oxide. These fillers were incorporated in the polyurethane directly during the synthesis step. The carbonized materials or char, are obtained in a specific fire scenario. Characterization of their morphology is carried out using X-ray computed tomography. The heat conductivity of the systems is additionally measured as a function of temperature in order to correlate structure and properties of the intumescent residues. The formation of different char structures with incorporation of magnesium oxide (in particular formation of bubbles of different size) is first evidenced. These observations are consistent with the heat conductivity data. Tomography images demonstrate that the intumescence process is a dynamic process since non degraded polymer is left at the beginning of the fire test, which is not the case for longer time. The dispersion of fillers has finally been investigated in the chars and it is evidenced different steps of intumescence's development in the material.     

The Progression of the Impurities Injected into the Plasma Following by Soft X-ray Arrays on HL-2A Tokamak

Small amounts of metallic impurity is injected by laser blow-off on HL-2A tokamak in order to study transport phenomena. The particle transport is interpretated along     

Quantitative measurement of solids distribution in gas–solid riser flows using electrical impedance tomography and gamma densitometry tomography

An electrical impedance tomography (EIT) system has been developed to non-invasively measure particle distributions in the riser of a pilot-scale circulating fluidized bed (CFB). Although EIT systems have often been applied to yield qualitative information about gas–solid flows, the present EIT system yields quantitative information that is validated by comparison to a gamma densitometry tomography (GDT) system. EIT and GDT were applied to the CFB riser (14-cm inner diameter, 5.77-m height) containing fluid catalytic cracking particles in air. The flows examined were annular with a dilute core and had average and near-wall solids volume fractions up to 0.25 and 0.66, respectively. For all cases, the average and near-wall solids volume fractions from EIT and GDT agreed to within 0.03 and 0.07, respectively. This good agreement suggests that, where feasible, EIT can be used in place of GDT, which is advantageous since EIT systems are often safer, less expensive, and faster than GDT systems.     

Continuum reconstruction of the pore scale microstructure for Fontainebleau sandstone

A stochastic geometrical modeling technique is used to reconstruct a laboratory scale Fontainebleau sandstone with a sidelength of 1.5 cm. The model reconstruction is based on crystallite properties and diagenetic parameters determined from two-dimensional images. The three-dimensional pore scale microstructure of the sandstone is represented by a list of quartz crystallites defined geometrically and placed in the continuum. This allows generation of synthetic μ-CT images of the rock model at arbitrary resolutions. Quantitative microstructure comparison based on Minkowski functionals, two-point correlation function and local porosity theory indicates that this modeling technique can provide more realistic and accurate models of sandstones than many existing techniques used currently. Synthetic μ-CT images at different resolutions from a laboratory scale model of Fontainebleau sandstone are made available to the scientific community for resolution dependent petrophysical analysis.     

Quantitative visualization of high-speed 3D turbulent flow structures using holographic interferometric tomography

Using holographic interferometry the three-dimensional structure of unsteady and large-scale motions within subsonic and transonic turbulent jet flows has been studied. The instantaneous 3D flow structure is obtained by tomographic reconstruction techniques from quantitative phase maps recorded using a rapid-switching, double reference beam, double pulse laser system. The reconstruction of the jets studied here reveal a three-dimensional nature of the flow. In particular an increasing complexity can be seen in the turbulence as the flow progresses from the jet nozzle. Furthermore, a coherent three-dimensional, possibly rotating, structure can be seen to exist within these jets. The type of flow features illustrated here are not just of fundamental importance for understanding the behavior of free jet flows, but are also common to a number of industrial applications, ranging from the combustion flow within an IC engine to the transonic flow through the stages of a gas turbine.     

Tomography Methods for Vector Field Study Using Space-Distributed Fiber Optic Sensors with Integral Sensitivity

The problem of tomographic reconstruction of vector physical fields is studied. This problem can be solved by using fiber optic measuring lines (MLs) of special shape. In the case that the ML output signal is proportional to the vector's projection, the ML must be shaped like a narrow loop. This problem can be solved by means of the integral theorem. If an ML output signal is proportional to projection of a vector derivative with respect to ML direction, the ML with a step shape can be used. In this case the potential component of a vector field can be reconstructed. This approach can be applied to research on distributions of electromagnetic, deforming, and other vector fields and can be used for developing systems to monitor vector physical fields.     

Tomographic reconstruction of volume emission coefficients from line integral data

The technique of reconstructive tomography (RT) is a powerful method of obtaining local, spatially resolved volumetric emission coefficients from line integral data. The applicability of this technique as a diagnostic for nonuniform sources is studied using simulated data with and without noise. The major advantage of RT techniques is that they may be applied, without restriction, to highly asymmetric data as well as symmetric data. When applied to symmetric data, the technique appears to be less susceptible to noise than Abel inversion techniques. Also examined is a method of accounting for self-absorption under certain circumstances.     

Measurement of the decay lengths of the near-field signal in tapping mode

In near-field optics, the use of vertical vibration of the probe is of great interest in order to prevent the tip crash, in tapping mode. The optical signal is often obtained through a lock-in amplifier using a feedback on this vertical vibration. Therefore, harmonics of the optical signal are available. The reconstruction of the near-field signal, from these harmonics, enables the knowledge of the vertical variations of the near-field signal, without the use of the slower technique of approach curves or the use of photocounter. In this work, we use this reconstruction to measure the vertical decay lengths of the near-field data with the Prony’s and the simplex methods. We compare both methods and we discuss the results in terms of filtering by the lock-in.