Spatially Resolved Stress Measurements in Materials With Polarisation-Sensitive Optical Coherence Tomography: Image Acquisition and Processing Aspects

Abstract:  We demonstrate that polarisation-sensitive optical coherence tomography (PS-OCT) is suitable for mapping the stress distribution within materials in a contact-free and non-destructive way. In contrast to transmission photoelasticity measurements, the samples do not have to be transparent but can be of scattering nature. Denoising and analysis of fringe patterns in single PS-OCT retardation images are demonstrated to be the bases for a quantitative whole-field evaluation of the internal stress state of samples under investigation.     

Conductivity Measurements in Dissipative Media with Electrically Short Probes

In a dissipative medium, the radio-frequency input conductance of a linear dipole, whether a bare wire or an insulated wire with its terminals short-circuited to the medium, is simply related to the conductivity of that medium provided the electrical length of the dipole is short. Model measurements were made on dipoles in saline water of known conductivity to test the theory. The feasibility of deducing conductivity of the solution by using both types of antennas as probes was demonstrated. The technique has been utilized to evaluate the electrical conductivity of rock media from measurements on probes inserted into vertical drill holes. Examples are given of measurements variously to depths of 4000 ft. In one of the cases the rock type was (fractured) granite and, in another, anorthosite. In a geophysical crustal sense, data are typical of some near-surface or sedimentary rock conditions. Since such rock media are rarely uniform in their electrical characteristics, the deduced conductivity will be a gross average conductivity of that volume of the rock approximately within the antenna region of the probe.     

Simple Scaling Relationships for Calculation of Lidar Returns from Turbid Media in Multiple Scattering Regime

Abstract

Calculations for back-scattered radiation from a turbid medium, for situations such as lidar sounding of a cloud, or in general of measurements aimed at deducing the optical properties of the medium, can involve long-time operation of computers, especially in the cases of dense media, where multiple scattering has to be considered. This paper presents some simple scaling relationships that allow the results obtained for a particular situation to be used to obtain results for situations with different optical or geometrical parameters. The effect of multiple scattering on the polarization of the returns is taken into account. Some numerical examples are presented to check these relationships. In the Appendix some details are given of the Monte Carlo code used to deal with polarization of the returns, as well as comparisons of Monte Carlo results for double scattering with the results of analytical formulas that were presented in an earlier paper.     

Phase Registration of Disturbances in Fluctuating Media Using a Spatially Separated Radio-Acoustic Generator

Measurement Techniques - Research in the field of monitoring and registration of geophysical disturbances being a complex scientific and technical problem of great importance has been carried out....     

Simulation of Sensitive Element Found on Planar Mushroom-Shaped Metamaterial for Nondestructive Testing and Searching for Inhomogeneities in Technological Media

Measurement Techniques - A computer model of a sensitive element on a planar mushroom-shaped metamaterial with Maltese cross-type cells is created. Results of a numerical experiment are presented....     

A Temperature-Controlled Device for Volumetric Measurements of Helium Adsorption in Porous Media

We describe a set-up for studying adsorption of helium in silica aerogels, where the adsorbed amount is easily and precisely controlled by varying the temperature of a gas reservoir between 80 K and 180 K. We present validation experiments and a first application to aerogels. This device is well adapted to study hysteresis, relaxation, and metastable states in the adsorption and desorption of fluids in porous media.     

Comparison between Torsional Oscillator and Ultrasonic Measurements of 4He Confined in Nano-Porous Media

We have performed torsional oscillator and ultrasonic measurements for ⁴He confined in 2D nano-porous substrate, hectorite. For ⁴He films, the resonance frequency of the torsional oscillator increases rapidly just below a superfluid transition temperature (T _C ), and then becomes constant at the lower temperature. In contrast, the sound velocity below T _C increases monotonically with decreasing temperature. For liquid ⁴He the sound velocity has a small bend at T _b of about 0.9 K. Its increase below T _b is enhanced as the pressure is increased.     

Representativeness of wind measurements with a cw Doppler lidar in the atmospheric boundary layer

The representativity problem of laser Doppler anemometer wind measurements in the boundary layer under different atmospheric conditions has been investigated theoretically and experimentally. The calculations of the mean wind-velocity measurement errors for the surface layer under different types of thermal stratification and for the boundary layer under neutral conditions have been carried out. The theoretical conclusions are confirmed by the experimental results.     

Measurements of street-crossing decision-making in pedestrians with low vision

Purpose

Crossing the street is an important but risky activity of daily living. If a pedestrian makes a poor street-crossing decision, the consequence could be serious injury or death. In order to advance our understanding of how visual and auditory information is sampled and processed to make street-crossing decisions, an accurate, reliable, and sensitive psychophysical and/or psychometric method of measurement of the street-crossing decision variable must first be developed and validated. The aim of this paper is to develop and validate a new metric for this variable.

Methods

Using a 5 point rating scale, safety ratings for eight different vehicular gap times of different durations were recorded along an unsignalized, two-lane street of one-way traffic. Safety ratings were collected from 12 normally sighted and 10 visually impaired subjects. Receiver Operating Characteristic (ROC) curves were estimated for all possible gap pairs and the discriminability (d′) of the street-crossing decision variable for all gap pairs was estimated from the area under the ROC curve.

Results

We found that our data conform with the assumptions that the underlying distributions of the decision variable are continuous, monotonic and unbounded. Using the dissimilarity matrix of d’ values for each person (which were computed for all pairings of gap times) in a one-dimensional scaling model, we estimated the means of each distribution of the decision variable relative to a center of gravity (COG) for the person. When plotting the means of the distributions against vehicular gap time, the data are best described as a non-linear function symmetric about the COG. We showed that the x-intercept (t_COG) and slope from the non-linear function can be used to assess a person's street-crossing decision-making performance for different amounts of sensory information. Using our newly developed metrics, we found no significant difference in t_COG (p = 0.30) and in the slopes of the model (p = 0.85) between normally sighted and visually impaired subjects. In addition, both subject groups centered their t_COG close to their actual crossing time.

Conclusions

A newly developed model for measuring a street-crossing decision variable functions as a valid metric that can be used to quantify street-crossing decision-making performance in pedestrians. Using this new metric, we observed that visually impaired subjects who travel independently are able to make street-crossing judgments that are comparable to those of normally sighted subjects.     

Measurements of the equivalent dose in aircraft with TLDS

For measurements of the equivalent dose of the mixed radiation fields in aircraft many different measuring devices are usually necessary for consideration of the different components of the radiation field. The possibility is discussed of using thermoluminescence dosemeters (TLDS) for determination of absorbed dose and average LET of this complex radiation field in aircraft. The HTR method, developed for determination of the equivalent dose in spacecraft, enables the measurement of the average LET in addition to the absorbed dose. Furthermore, a rem counter based on TLDs and a modified pair method (TLD-600, TLD-700) was used for determination of the absorbed dose due to the neutron component. Using small TLD crystals it is possible to obtain the depth distribution of absorbed dose and average LET by exposing TLDs in Bonner spheres with different diameters. The results indicate that the standards for determination of the effective dose may not be applicable in these mixed radiation fields in aircraft.     

Luminescent Properties of CdS Crystals Doped with Gallium and Tellurium in Cadmium Vapor

A technique is devised for vapor-phase doping CdS in the quaternary system Cd–Ga–Te–S. CdS crystals are doped with Ga and Te via four-zone annealing in a vapor phase containing Ga, Te, and Cd (the more volatile component of CdS). The luminescence spectra of the CdSGa,Te[Cd] crystals are found to contain orange and red emission bands, in contrast to those of CdS[Cd] crystals, which are dominated by green emission.     

Measurements of neutron dose rates with a balloon in Japan

Measurements of cosmic-ray neutron dose rates with a balloon in Sanriku, Japan (geographic location: 39 degrees N, 142 degrees E; corresponding geomagnetic latitude: 30 degrees N) were conducted at an altitude from 0.2 to 25 km on 25-26 August 2004 when solar activity was at an average level. Neutron dose rates given as ambient dose equivalent rates (H*(10)) were measured with high-sensitive neutron dose equivalent counters and electronic silicon personal dosimeters (EPDs). The neutron dose rates increased with increasing altitude, but they were saturated around 15-20 km and decreased with increasing altitude beyond 20 km. The neutron ambient dose equivalent rate was 1.5 microSv/h(- 1) at 20 km. Measured values were corrected for the deviation of the energy response of the dose equivalent counter from the fluence-to-ambient dose equivalent conversion coefficient, and the corrected values were very close to the calculated values with EPCARD. On the other hand, neutron measurements by the EPDs gave about 10 times overestimation because of the high sensitivity to cosmic-ray protons.     

N-B-Al共掺荧光4H-SiC施主受主对发光性能研究

施主受主共掺杂的荧光4H-SiC可以通过复合发出可见光, 影响其发光性能的一个重要因素是施主-受主掺杂的浓度。本研究通过PVT生长方法制备了3英寸N-B-Al共掺的4H-SiC晶体, 采用Raman光谱、SIMS对晶体的结晶类型和掺杂浓度进行了表征; 采用PL发射谱和激发谱、荧光衰减曲线表征和内量子效率对晶体的发光波长、强度、施主-受主对复合发光性能进行了研究。结果发现, 低浓度Al掺杂样品在室温下发出黄绿色荧光。低浓度Al掺杂在晶体中提供较少的受主; 高浓度B、N掺杂形成施主, 从而贡献充足的电子-空穴对。这些电子-空穴的复合提高了施主-受主对复合的内量子效率, 进而增强光致发光强度, 增加平均发光寿命。     

Progress in Density of States Measurements of Al Lightly Doped with Mn

Alloys of Al lightly doped with Mn are tunable superconductors, potentially useful in normal-metal/insulator/superconductor refrigerators. The superconducting transition temperature varies with Mn concentration and the density of states is like a BCS superconductor with a reduced gap. We present results from superconducting tunnel junction measurements that demonstrate the BCS-like density of states. We discuss the limitations of our measurements based upon purity of the materials used to fabricate tunnel junctions, as well as our expectations for new measurements with cleaner materials.      

Measurements of the optical properties of tissue in conjunction with photodynamic therapy

A simple optical dosimeter was used to measure the light intensity in rat liver and muscle in vivo with fibers positioned at different depths to investigate whether the light penetration changed during photodynamic therapy (PDT). The results were then correlated with measurements of the three optical-interaction coefficients μ(s), μ(a) and g for wavelengths in the range 500-800 nm for PDT-treated and nontreated rat liver and muscle tissue in vitro. Adistinct increase in the absorption coefficient was seen immediately after treatment, in agreement with the decreasing light intensity observed during the treatment, as measured with the optical dosimeter. The collimated transmittance was measured with a narrow-beam setup, and an optical integrating sphere was used to measure the diffuse reflectance and total transmittance of the samples. The corresponding optical properties were obtained by spline interpolation of Monte Carlo-simulated data. To ensure that the measured values were correct, we performed calibration easurements with suspensions of polystyrene microspheres and ink.     

Luminescence intensity monitoring in a MOS tunnel structure with inhomogeneous thickness of the insulator

The electroluminescence (EL) time series in a metal-oxide-semiconductor tunnel structure of the Al/SiO₂/p-Si type have been measured. It is demonstrated that analysis of the EL curves in some cases provides more correct information about the state of the oxide layer as compared to that obtained from the results of electric current monitoring.     

Localization of activities in the human body with a whole-body counter

The whole-body counter of the Radiation Protection Unit at the ARC Seibersdorf research GmbH has two HP Ge-detectors for measuring radionuclides, which are internally deposited in the human body. The detector system has a scanning geometry, where one detector is placed below the bed and the other detector above the bed. The body counter is placed in a massive shielded chamber. This device is especially used for measuring radioactive exposed workers with the possibility of intake by inhalation and ingestion. In the most cases whole-body counters are calibrated with anthropomorphic phantoms where activity is homogenously distributed. However, in some cases radioactivity can be located as a 'Hot Spot' in an organ. The localisation of 'Hot spots' at least in one dimension was the topic of this work. Experiments were done by means of a water-filled bottle phantom where three point sources ((137)Cs, (133)Ba and (60)Co) were placed at different positions. Measurements show that these radionuclides can be located within 1.5 cm along the longitudinal axis of the phantom with activities for (137)Cs of at least 240 Bq, (133)Ba of at least 670 Bq and (60)Co of at least 140 Bq.     

Localization in Time of Solutions for Thermoelastic Micropolar Materials with Voids

In this study we want to decide whether the decay of the solutions of the mixed initial boundary value problem in the context of thermoelasticiy of micropolar bodies with voids is sufficiently fast to guarantee that they vanish after a finite time. In fact, we prove that the effect of the micropolar structure in combination with the thermal and porous dissipation can not determine the thermomechanical deformations vanish after a finite time.