Reference Spot Research Articles

Thermal compensation of monolithic distributed fibre optic sensors: From the lab to the field

Distributed fibre optic sensing (DFOS) is gaining popularity as a diagnostic solution for short-term non-destructive testing (NDT) and long-term structural health monitoring (SHM). However, there are still challenges to be overcome, particularly with regard to long-term measurements under real field conditions, taking into account, among other things, temperature changes. These changes affect strain measurements through both thermal expansion and optical effects, and appropriate correction depends on the internal design of the sensor and the installation methods. Therefore, despite the fact that thermal compensation is one of the key prerequisites for correct data interpretation, there are no universal and clear procedures for DFOS. The lack of sufficient guidelines and proven applications is the main motivation for undertaking studies. The scope and novelty of the presented research lies in 1) the theoretical explanation of the thermal performance of monolithic DFOS sensors compared to the layered sensing cables; 2) the analysis and correction of strain data measured with monolithic sensors placed in a thermal chamber; 3) the verification of the laboratory results and the proposed approach in real field conditions: in a concrete footbridge deck and in a steel underground gas pipeline. All presented measurements were performed with high spatial resolution (mm order) Rayleigh-based interrogators under the control of conventional reference spot thermistors. The research demonstrated the linear thermal response of the monolithic sensors and confirmed their usefulness for distinguishing between length- and stress-dependent strains. Finally, the thermal compensation approach was proposed and verified in real operating conditions.

Analysisof Beam Walk in Inter-Satellite Laser Link: Implications for Differential Wavefront Sensing in Gravitational Wave Detection

Achieving space-based gravitational wave detection requires the establishment of an interferometer constellation. It is necessary to establish and maintain stable laser interferometric links using the differential wavefront sensing (DWS) technnique. When the distant measurement beam experiences pointing jitter, it causes beam walk on the surface of the local detector. The reduced overlap between the local reference spot and the distant spot increases the nonlinear errors in the DWS technique, which need to be suppressed. Numerical analysis was conducted on the spatial beam interference signals of the DWS technique when the distant measurement beam experienced pointing jitter. An experimental measurement system was designed, and the beam walk was suppressed using a conjugate imaging system. The results show that within a range of 300 μrad, the optical path with the imaging system can reduce measurement errors by at least 83%. This way also helps to reduce pointing jitter noise in inter-satellite links, thereby improving laser pointing control accuracy.This method would provide a valuable reference for future DWS measurement systems.

Method for testing freeform surfaces based on a Shack-Hartmann sensor with plane wavefront scanning and stitching.

Currently, the surface error measurement technology for freeform faces a significant contradiction between measurement accuracy and dynamic range. The study proposes a non-null testing method for measuring freeform surfaces by utilizing a Shack-Hartmann wavefront sensor to emit a small aperture parallel beam and scan along the normal direction at the center of subapertures for stitching (SHPSS). A mathematical model based on ray tracing and the reflection theorem is established to calculate the sampling points on an ideal freeform surface, the reference spot array on CCD, and the corresponding relationship between microlens array and spots. An algorithm is proposed to iteratively calculate the wavefront aberration and gradually approach the actual sampling points using the established model. Theoretical analysis and numerical simulation results indicate that SHPSS can increase the dynamic range and improve the accuracy of wavefront reconstruction. The error analysis of the SHPSS method is carried out, the measurement accuracy of full aperture freeform surface is 11.45 nm. A testing system is set up and experiments are conducted on a 100 mm aperture freeform reflective mirror. The RMS of the SHPSS test results is less than λ/30 (λ=635 nm) compared to the interferometric test results. By analyzing five groups of repeated measurement experiments, the repeatability accuracy of SHPSS method is less than 1/80 λ (RMS). This demonstrates the feasibility and measurement capabilities of the method for freeform surface testing.

Critical analysis of in-plane free-space light beam coupling using photonic curved micromirrors

Free-space coupling of Gaussian light beams using flat and curved photonic microelectromechanical systems mirrors was analyzed in detail. The theoretical background and the non-ideal effects, such as limited micromirror extent, asymmetry in the curvature of spherical micromirrors, misaligned axes, and micromirror surface irregularities, were analyzed. The derived formulas were used to study and compare theoretically and experimentally the behavior of flat (one-dimensional), cylindrical (two-dimensional), and spherical (three-dimensional) micromirrors. The analysis focused on the regime of dimensions in which the curved micromirrors radius of curvature is comparable to the incident beam Rayleigh range, also corresponding to a reference spot size. A transfer matrix-based field and power coupling coefficients were derived for general micro-optical systems accounting for different matrix parameters in the tangential and sagittal planes of the microsystem taking into account the possible non-idealities. The results were presented in terms of normalized quantities such that the findings are general and can be applied to different situations. In addition, silicon micromirrors were fabricated with controlled shapes and used to experimentally analyze the coupling efficiency at the visible and near-infrared wavelengths.

XPS and FTIR investigations of the transient photocatalytic decomposition of surface carbon contaminants from anatase TiO2 in UHV starved water/oxygen environments

This paper explores the transient photocatalytic oxidation mechanism of carbon contaminants from a high surface area anatase TiO2 pellet under starved water/oxygen reaction conditions created when specimens are irradiated via a 375 nm UV laser inside the UHV analysis chamber of an XPS spectrometer. Complementary results are also provided following similar UV irradiations and reaction procedures in an evacuated in situ reaction cell of a Fourier-transform infrared spectrometer (FTIR). An interactive and non-steady state transient photocatalytic reaction is observed between surface carbon species and strongly adsorbed H2O brought to the exterior surface of the pellet via UV photodesorption from within the deeper lying pores of the pellet. The reaction stoichiometry and quantum efficiency of the reaction are reported at various irradiation intensities. In situ FTIR spectral features are also presented and discussed for a non-UV treated TiO2 sample and a 2-hour UV-treated TiO2 sample under evacuated conditions also showing the decomposition of carbon contaminants species and the consumption of adsorbed water/hydroxyls with the ensuing formation of carboxyl (HO-CO) carbon species and isolated surface hydroxyls. The photocatalytic decomposition of carbon species and the concomitant consumption of oxygen containing species was also tracked by following the XPS spectral changes of a UV-irradiated area on the pellet surface compared to a dark reference spot on the same specimen. Eight different reaction cases at four different UV intensities, repeated twice each, were also investigated using separate pieces of the same TiO2 media. The measured stoichiometry for the decomposition of carbon species and consumption of oxygen ranged from 0.53 during the first 10–20 min of irradiation and increased to 0.65 with an average value of 0.59 and a standard deviation of 0.11. These data suggest that the reaction product and leaving group from the TiO2 surface is primarily CO2 during the first 10–20 min of initial reaction with perhaps a small fraction of CO toward the end of reaction. Heating the sample specimen to 100 °C for 2-hour inside the XPS-UHV analysis chamber prior to UV illumination was effective in eliminating photocatalytic oxidation and carbon removal from the surface thereby demonstrating that strongly adsorbed water (prior to heating in vacuum) was a critical and limiting reagent in the overall H2O transport and reaction process.Photon efficiencies for the reaction were calculated based on the number of carbon species removed from the XPS-observable surface versus the number of the UV photons adsorbed in the topmost 2 nm of the sample. The highest photon efficiency observed was 0.0186 after 5–10 min of UV exposure at 1.5 mW/cm2. All reaction cases showed a significant efficiency drop after 30 min of UV irradiation due to the consumption of the adsorbed reactants, both carbon and water. From detailed deconvolution of the XPS C 1s spectra, UV irradiation showed a high selectivity towards hydrocarbon contaminant decomposition, which was 75% ± 5% of all carbon species removed.

Distributed Fibre Optic Sensing (DFOS) for Deformation Assessment of Composite Collectors and Pipelines.

Due to the low costs of distributed optical fibre sensors (DFOS) and the possibility of their direct integration within layered composite members, DFOS technology has considerable potential in structural health monitoring of linear underground infrastructures. Often, it is challenging to truly simulate the actual ground conditions at all construction stages. Thus, reliable measurements are required to adjust the model and verify theoretical calculations. The article presents a new approach to monitor displacements and strains in Glass Fiber Reinforced Polymer (GFRP) collectors and pipelines using DFOS. The research verifies the effectiveness of the proposed monitoring solution for health monitoring of composite pipelines. Optical fibres were installed over the circumference of a composite tubular pipe, both on the internal and external surfaces, while loaded externally. Analysis of strain profiles allowed for calculating the actual displacements (shape) of the pipe within its cross-section plane using the Trapezoidal method. The accuracy of proposed approach was positively verified both with reference spot displacement transducer as well as numerical simulations using finite element method (FEM). DFOS could obtain a comprehensive view of structural deformations, including both strains and displacements under externally applied load. The knowledge gained during research will be ultimately used for renovating existing collectors.

Traceable calibration of Shack–Hartmann wavefront sensors employing spherical wavefronts

Traceable, highly accurate calibration of wavefront sensors such as Shack–Hartmann sensors is a challenging task and an active field of research. We have developed a measurement system for the traceable calibration of wavefront sensors employing spherical wavefronts and a point light source in combination with a three-axis linear stage. We obtain an absolute calibration of sensor errors, including the reference spot position and wavefront gradient-dependent errors for each microlens individually. We discuss the main error influences and present an initial measurement uncertainty budget for the calibration. The calibration can be performed with an expanded measurement uncertainty (95% coverage interval) of better than 5 μrad for the wavefront gradient deviation.

One-Year Clinical Outcomes following Implantation of InnovaTM Self-Expanding Nitinol Stents in Patients with Peripheral Artery Diseases Presenting Femoropopliteal Artery Lesions.

Aim: Although the Innova™ self-expanding nitinol stent (Boston Scientific, Marlborough, MA) exhibits acceptable performance in long-term safety and efficacy when used for the treatment of femoropopliteal (FP) lesions, clinical outcomes following its implantation have not been systematically studied in real-world settings. We investigated the one-year clinical outcomes after implantation of Innova™ self-expanding nitinol stents for the treatment of FP lesions in real-world settings.Methods: In this multicenter study, 481 lesions in 453 consecutive patients with peripheral artery disease (PAD) (74 ± 9 years; male, 70%; diabetes mellitus, 61%; dialysis, 27%; critical limb ischemia, 37%) who underwent endovascular therapy with the implantation of Innova™ self-expanding nitinol stents for FP lesions were analyzed from February 2016 to April 2017. The primary endpoint was one-year restenosis, whereas the secondary endpoints included one-year major adverse limb events and predictors for one-year restenosis.Results: The mean lesion length was 18 ± 10 cm. One-year restenosis and major adverse limb event rates were 36% and 18%, respectively. Multivariate analysis revealed that the presence of diabetes mellitus (odds ratio [OR]: 1.83; 95% confidence interval [CI]: 1.07–3.13), distal reference vessel diameter (OR: 1.86; 95% CI: 1.09–3.16), spot stenting (OR: 2.27; 95% CI: 1.27–4.06), and lack of one-year cilostazol treatment (OR: 0.58; 95% CI: 0.33–1.00) were independent risk factors for one-year restenosis.Conclusion: The current study demonstrated one-year clinical outcomes after Innova™ self-expanding nitinol stent placement for the treatment of FP lesions, including challenging cases in real-world settings.

A Probabilistic Approach for Maximizing Travel Journey WiFi Coverage Using Mobile Crowdsourced Services

A public transport journey planning service often yields multiple alternative journeys plans to get from a source to a destination. In addition to journey preferences, such as connecting time and walking distance, passengers can select the optimal plan based on mobile crowdsourced WiFi coverage available along the journey. This requires discovering mobile crowdsourced WiFi services available along the journey path. However, this task is challenging due to the uncertain availability of discovered services. To enhance the availability of WiFi coverage, we propose a probabilistic approach to discover groups of available crowdsourced WiFi services along with the journey segments. We first analyze the log of their trajectories and use a density estimation technique to discover reference spots representing the frequently visited locations. Then, a joint discrete Fourier transform and autocorrelation analysis are applied to mine the periods of the presence of moving crowdsourced services with respect to each reference spot. A low-complexity cluster analysis based on Jensen–Shannon divergence is then used to mine the periodic movement behaviors of services during the identified periods. Finally, mobile crowdsourced WiFi services that are simultaneously available at intersecting reference spots are grouped. The QoS of discovered groups is computed in terms of availability confidence, failover capacity, aggregated bandwidth capacity, and coverage. Additionally, we propose an algorithm to determine the best public transport journey plan offering based on the QoS of available WiFi service groups along the journey path. We conduct a comprehensive comparative study to validate the effectiveness of the proposed framework.

Museo Nacional Amazónico: una deuda pendiente

The Amazonian National Museum was intended to be a public cultural space in the region and a reference spot for the knowledge and understanding of the Amazonia, the natural resources, geography, and cultural expressions specific to each Amazonian community, their history and cities. The museum promoted the research, conservation, education, exhibition and dissemination of tangible and intangible, natural and cultural heritage in their original context. It was designed as an institution of national level and international relevance. This cultural space was devoted to the great natural and cultural richness and diversity of the Peruvian Amazonia. The collection comprised archeological, historic, natural, ethnographic, artistic, photographic, documentary items, among others. All of them would be subject to preventive preservation measures, both organic and non-organic, and would be included in a preservation and restoration program for all kind of pieces. Another aspect of particular relevance was the generation of a strong bond with the educational institutions under an intercultural and pedagogical approach, so that the Museum could be a supporting resource for the teacher during the educational process. The programs should be structured and aligned with the curriculum design of the educational institution so as to facilitate formal learning, with the exhibition being the canal to reinforce or support the knowledge gained in class.

Hierarchical trajectory clustering for spatio-temporal periodic pattern mining

Spatio-temporal periodic pattern mining is to find temporal regularities for interesting places. Many real world spatio-temporal phenomena present sequential and hierarchical nature. However, traditional spatio-temporal periodic pattern mining ignores the consideration of sequence, and fails to take into account inherent hierarchy. This paper proposes a hierarchical trajectory clustering based periodic pattern mining that overcomes the two common drawbacks from traditional approaches: hierarchical reference spots and consideration of sequence. We propose a new trajectory clustering algorithm which considers semantic spatio-temporal information such as direction, speed and time based on Traclus and present comparative experimental results with three popular clustering methods: Kernel function, Grid-based, and Traclus. We further extend the proposed trajectory clustering to hierarchical clustering with the use of the single linkage approach to generate a hierarchy of reference spots. Experimental results reveal various hierarchical periodic patterns, and demonstrate that our algorithm outperforms traditional reference spot detection algorithms.

A continuous scale-space method for the automated placement of spot heights on maps

Spot heights and soundings explicitly indicate terrain elevation on cartographic maps. Cartographers have developed design principles for the manual selection, placement, labeling, and generalization of spot height locations, but these processes are work-intensive and expensive. Finding an algorithmic criterion that matches the cartographers’ judgment in ranking the significance of features on a terrain is a difficult endeavor. This article proposes a method for the automated selection of spot heights locations representing natural features such as peaks, saddles and depressions. A lifespan of critical points in a continuous scale-space model is employed as the main measure of the importance of features, and an algorithm and a data structure for its computation are described. We also introduce a method for the comparison of algorithmically computed spot height locations with manually produced reference compilations. The new method is compared with two known techniques from the literature. Results show spot height locations that are closer to reference spot heights produced manually by swisstopo cartographers, compared to previous techniques. The introduced method can be applied to elevation models for the creation of topographic and bathymetric maps. It also ranks the importance of extracted spot height locations, which allows for a variation in the size of symbols and labels according to the significance of represented features. The importance ranking could also be useful for adjusting spot height density of zoomable maps in real time.

Study of Stability of Precise Tiled-grating Device

To satisfy the high-stability requirement of a tiled grating, we have analyzed and optimized the stability of a newly designed precise tiledgrating device considering three aspects: structure design, transmission chain, and control algorithms. The main structure of the device is changed from a parallel-board structure to a new tetrahedral brace design, enhancing the overall vibration stability; during the analysis of the transmission chain, the adjustment accuracy and stability of the device were ensured by slowing the growth of the error transmission factor; and for the optimization analysis of the PID control algorithms, we adopted a latch compensation method to avoid the saturated loss and a four-point central difference method to avoid the disturbances, thus enhancing the stability control of the device. To test the stability of the device, an optical experiment with a reference spot was designed. The experimental results showed that over 380 s, the ambient excitation response was always within an acceptable range. The average deflections about the X axis and Y axis are 0.243 and 0.00146 μrad, respectively, which satisfy the stability requirement.

Spinal Near-Infrared Spectroscopy Measurements During and After Thoracoabdominal Aortic Aneurysm Repair: A Pilot Study

Near-infrared spectroscopy (NIRS) is a noninvasive technique that allows continuous monitoring of regional hemoglobin oxygen saturation (rSo2). We evaluated its application to survey oxygenation of the spinal cord region during open thoracoabdominal aortic aneurysm (TAAA) repair and postoperatively in the intensive care unit (ICU). We also validated its association with motor-evoked potential (MEP) monitoring during the operation. The rSo2 curves of 15 patients (8 men; mean age, 64.2 ± 7.7 years) were measured continuously with NIRS at spinal cord levels of the thoracic vertebrae T3 (optode 1, reference spot) and T12 (optode 2) during open TAAA repair. T12/T3 ratios were calculated. NIRS measurements were continued in the intensive care unit and stopped 24 hours after the operation. MEP monitoring was performed in all patients during the procedure. No clinical signs of spinal cord ischemia were documented in any of the patients. Continuous NIRS measurements were successfully performed in all patients during and after the operation. T12/T3 ratios were significantly lower in the MEP ratios that were less than 50% compared with the MEP ratios that were 50% or higher (p= 0.037). NIRS is an easily applicable noninvasive tool for continuous surveillance of oxygenation of the spinal cord region during TAAA repair and postoperatively in the intensive care unit. The rSo2 curves provide useful information concerning hemodynamic changes in oxygenation of the spinal cord region and might contribute to early detection of spinal cord ischemia. Further investigation is needed before broad clinical implementation.

In vivo measurements of regional hemoglobin oxygen saturation values and limb-to-arm ratios of near-infrared spectroscopy for tissue oxygenation monitoring of lower extremities in healthy subjects.

ObjectiveNear-infrared spectroscopy (NIRS) is a noninvasive technique that allows monitoring of regional hemoglobin oxygen saturation (rSO2) values and might have a role in the diagnosis of peripheral arterial disease. We assessed the reproducibility and inter-subject variability of rSO2 values and rSO2 limb-to-arm ratios (LARs) in lower extremities of healthy subjects.MethodsThe rSO2 values and rSO2 LARs were calculated in eight healthy subjects without peripheral arterial disease. The rSO2 values were measured at rest at six fixed spots at each lower limb and a reference spot at each upper arm. NIRS provided the rSO2 values without involvement of any other processing technique. After measurements were completed, rSO2 LARs were calculated by dividing the rSO2 value of a lower extremity spot by the rSO2 value of the arm. Measurements were performed twice on 1 day and repeated on 4 different days.ResultsMean coefficients of variation of measurements of rSO2 values and rSO2 LARs at the same spot in the same subject were respectively less than 6% and 8% for every measurement spot over time. Coefficients of variation of measurements at the same spot between different subjects were less than 15% and 19% for every measurement spot respectively.ConclusionNIRS is an easily applicable, noninvasive tool for measurement of tissue oxygenation of lower extremities in healthy subjects. The reproducibility of rSO2 values and rSO2 LARs at the same measurement spot in the same subject is good.

Multiple Protein Analysis of Formalin-fixed and Paraffin-embedded Tissue Samples with Reverse phase Protein Arrays

Reverse-phase protein arrays (RPPAs) have become an important tool for the sensitive and high-throughput detection of proteins from minute amounts of lysates from cell lines and cryopreserved tissue. The current standard method for tissue preservation in almost all hospitals worldwide is formalin fixation and paraffin embedding, and it would be highly desirable if RPPA could also be applied to formalin-fixed and paraffin embedded (FFPE) tissue. We investigated whether the analysis of FFPE tissue lysates with RPPA would result in biologically meaningful data in two independent studies. In the first study on breast cancer samples, we assessed whether a human epidermal growth factor receptor (HER) 2 score based on immunohistochemistry (IHC) could be reproduced with RPPA. The results showed very good concordance between the IHC and RPPA classifications of HER2 expression. In the second study, we profiled FFPE tumor specimens from patients with adenocarcinoma and squamous cell carcinoma in order to find new markers for differentiating these two subtypes of non-small cell lung cancer. p21-activated kinase 2 could be identified as a new differentiation marker for squamous cell carcinoma. Overall, the results demonstrate the technical feasibility and the merits of RPPA for protein expression profiling in FFPE tissue lysates.

Offline estimation of 2 D crystal lattice parameters by processing the electron diffraction image

Electron diffraction provides useful information about the internal composition of materials and has been in the use of material scientists for more than fifty years. In order to extract useful information from offline diffraction images, they are manually analyzed by using some photometric technique. Manual analysis is however a cumbersome, laborious and difficult task. To reduce the labors of material scientists one can employ image processing techniques to perform automated analysis, due to the well established popularity and clear evidence of widely used image processing techniques. In this work an image processing technique is being proposed for the extraction of 2D unit cell information from diffraction images on one hand and finding the 2D point group contained by the lattices on the other. The technique employs a morphological shrinking operation to find the center of each spot in the underlying preprocessed diffraction image. This is followed by the extraction of eight points with reference to the spot produced by the transmitted electron beam. The resultant nine points, i.e. the extracted eight plus the reference spot generated by the transmitted electron beam, are then subjected to symmetry operations, rotation symmetry and mirror symmetry, in polar coordinate system, to classify the point group of the lattice produced by the electron diffraction. One of the difficult task, even in manual analysis, is to ascertain the exact spot where the transmitted electron beam hit the sample at the time of realization of the image. This has been accurately and intuitively done by employing the notion that the transmitted spot must have greater number of pixels, with the highest gray value, among the diffracted spots. The proposed strategy has been applied to a sample set of various images and the results shows that the technique is efficient in determining the unit cell in 2D and classify the point group with good accuracy.

Mining periodic behaviors of object movements for animal and biological sustainability studies

Periodicity is one of the most frequently occurring phenomena for moving objects. Animals usually have periodic movement behaviors, such as daily foraging behaviors or yearly migration behaviors. Such periodic behaviors are the keys to understand animal movement and they also reflect the seasonal, climate, or environmental changes of the ecosystem. However, periodic behaviors could be complicated, involving multiple interleaving periods, partial time span, and spatiotemporal noises and outliers. In this paper, we address the problem of mining periodic behaviors for moving objects. It involves two sub-problems: how to detect the periods in complex movements, and how to mine periodic behaviors. A period is usually a single value, such as 24 h. And a periodic behavior is a statistical description of the periodic movement for one specific period. For example, we could describe an animal's daily behavior in the way that "From 6 pm to 6 am, it has 90% probability staying at location A and from 7 am to 5 pm, it has 70% probability staying at location B and 30% probability staying at location C". So our tasks is to first detect the periods and then describe each periodic behavior according to different periods. Our main assumption is that the observed movement is generated from multiple interleaved periodic behaviors associated with certain reference locations. Based on this assumption, we propose a two-stage algorithm, Periodica, to solve the problem. At the first stage, the notion of reference spot is proposed to capture the reference locations. Through reference spots, multiple periods in the movement can be retrieved using a method that combines Fourier transform and autocorrelation. At the second stage, a probabilistic model is proposed to characterize the periodic behaviors. For a specific period, periodic behaviors are statistically generalized from partial movement sequences through hierarchical clustering. Finally, we show two extensions to the Periodica algorithm: (1) missing data interpolation, and (2) future movement prediction. Empirical studies on both synthetic and real data sets demonstrate the effectiveness of the proposed method.

Shack-Hartmann 센서를 이용한 파면측정의 정확도 향상에 관한 연구

Shack-Hartmann 파면측정 센서는 적응광학 분야에서 파면측정용으로 가장 널리 사용되고 있다. Shack-Hartmann 센서에서 파면측정 알고리즘은 크게 점영상의 중심점 탐색 알고리즘과 파면복원 알고리즘으로 나눌 수 있다. 이 중 점영상의 중심점 탐색은 파면측정 결과에 크게 영향을 미치나 많은 연구결과에도 불구하고 최적의 중심점 측정 알고리즘 및 내부 변수 설정에 대한 일반적인 해결책은 아직 제시되지 못하고 있다. 현재, 중심점 탐색 알고리즘으로는 무게중심법(center of gravity)이 가장 널리 사용되고 있다. 본 연구에서는 중심점 탐색 알고리즘에 의한 측정 정확도 분석을 위해 무게중심법과 상관관계법(correlation)을 함께 고려하였다. 이를 위해 Shack-Hartmann 센서의 파면측정 과정을 전산모사하였고, 이로부터 중심점 탐색 알고리즘과 관련하여 무게중심법 및 상관관계법에서의 노이즈 특성을 비교, 분석하였다. 또한, 무게중심법에서 문턱값(threshold value)의 설정에 따른 파면측정의 정확도에 대한 분석을 통하여 노이즈 제거를 위한 최적의 문턱값을 제안하였다. 이와 더불어 Shack-Hartmann 센서 시스템을 구성하여 디포커스(defocus)를 발생시키고 이를 측정하는 실험을 수행함으로써 파면측정 알고리즘 및 전산모사 결과를 검증하였다. The SharkHartmann wavefront sensors are the most popular devices to measure wavefront in the field of adaptive optics. The Shack-Hartmann sensors measure the centroids of spot irradiance distribution formed by each corresponding micro-lens. The centroids are linearly proportional to the local mean slopes of the wavefront defined within the corresponding sub-aperture. The wavefront is then reconstructed from the evaluated local mean slopes. The uncertainty of the Shack-Hartmann sensor is caused by various factors including the detector noise, the limited size of the detector, the magnitude and profile of spot irradiance distribution, etc. This paper investigates the noise propagation in two major centroid evaluation algorithms through computer simulation; 1st order moments of the irradiance algorithms i.e. center of gravity algorithm, and correlation algorithm. First, the center of gravity algorithm is shown to have relatively large dependence on the magnitudes of noises and the shape & size of irradiance sidelobes, whose effects are also shown to be minimized by optimal thresholding. Second, the correlation algorithm is shown to be robust over those effects, while its measurement accuracy is vulnerable to the size variation of the reference spot. The investigation is finally confirmed by experimental measurements of defocus wavefront aberrations using a Shack-Hartmann sensor using those two algorithms.

222Rn Emission Flux and Soil-Atmosphere Interface: Comparative Analysis of Different Measurement Techniques

Abstract Radon emission flux at the ground-atmosphere interface is one of the measurements commonly made for environmental purposes and on prospective mining sites. There are a number of ways of making such measurements. Generally an 'accumulation' technique is used. This method consists in determining the radon activity at a given time, inside a container placed on the ground with one side open, facing downward. The radon activity is determined by sampling the air inside the confinement system with a scintillation flask. The purpose of this work was to simplify this method by using other radon activity measurement techniques. The flux measurements made by the usual method, used as reference (spot sampling), were compared with those made using a silicon detector (continuous measurement) and with a solid trace detector (integrated measurement). For the latter two methods, a correction factor is applied to obtain the real value of the 222Rn emission flux yielded by the reference method.