Influence of sampling on three-dimensional surface shape measurement

In order to accurately measure an object’s three-dimensional surface shape,the influence of sampling on it was studied.First,on the basis of deriving spectra expressions through the Fourier transform,the generation of CCD pixels was analyzed,and its expression was given.Then,based on the discrete expression of deformation fringes obtained after sampling,its Fourier spectrum expression was derived,resulting in an infinitely repeated"spectra island"in the frequency domain.Finally,on the basis of using a low-pass filter to remove high-order harmonic components and retaining only one fundamental frequency component,the inverse Fourier transform was used to reconstruct the signal strength.A method of reducing the sampling interval,i.e.,reducing the number of sampling points per fringe,was proposed to increase the ratio between the sampling frequency and the fundamental frequency of the grating.This was done to reconstruct the object’s surface shape more accurately under the condition of m>4.The basic principle was verified through simulation and experiment.In the simulation,the sampling intervals were 8 pixels,4 pixels,2 pixels,and 1 pixel,the maximum absolute error values obtained in the last three situations were 88.80%,38.38%,and 31.50%in the first situation,respectively,and the corresponding average absolute error values are 71.84%,43.27%,and 32.26%.It is demonstrated that the smaller the sampling interval,the better the recovery effect.Taking the same four sampling intervals in the experiment as in the simulation can also lead to the same conclusions.The simulated and experimental results show that reducing the sampling interval can improve the accuracy of object surface shape measurement and achieve better reconstruction results.

Agricultural Contamination of the Surface Waters of the Upper Ouémé in Benin: The Case of Heavy Metals and Pesticides

Objective: The main objective of this study was to assess the degree of contamination of surface waters by heavy metals and pesticides. Method: To this end, data were collected in December 2022 from four specific sampling stations: Okpara, Térou, Affon and Adjiro. Levels of heavy metals, including cadmium, chromium, copper, iron, mercury, nickel and lead, were measured and subjected to in-depth statistical analysis using graphical summation models. In addition, the concentrations of pesticide active ingredients present in the samples were interpreted and evaluated. The statistical data collected during this study were processed using R software, version 3.5.0. Results: The values obtained at the different stations Okpara, Térou, Affon and Adjiro are respectively Arsenic (2 × 10-4 mg/L;2.2 × 10-1 mg/L;1.2 × 10-4 mg/L;2 × 10-4 mg/L), Cadmium (4.4 × 10-5 mg/L;1.1 × 10-2 mg/L;10-4 mg/L;4 × 10-4 mg/L). Then Copper (7 × 10-4 mg/L;3 × 10-3 mg/L;7 × 10-4 mg/L;1 × 10-4 mg/L), Iron (1.51 mg/L;6.4 × 10-1 mg/L;2.0012 mg/L;2.9 × 10-1 mg/L), Lead (0 mg/L;0 mg/L;1.5 × 10-3 mg/L;1.5 × 10-3 mg/L). Mercury, nickel and chromium were not detected in surface waters. It is important to note that the values obtained for trace metals (Cadmium, Chromium, Copper, Iron, Mercury, nickel and chromium were not detected in surface waters. It is important to note that the values obtained for trace metals (cadmium, chromium, copper, iron, mercury, nickel and lead) were all below the guideline standards set by the WHO in 2006 for uncontaminated surface waters. This indicates that the surface waters of the Upper Ouémé were below acceptable contamination thresholds in terms of heavy metals. However, the presence of pesticide active ingredients such as cyfluthrin, endosulfan-alpha, endosulfan-beta, profenosfos, tihan, atrazine, gala super and glycel clearly indicates that these surface waters are subject to agricultural contamination.

Surface form inspection with contact coordinate measurement:a review

Parts with high-quality freeform surfaces have been widely used in industries,which require strict quality control during the manufacturing process.Among all the industrial inspection methods,contact measurement with coordinate measuring machines or computer numerical control machine tool is a fundamental technique due to its high accuracy,robustness,and universality.In this paper,the existing research in the contact measurement field is systematically reviewed.First,different configurations of the measuring machines are introduced in detail,which may have influence on the corresponding sampling and inspection path generation criteria.Then,the entire inspection pipeline is divided into two stages,namely the pre-inspection and post-inspection stages.The typical methods of each sub-stage are systematically overviewed and classified,including sampling,accessibility analysis,inspection path generation,probe tip radius compensation,surface reconstruction,and uncertainty analysis.Apart from those classical research,the applications of the emerging deep learning technique in some specific tasks of measurement are introduced.Furthermore,some potential and promising trends are provided for future investigation.

Field trial measurement and channel modeling for reconfigurable intelligent surface

With the advantage of programmable electromagnetic properties,Reconfigurable Intelligent Surfaces(RISs)havedrawn wide attention from both industry and academia.RIS-assisted communication systems can promote hugewireless channel quality improvement and remarkable coverage enhancement.This paper proposes generalpathloss model,radiation pattern and mirror beam effect of 1-bit RIS at sub-6 GHz band.Field trails have beencarried out in outdoor and indoor deployment scenarios.The proposed model is validated through extensivesimulations and field-trial measurements.In addition,an optimized RIS phase-shit design process for the mirrorbeam elimination is proposed and validated with simulations.The proposed theoretical model and measurementresults can promote future research and application in RIS-assisted communications.

A new method for position-sensitive measurement of beta surface contamination

In this paper, we propose a new method for position-sensitive measurement of beta surface contamination. With a position-sensitive detector of enlarged sensitive detection area, accurate information of the contamination distribution can be obtained. The positionsensitive detection is based on a large-area plastic scintillator and the wavelength shifting(WLS) fibers and adopts the ‘‘light center of gravity'' method. Optical transmission of the detector is simulated with a preliminary detector model, and feasibility of the detector design and measurement method is evaluated using an experiment system.The simulation and experiment results at different beta-ray incident points on the scintillator surface show that there is a polynomial relationship between the average amplitude ratio of the output pulses from the two parallel WLS fibers in the same fiber layer and the relative distance from the incident point to the WLS fiber.

Surface shape detection methods for large radio telescopes

The surface accuracy of a radio telescope is directly related to its operational efficiency and detection sensitivity.This is crucial under high-frequency observation conditions,where surface shape errors need to be controlled to within 1/16 of the working wavelength.In addition,the primary reflector of large radio telescopes is subject to dynamic deformation,caused by factors such as gravity and thermal effects.This paper presents a method for detecting the surface shape of radio telescopes using radio interferometry techniques combined with active reflector adjustment technology.This enables accurate assessment and correction of surface errors,ensuring the electrical performance of the radio telescope.This study investigates the practical applications of high-precision measurement techniques,such as microwave holography,out-of-focus holography,and wavefront distortion methods at the Tianma 65 m radio telescope(TMRT).Furthermore,the study presents the construction method of gravity models at different elevation angles and demonstrates the efficacy of the active reflector model.The results of the measurements indicate that the application of these methods to the TMRT has led to a notable enhancement of the accuracy of the primary reflector and a substantial improvement in efficiency in the Q-band.Through a process of iterative measurements and adjustments,the surface shape error is ultimately reduced to 0.28 mm root mean square(RMS).

STUDY OF NON-CONTACT MEASUREMENT OF FREE-FORM SURFACES

A non contact three dimensional measurement method is presented in this paper.This system consists of a laser triangulation probe,a probe head and a coordinate measuring machine (CMM).The measurement principle of the system is discussed,and a system calibration method employing a reference ball is proposed.The geometric model involving four frames is established to calculate the data points based on the reading of the laser probe and position information from the CMM.A measuring experiment for gesso free form surface using this system is carried out.

NON-CONTACT MEASUREMENT OF SCULPTURED SURFACE OF ROTATION

A method for measuring the sculptured surface of rotation by using coordinatemeasuring machine (CMM) and rotary table is proposed. The measurement is realized during thecontinuous rotation of the workpiece mounted on the rotary table while the probe moves along thegeneratrix of the surface step by step. This method possesses lots of advantages such as simplicityof probe motion, high reliability and efficiency. Some key techniques including calibration of theeffective radius of the probing system, determination of the position of axis of rotation,auto-centering of the workpiece, data processing algorithm, are discussed. Approaches fordetermining the coordinates on measured surface, establishing workpiece coordinate system andsurface fitting are presented in detail. The method can be used with contact or non-contact probes.Some fragile ceramic and plaster parts are measured by using the system consisting of a CMM, rotarytable, motorized head and non-contact laser triangulation probe. The measuring uncertainty is about0.02 mm which meets the general requirement in most cases.

Surface seasonal mass changes and vertical crustal deformation in North China from GPS and GRACE measurements

The Earth is an elastic body,and the surface mass loading changes will lead to elastic loading deformation on the surface of the Earth.In this study,we investigated the surface seasonal mass changes and vertical crustal deformation in North China using the data obtained by the techniques of the Global Positioning System(GPS),Gravity Recovery and Climate Experiment(GRACE)and Surface Loading Models(SLMs).The seasonal annual signal and semi-annual signal obtained by the three techniques show strong correlations.The average value of the weighted root-mean-square(WRMS)of the all 30 sites is 58%after deducting the GRACE-obtained vertical deformation from the GPS-derived vertical deformation.However,the consistency of results between GPS and SLMs is not so good,with a 31%mean WRMS reduction,due to the fact that the global SLMs perform not well in North China.The GRACEmeasured long-term trend is deducted from the GPS-obtained vertical rates to reveal the crustal displacement caused by the underground factors such as tectonic movement and groundwater in North China.The results show that the rates of stations HECX and TJBH are very large,more than 10 mm/yr,which suggests that the surface subsidence is caused by excessive exploitation of groundwater.

NON-CONTACT MEASUREMENT SYSTEM OF FREEFORM SURFACE AND NURBS RECONSTRUCTION OF MEASUREMENT POINTS

Based on the development of the non-contact measurement system of free-formsurface, NURBS reconstruction of measurement points of freeform surface is effectively realized bymodifying the objective function and recursive procedure and calculating the optimum number ofcontrol points. The reconstruction precision is evaluated through Ja-cobi's transformation method.The feasibility of the measurement system and effectiveness of the reconstruction algorithm aboveare proved by experiment.

A Home-made Simple Set-up for Measurement of Electrochemical Surface Tension Spectrum on a Mercury Drop Electrode

A setup for recording surface tension curves at a mercury drop during potential scanning is designed based on photo-sensitive detection system. Surface tension spectrum at Hg drop can be recorded by voltam0metdc study. A Yb（Ⅲ）-NO2 catalytic reduction system was used for characterization. The simple, sensitive technique can be expected to provide fresh information on molecular interactions at electrode surfaces.

Studies of surface plasmon resonance sensor using bi-beam differential measurement approach

In this paper, a low-cost measurement approach with bi-beam was presented, which can be used for real-time detection and online analysis of solution refractive index, based on systematical analysis and experiments of conventional detection methods on surface plasmon resonance sensor. This novel method was analyzed theoretically and based on it a sensor system set was established. The factors that affect the sensor's sensitivity and working range were discussed. The angular adjustment setup was simplified, errors produced by movable components were avoided and the maneuverability was enhanced with this new method. The noiseproof feature and stability of the sensor system were greatly improved as well.

Time-Resolved Measurements of the Adsorption/Desorption of Rb Atoms on Octadecyltrichlorosilane Coated Surfaces

We carry out the first time-resolved measurement of Rb atoms desorbing from octadecyltrichlorosilane coated sur- faces by polarizing the atoms near the surface using an evanescent wave pump pulse and watching the subsequent intensity change of another evanescent wave probe beam, and find the mean adsorption （dwell） time to be about 400ns at a cell body temperature of 112℃. The adsorption energy is found to be 0.19eV from the surface tem- perature dependence of the adsorption time. This method can be extended to study the adsorption/desorption process of other alkali atoms on other surfaces of transparent substrates with an ultimate time resolution limited by the flight time of atoms in the evanescent wave which is of the order of nanoseconds.

A state-of-the-art review of asphalt pavement surface texture and its measurement techniques

To understand the research status of asphalt pavement texture,the related achievements and progress of pavement surface texture were systematically sorted out from three aspects:the characterization of pavement surface texture,the texture measurement and evaluation,and the relationship between texture and the skid resistance.Based on the statistical geometric characteristics,the spectral characteristics,the fractal characteristics and the multifractal characteristics,the characteristics of pavement texture were discussed.The test methods of pavement texture were divided into two categories:direct measurement methods and indirect measurement methods.The advantages and disadvantages of each measurement method were summarized.The effects of macro-texture and micro-texture on asphalt pavement were discussed,respectively.The relationship between texture and skid resistance was studied.This review shows that multifractal theory should be further studied from the aspect of road engineering.High-precision non-contact integrated detection technology should be further studied to meet the needs of complex testing environments.The method of finite element numerical simulation has potential for the analysis of pavement skid resistance.In addition,methods such as big data analysis,neural network,and deep learning should be studied to achieve the intelligent perception and management of the whole state of skid resistance prediction.

Fast Measurement of Dielectric Conductivity for Space Application by Surface Potential Decay Method

Surface potential decay of polymers for electrical insulation can help to determine the dark conductivity for spacecraft charging analysis. Due to the existence of radiation-induced conductivity, it decays fast in the first few hours after irradiation and exponentially slowly for the remaining time. The measurement of dark conductivity with this method usually takes the slow part and needs a couple of days. Integrating the Fowler formula into the deep dielectric charging equations, we obtain a new expression for the fast decay part. The experimental data of different materials, dose rates and temperatures are fitted by the new expression. Both the dark conductivity and the radiation-induced conductivity are derived and compared with other methods. The result shows a good estimation of dark conductivity and radiation-induced conductivity in high-resistivity polymers, which enables a fast measurement of dielectric conductivity within about 600 rain after irradiation.

STUDY ON MEASUREMENT OF WOOD SURFACEROUGHNESS BY COMPUTER VISION

The working processes, machining devices and tools, cutting amount, consumption of materials, productivity and quality of products are directly affected by wood surface roughness. This paper gives an extensive review of methods used previously to measure wood surface roughness, and concludes that computer vision is the most suitable technique. The preliminary study shows that computer vision method has the advantages of a noncontact, three-dimensional measurement, high speed and well correlates with stylus tracing method. This method can be used in classification and in-time measurement of wood surface roughness after being improved.

A conoscopic holography-based 3D measurement system for analyzing defects in steel plate surface

A conoscopic holography-based 3D measurement system for analyzing the defects on the surface of steel plates was introduced in this paper. The hardware, which is automated through software, performs sampling of the steel plate surface. Through the software interface,point-cloud data of the steel plate surface are obtained and reconstructed to form a 3D image of the steel plate surface. The software allows automatic analysis of steel plate surface detects through identification of the bulges and depressions. In addition, the software can also automatically calculate the defect information ,such as the deepest point, volume, opening area, opening length, and so on, thereby determining the defect size. The results determined by this 3D measurement system were found to be in good agreement with the actual values.

VISION-BASED MEASUREMENT OF FREE-FORM SURFACES

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