Improved formation density measurement using controllable D-D neutron source and its lithological correction for porosity prediction

Controllable D-D neutron sources have a long service life,low cost,and non-radioactivity.There are favorable prospects for its application in geophysical well logging,since traditional chemical radioactive sources used for well logging pose potential threats to the safety of the human body and environment.This paper presents an improved method to measure formation density that employs a D-D neutron source.In addition,the lithological effect on the measured density was removed to better estimate the formation porosity.First,we investigated the spatial distribution of capture gamma rays through Monte Carlo simulations as well as the relationship between the ratio of capture gamma ray counts and formation density to establish theoretical support for the design of density logging tools and their corresponding data processing methods.Second,we obtained the far to near detector counts of captured gamma rays for an optimized tool structure and then established its correlation with the density and porosity of three typical formations with pure quartz,calcite,and dolomite minerals.Third,we determined the values for correcting the densities of sandstone and dolomite with the same porosity using limestone data as the reference and established the equations for calculating the correction values,which lays a solid foundation for accurately calculating formation porosity.We observed that the capture gamma ray counts first increased then decreased and varied in different formations;this was especially observed in high-porosity formations.Under the same lithologic conditions(rock matrix),as the porosity increases,the peak value of gamma ray counts moves toward the neutron source.At different detector-source distances,the ratio of the capture gamma ray counts was well correlated with the formation density.An equation of the formation density conversion was established based on the ratio of capture gamma ray counts at the detector-source distances of 30 cm and 65 cm,and the calculated values were consistent with the true values.After correction,the formation density was highly consistent with the true value of the limestone density,and the mean absolute error was 0.013 g/cm3.The calculated porosity values were very close to the true values,and the mean relative error was 2.33%,highlighting the accuracy of the proposed method.These findings provide a new method for developing D-D neutron source logging tools and their well-log data processing methods.

The Wavefront Power Spectral Density Measurement of Aspheric Lens with Long Focal-Length Using a Computer-Generated Hologram

To ensure the performance of the optical system, the machining accuracy of lens with long focal lengths is required to ensure the image quality. A new method for lens transmission wavefront power spectral density (PSD) in mid-frequency domain measurement using binary phase computer-generated hologram (CGH) is presented. This technique is widely applicable and is particularly useful for measuring large-size lenses with long focal lengths. A comparison experiment of the CGH measurement with results from a Fizeau sphere interferometry method is carried out to verify the accuracy and convenience of the measurement. Furthermore, measurement uncertainty due to CGH fabrication process is analysed. Analysis of the CGH test showed the overall accuracy of less than 1 nm RMS for a sphere lens with over 30 m focal length and Φ410 mm clear aperture. CGH can provide reference spheres with high precision, in the meantime greatly shorten air space, thus reducing the effect of vibration and air turbulence, therefore is of great importance for lens transmission wavefront PSD measurement. The realization of high precision, high efficiency and nondestructive testing of long focal-lens wavefront PSD ensure the ultra-precision and certainty level of machining, hence improving the comprehensive performance of the optical system.

Multi-channel FIR Interferometer for Electron Density Measurement on HT-7 Superconducting Tokamak

A five-channel far-infrared (FIR) hydrogen cyanide (HCN) laser interferometer was developed to measure plasma electron density profile on the HT-7 superconducting tokamak. The principle and structure of the five-channel FIR laser interferometer is described. The laser source used in the interferometer was a continuous wave glow discharge HCN laser with a 3.4 m cavity length and a 100 mW power output at 337μm wavelength. The temporal resolution was 0.1 ms and the detection sensitivity was 1/12 fringe. Preliminary experimental results measured by the interferometer on HT-7 tokamak are reported.

Automated Density Measurement of Weft Knitted Fabrics Using Backlight Imaging

This paper proposes a new density measurement algorithm to address the issues of poor applicability and inaccurate results associated with the automatic density measurement algorithm for weft-knitted fabrics.The algorithm involves collecting the transmitted light image of the knitted fabric,calculating the tilt angle using the skewing correction algorithm,and rotating the image to correct the weft skew present therein.The pre-rotated and post-rotated images are then projected vertically and horizontally in grayscale,and the obtained projection curves are used to represent the distribution of loops in vertical and horizontal rows.This study proposed a wave peak coordinate verification algorithm that calculates the coursewise densities and walewise densities of the knitted fabric.In experiments,the proposed density measurement method is found to exhibit an accuracy above 98%when compared with the manual mode.

Measurement of time-varying electron density of the plasma generated from a small-size cylindrical RDX explosion by Rayleigh microwave scattering

It is challenging to measure the electron density of the unsteady plasma formed by charged particles generated from explosions in the air,because it is transient and on a microsecond time scale.In this study,the time-varying electron density of the plasma generated from a small cylindrical cyclotrimethylenetrinitramine(RDX)explosion in air was measured,based on the principle of microwave Rayleigh scattering.It was found that the evolution of the electron density is related to the diffusion of the detonation products.The application of the Rayleigh microwave scattering principle is an attempt to estimate the electron density in explosively generated plasma.Using the equivalent radius and length of the detonation products in the bright areas of images taken by a high-speed framing camera,the electron density was determined to be of the order of 10^(20)m^(−3).The delay time between the initiation time and the start of variation in the electron-density curve was 2.77–6.93μs.In the time-varying Rayleigh microwave scattering signal curve of the explosively generated plasma,the electron density had two fluctuation processes.The durations of the first stage and the second stage were 11.32μs and 19.20μs,respectively.Both fluctuation processes increased rapidly to a peak value and then rapidly attenuated with time.This revealed the movement characteristics of the charged particles during the explosion.

Single-electromagnet levitation for density measurement and defect detection

This paper presents a single-electromagnet levitation device to measure the densities and detect the internal defects of antimagnetic materials.The experimental device has an electromagnet in its lower part and a pure iron core in the upper part.When the electromagnet is activated,samples can be levitated stably in a paramagnetic solution.Compared with traditional magnetic levitation devices,the single-electromagnet levitation device is adjustable.Different currents,electromagnet shapes,and distances between the electromagnet and iron core are used in the experiment depending on the type of samples.The magnetic field formed by the electromagnet is strong.When the concentration of the MnCl aqueous solution is 3 mol/L,the measuring range of the single-electromagnet levitation device ranges from 1.301 to 2.308 g/cm.However,with the same concentration of MnCl aqueous solution(3 mol/L),the measuring range of a magnetic levitation device built with permanent magnets is only from 1.15 to 1.50 g/cm.The single-electromagnet levitation device has a large measuring range and can realize accurate density measurement and defect detection of high-density materials,such as glass and aluminum alloy.

Characterization of Interface State Density of Ni/p-GaN Structures by Capacitance/Conductance-Voltage-Frequency Measurements

For the frequency range of I kHz-lOMHz, the interface state density of Ni contacts on p-GaN is studied using capacitance-voltage （C-V） and conductance-frequency-voltage （G-f-V） measurements at room temperature. To obtain the real capacitance and interface state density of the Ni/p-GaN structures, the effects of the series resistance （Rs） on high-frequency （SMHz） capacitance values measured at a reverse and a forward bias are investigated. The mean interface state densities obtained from the CHF-CLF capacitance and the conductance method are 2 ×1012 e V-1 cm-2 and 0.94 × 1012 eV-1 cm-2, respectively. Furthermore, the interface state density derived from the conductance method is higher than that reported from the Ni/n-GaN in the literature, which is ascribed to a poor crystal quality and to a large defect density of the Mg-doped p-GaN.

Simultaneous density and velocity measurements in a supersonic turbulent boundary layer

A novel technique for simultaneous measurements of instantaneous whole-field density and velocity fields of supersonic flows has been developed.The density measurement is performed based on the nano-tracer planar laser scattering（NPLS） technique,while the velocity measurement is carried out using particle image velocimetry（PIV）.The present experimental technique has been applied to a flat-plate turbulent boundary layer at Mach 3,and the measurement accuracy of the density and velocity are discussed.Based on this new technique,the Reynolds stress distributions were also obtained,demonstrating that this is an effective means for measuring Reynolds stresses under compressible conditions.

Forward modelling of the Cotton-Mouton effect polarimetry on EAST tokamak

Measurement of plasma electron density by far-infrared laser polarimetry has become a routine and indispensable tool in magnetic confinement fusion research.This article presents the design of a Cotton-Mouton polarimeter interferometer,which provides a reliable density measurement without fringe jumps.Cotton-Mouton effect on Experimental Advanced Superconducting Tokamak(EAST)is studied by Stokes equation with three parameters(s_(1),s_(2),s_(3)).It demonstrates that under the condition of a small Cotton-Mouton effect,parameter s_(2)contains information about Cotton-Mouton effect which is proportional to the line-integrated density.For a typical EAST plasma,the magnitude of Cotton-Mouton effects is less than 2πfor laser wavelength of 432μm.Refractive effect due to density gradient is calculated to be negligible.Time modulation of Stokes parameters(s_(2),s_(3))provides heterodyne measurement.Due to the instabilities arising from laser oscillation and beam refraction in plasmas,it is necessary for the system to be insensitive to variations in the amplitude of the detection signal.Furthermore,it is shown that non-equal amplitude of X-mode and O-mode within a certain range only affects the DC offset of Stokes parameters(s_(2),s_(3))but does not greatly influence the phase measurements of Cotton-Mouton effects.

Optics System Design of Microwave Imaging Reflectometry for the EAST Tokamak

A front-end optics system has been developed for the EAST microwave imaging reflectometry for 2D density fluctuation measurement.Via the transmitter optics system,a combination of eight transmitter beams with independent frequencies is employed to illuminate wide poloidal regions on eight distinct cutoff layers.The receiver optics collect the reflected wavefront and project them onto the vertical detector array with 12 antennas.Utilizing optimized Field Curvature adjustment lenses in the receiver optics,the front-end optics system provides a flexible and perfect matching between the image plane and a specified cutoff layer in the plasma,which ensures the correct data interpretation of density fluctuation measurement.

Review of Computer Vision Applications in Fabric Recognition and Color Analysis

Detecting various parameters of woven fabrics is one of the important methods to evaluate the quality of fabrics.In the early stage of industrial development,fabrics were mainly relied on manual to determine the quality,which was inefficient and unstable,so intelligent inspection is a popular development trend today.In recent years,computer vision technology has been widely used in the fields of fabric density measurement,color analysis,and weave pattern recognition.Based on the above three aspects,the advanced research progress of global researchers is reviewed in this paper and the shortcomings of current research and possible research directions in the future are analyzed.Computer vision technology is not only objective evaluation,but also has the advantages of accuracy and efficiency,and has a good development prospect in the field of textiles.

Inter-Calibration Between Plasma Instruments Onboard DEMETER

The in-situ measurements of the ionospheric plasma that we use come from two instruments of the scientific payload of the satellite DEMETER; the plasma analyser IAP （Instrument d＇analyse du plasma） and the Langmuir probe ISL （Instrument Sonde de Langmuir）. DEMETER is a micro-satellite realized by the CNES（Centre National d＇Etudes Spatiales, France） with a principal objective to seek a possible influence of the seismic activity on the electromagnetic waves in the ionosphere and on the ionospheric plasma. The satellite was placed on June 29, 2004, in a circular and quasi helio-synchronous orbit at -710 km altitude. The experiments function primarily at mid-latitudes （from ＋60° to -60°）. The IAP data were analysed to deduce the ion population （densities of the dominant ions, i.e. generally O^＋, H^＋ and He^＋） therefore the total ion density. The use of data IAP thus requires some precaution to make sure that the electric equilibrium conditions of the satellite, such as the satellite potential （Фsat）, are obtained during the treatment of routine, does not induce an error of measurement. When this potential is negative, the minority light ions H^＋ and He^＋ can be measured in a reliable way when their proportion is above 3% to 5% of that of O^＋. The critical limitation is： under certain conditions, the satellite potential becomes positive and reach a value about -0.5 V so that it becomes impossible to measure H^＋ ions. This is likely to involve a significant error on the composition and the density of the plasma. Therefore we carried out a calibration to estimate the missing density. The ISL experiment （Langmuir probe） provided the collected current/polarized tension characteristics of a cylindrical probe from which both electron density Ne and temperature Te were obtained. In some situations it is necessary to examine the accuracy of the electron density using another technique, for instance the high frequency （HF） spectrogram, provided by ICE （instrument champ electrique） instrument. This technique could give precise information about the accuracy of the data provided by the plasma analyser and the Langmuir probes. The observed satellite surface potential was found to be remarkable and subject of question. It displayed negative values at daytime and positive at night.

X-ray beam hardening correction for measuring density in linear accelerator industrial computed tomography

Due to X-ray attenuation being approximately proportional to material density,it is possible to measure the inner density through Industrial Computed Tomography（ICT） images accurately. In practice,however,a number of factors including the non-linear effects of beam hardening and diffuse scattered radiation complicate the quantitative measurement of density variations in materials. This paper is based on the linearization method of beam hardening correction,and uses polynomial fitting coecient which is obtained by the curvature of iron polychromatic beam data to fit other materials. Through theoretical deduction,the paper proves that the density measure error is less than 2% if using pre-filters to make the spectrum of linear accelerator range mainly 0.3 MeV to 3 MeV. Experiment had been set up at an ICT system with a 9 MeV electron linear accelerator. The result is satisfactory. This technique makes the beam hardening correction easy and simple,and it is valuable for measuring the ICT density and making use of the CT images to recognize materials.

Damage induced by femtosecond laser in optical dielectric films

Both the nature of avalanche ionization （AI） and the role of multi-photon ionization （MPI） in the studies of laser-induced damage have remained controversial up to now. According to the model proposed by Stuart et al., we study the role of MPI and AI in laser-induced damage in two dielectric films, fused silica （FS） and barium aluminum borosilicate （BBS）, irradiated by 780-nm laser pulse with the pulse width range of 0.01 - 5 ps. The effects of MPI and initial electron density on seed electron generation are numerically analyzed. For FS, laser-induced damage is dominated by AI for the entire pulse width regime due to the wider band-gap. While for BBS, MPI becomes the leading power in damage for the pulse width T less than about 0.03 ps. MPI may result in a sharp rise of threshold fluence Fth on r, and AI may lead to a mild increase or even a constant value of Fth on r. MPI serves the production of seed electrons for AI when the electron density for AI is approached or exceeded before the end of MPI. This also means that the effect of initial electron can be neglected when MPI dominates the seed electron generation. The threshold fluence Fth decreases with the increasing initial electron density when the latter exceeds a certain critical value.

Plasma channel formed by ultraviolet laser pulses at 193 nm in air

The propagation of picosecond deep ultraviolet laser pulse at wavelength of 193 nm in air is numerically investigated. Long plasma channel can be formed due to the competition between Kerr self-focusing and ionization induced defocusing. The plasma channel with electron density of above 10^13/cm^3 can be formed over 70 m by 50-ps, 20-mJ laser pulses. The fluctuation of laser intensity and electron density inside ultraviolet （UV） plasma channel is significantly lower UV laser by air is considered in the simulation and it the limit of the length of plasma channel. than that of infrared pulse. The linear absorption of is shown that the linear absorption is important for the limit of the length of plasma channel.

Spectral characteristics of arc plasma during laser-arc double-sided welding for aluminum alloy

In laser-arc double-sided welding, the spectral characteristics of the arc plasma are calculated and analyzed by spectroscopic diagnosis. The results show that, compared with conventional tungsten inert gas （TIG） welding, the introduction of a laser cilanges the physical characteristics of the arc plasma regardless of whether laser plasma penetration takes place, and that the influence of the laser mainly affects the near-anode region of the arc. When tile laser power is relatively low, the arc column tends to compress, and the arc spectral cilaracter- istics show no significant difference. When the arc root constricts, compared with pure TIG arc, the electron density increases by ~2.7 times and the electron temperature decreases by ~3000 K. When the arc column expands, the intensities of spectral lines of both the metal and Ar atoms are the strongest. But it is also observed that the electron density reduces, whereas there is no obvious decrease of electron temperature.

Mixture gas component concentration analysis based on support vector machine and infrared spectrum

A novel quantitative analysis method of multi-component mixture gas concentration based on support vector machine （SVM） and spectroscopy is proposed. Through transformation of the kernel function, the seriously overlapped and nonlinear spectrum data are transformed in high-dimensional space, but the highdimensional data can be processed in the original space. Some factors, such as kernel function, range of the wavelength, and penalty coefficient, are discussed. This method is applied to the quantitative analysis of natural gas components concentration, and the component concentration maximal deviation is 2.28%.

Improved narrow wavelength band blocking filters

A design approach is described to achieve spectral blocking filters of any spectral width and optical density for narrow blocking bands. We give new criterions to find the necessary number of layers from the desired bandwidth and optical density, and give new estimate equations which describe the number of layers required for designing a blocking filter of given bandwidth, high index, and optical density. This approach can be useful for laser line blocking, night vision filters, and many other general applications.

Regional moment-independent sensitivity analysis with its applications in engineering

Traditional Global Sensitivity Analysis（GSA） focuses on ranking inputs according to their contributions to the output uncertainty.However,information about how the specific regions inside an input affect the output is beyond the traditional GSA techniques.To fully address this issue,in this work,two regional moment-independent importance measures,Regional Importance Measure based on Probability Density Function（RIMPDF） and Regional Importance Measure based on Cumulative Distribution Function（RIMCDF）,are introduced to find out the contributions of specific regions of an input to the whole output distribution.The two regional importance measures prove to be reasonable supplements of the traditional GSA techniques.The ideas of RIMPDF and RIMCDF are applied in two engineering examples to demonstrate that the regional moment-independent importance analysis can add more information concerning the contributions of model inputs.