- 标题
- 摘要
- 关键词
- 实验方案
- 产品
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Simulation of photon-counting detectors for conversion of dual-energy-subtracted computed tomography number to electron density
摘要： For accurate tissue-inhomogeneity correction in radiotherapy treatment planning, the author previously proposed a conversion of the energy-subtracted computed tomography (CT) number to electron density (ΔHU–ρe conversion). The purpose of the present study was to provide a method for investigating the accuracy of a photon-counting detector (PCD) used in the ΔHU–ρe conversion by performing dual-energy CT image simulations of a PCD system with two energy bins. To optimize the tube voltage and threshold energy, the image noise and errors in ρe calibration were evaluated using three types of virtual phantoms: a 35-cm-diameter pure water phantom, 33-cm-diameter solid water surrogate phantom equipped with 16 inserts, and another solid water surrogate phantom with a 25-cm diameter. The third phantom was used to investigate the effect of the object’s size on the ρe-calibration accuracy of PCDs. Two different scenarios for the PCD energy response were considered, corresponding to the ideal and realistic cases. In addition, a simple correction method for improving the spectral separation of the dual energies in a realistic PCD was proposed to compensate for its performance loss. In the realistic PCD case, there exists a trade-off between the image noise and ρe-calibration errors. Furthermore, the weakest image noise was nearly twice that for the ideal case, and the ρe-calibration error did not reach practical levels for any threshold energy. Nevertheless, the proposed correction method is likely to decrease the ρe-calibration errors of a realistic PCD to the level of the ideal case, yielding more accurate ρe values that are less affected by object size variation.
关键词： Energy-selective CT,Dual-energy CT,Electron density,Photon-counting detector
更新于2025-09-23 15:22:29
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[IEEE 2018 9th International Conference on Ultrawideband and Ultrashort Impulse Signals (UWBUSIS) - Odessa, Ukraine (2018.9.4-2018.9.7)] 2018 9th International Conference on Ultrawideband and Ultrashort Impulse Signals (UWBUSIS) - The Action of Ultra-Short Super-Powerful Radio Pulses on the Earth's Atmosphere and Ionosphere
摘要： Numerical simulations of disturbances in the electron temperature and density arising from the action of ultra-short super-powerful radio pulses with different durations and powers on the Earth's atmosphere and ionosphere are presented. It is demonstrated that the electron density in the 30–60 km altitude range can be increased by 12 orders of magnitude, while the electron temperature shows an increase of the order of 10 to 100 times. The pulse durations and powers needed to create artificial ionized layers have been estimated.
关键词： ultra-short radio pulse,disturbances,numerical simulation,atmosphere,electron temperature,ionosphere,super-powerful radio pulse,electron density
更新于2025-09-23 15:21:21
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Experiment and simulation calculation of micro-cavity dielectric barrier discharge
摘要： In order to study the discharge mechanism and discharge parameters evolution of micro-cavity dielectric barrier discharge(MDBD), an experimental platform based on the dielectric panel surface grid micro-structure electrode device was built. Discharge equivalent circuit of the MDBD was established based on the deep analysis of the discharge physical process and experimental results. Then, using Matlab/Simulink and BOLSIG+ software， we solved the Kirchhoff’s voltage equation, Boltzmann equation and the electronic continuity equation to obtain the variation of the discharge characteristic parameters, including air gap voltage, the dielectric surface voltage, the electron density and the electron temperature. The results show that the gas gap voltage and dielectric surface voltage are decreased slightly during discharge, the electron temperature and electron density are consistent with the variation of discharge current. The maximum electron temperature is about 3.0eV, the average value is about 1.6eV, and its value is lower than the conventional dielectric barrier discharge(DBD).
关键词： Micro-cavity,Electron Temperature,Dielectric Barrier Discharge,Gas Gap Voltage,Electron Density
更新于2025-09-23 15:21:21
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RESEARCH ON MINIMUM ENERGY EXCITED TO PLASMA COATING FOR REDUCING RADAR CROSS SECTION OF TARGET
摘要： To reduce the radar cross section (RCS) of a target, plasma coating on perfectly electric conducting plate is studied in this paper. Nonuniform helium plasma produced by a minitype solid rocket engine is with collisional and unmagnetized. Energy excited for generating helium plasma is investigated. Based on the collisional, unmagnetized, and cold plasma model, backscattering RCS is computed by using ?nite-di?erence time-domain method. Principle of RCS reduction is explained. To ?nd minimum input energy while RCS reduced, relationship between input power and RCS reduction is discussed, and numerical optimization is also implemented. We can identify optimal parameters and choose the best electron density pro?le under condition of given input power level.
关键词： Radar Cross Section (RCS),Plasma Coating,Input Power,Electron Density,Finite-Difference Time-Domain (FDTD) Method
更新于2025-09-23 15:21:21
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An investigation of the ionospheric F?region near the EIA crest in India using OI 777.4 and 630.0?nm nightglow observations
摘要： Simultaneous observations of OI 777.4 and OI 630.0 nm nightglow emissions were carried at a low-latitude station, Allahabad (25.5? N, 81.9? E; geomag. lat. ～ 16.30? N), located near the crest of the Appleton anomaly in India during September–December 2009. This report attempts to study the F region of ionosphere using airglow-derived parameters. Using an empirical approach put forward by Makela et al. (2001), firstly, we propose a novel technique to calibrate OI 777.4 and 630.0 nm emission intensities using Constellation Observing System for Meteorology, Ionosphere, and Climate/Formosa Satellite Mission 3 (COSMIC/FORMOSAT-3) electron density profiles. Next, the electron density maximum (Nm) and its height (hmF2) of the F layer have been derived from the information of two calibrated intensities. Nocturnal variation of Nm showed the signatures of the retreat of the equatorial ionization anomaly (EIA) and the midnight temperature maximum (MTM) phenomenon that are usually observed in the equatorial and low-latitude ionosphere. Signatures of gravity waves with time periods in the range of 0.7–3.0 h were also seen in Nm and hmF2 variations. Sample Nm and hmF2 maps have also been generated to show the usefulness of this technique in studying ionospheric processes.
关键词： OI 777.4 nm,EIA crest,equatorial ionization anomaly,COSMIC/FORMOSAT-3,midnight temperature maximum,nightglow observations,OI 630.0 nm,gravity waves,ionospheric F region,electron density profiles
更新于2025-09-23 15:21:21
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Direct quantitative material decomposition employing grating-based X-ray phase-contrast CT
摘要： Dual-energy CT has opened up a new level of quantitative X-ray imaging for many diagnostic applications. The energy dependence of the X-ray attenuation is the key to quantitative material decomposition of the volume under investigation. This material decomposition allows the calculation of virtual native images in contrast enhanced angiography, virtual monoenergetic images for beam-hardening artifact reduction and quantitative material maps, among others. These visualizations have been proven beneficial for various diagnostic questions. Here, we demonstrate a new method of ‘virtual dual-energy CT’ employing grating-based phase-contrast for quantitative material decomposition. Analogue to the measurement at two different energies, the applied phase-contrast measurement approach yields dual information in form of a phase-shift and an attenuation image. Based on these two image channels, all known dual-energy applications can be demonstrated with our technique. While still in a preclinical state, the method features the important advantages of direct access to the electron density via the phase image, simultaneous availability of the conventional attenuation image at the full energy spectrum and therefore inherently registered image channels. The transfer of this signal extraction approach to phase-contrast data multiplies the diagnostic information gained within a single CT acquisition. The method is demonstrated with a phantom consisting of exemplary solid and fluid materials as well as a chicken heart with an iodine filled tube simulating a vessel. For this first demonstration all measurements have been conducted at a compact laser-undulator synchrotron X-ray source with a tunable X-ray energy and a narrow spectral bandwidth, to validate the quantitativeness of the processing approach.
关键词： Dual-energy CT,virtual non-contrast images,grating-based phase-contrast,electron density,effective atomic number,material decomposition,quantitative X-ray imaging,virtual monoenergetic images
更新于2025-09-23 15:21:21
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Investigation into the Effect of Increasing Target Temperature and the Size of Cavity Confinements on Laser-Induced Plasmas
摘要： In this work, the effect of the sample temperature on the magnesium (Mg) and titanium (Ti) plasmas generated by a Q-switched Neodymium-doped Yttrium Aluminum Garnet (Nd:YAG) laser operating at its fundamental wavelength of 1064 nm has been investigated. We observed that increasing the sample temperature significantly enhanced the emission intensities of the plasmas. Comparing the emission peak intensities of the case of 100°C to the case of 300°C, we recorded a substantial enhancement of the peak intensities of the latter compared to the former. From these results it can be observed that increasing the sample temperature has a significant effect on the emission intensities of the plasmas. We also studied the plasma dynamics and found that increasing the sample temperature also decreases the air density around the Mg sample surface. The reduction in the air density resulted in a decrease in the radiation process and lowers collision probability. Furthermore, as the plasma expands, the plasma pressure also decreases. In addition, we also employed circular and square cavities to confine the titanium plasma, and investigated the effect of the sizes of the circular and square cavities on the titanium plasma. We observed a general improvement in the emission intensities with both the circular and square cavities and attributed this improvement to the plasma compression effect of the shock waves produced by the plasma within the cavities.
关键词： electron temperature,LIBS,Mg-alloy,electron density,cavity confinement,Ti-alloy
更新于2025-09-23 15:21:01
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Investigation on the effects of laser parameters on the plasma profile of copper using picosecond laser induced plasma spectroscopy
摘要： Laser induced plasma generation and characterization, affected by laser parameters and sample physical properties, represent important phenomena in many fields of applications. In this work, we present new studies on the effects of an appropriate combination of laser wavelengths and pulse energies on the generated plasma characterization using a single shot picosecond Nd:YAG laser. The plasma plume of a pure copper sample has been generated by laser induced plasma spectroscopy (LIPS) using a single shot 170 ps laser pulse with wavelengths (266, 355, 532 and 1064 nm) and varying laser fluence (10–41 J/cm2). The spectral intensities of Cu I 324.75, 327.39, 515.32 and 521.82 nm have been observed. The plasma electron temperature and density have been determined from the Boltzmann plots and Stark-broadening profiles of the plasma spectral lines, respectively, assuming the local thermodynamic equilibrium (LTE) condition. It has been found that the electron temperature and electron density values increase from around 10,000 to 20,000 K and around 2 × 1017 to 1.5 × 1018 cm?3, respectively, with the increase in the laser wavelength and pulse fluence gradually. These observations can be understood due to the variations of mass-ablation rates, inverse-Bremsstrahlung, and photo-ionization with the studied pulse wavelength and pulse energy. The obtained results explore the opportunity to control specific generated plasma parameters by applying proper picosecond pulse parameters which can be considered in many fields of material science spectroscopic analysis and control the plasma interaction dynamics.
关键词： Stark-broadening,Picosecond,Boltzmann plot,Electron temperature,LTE,Laser induced plasma spectroscopy,Copper,Electron density,Plasma plume,LIPS
更新于2025-09-23 15:21:01
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Generation-recombination voltage noise spectrum in uniformly doped majority-carrier semiconductor samples
摘要： The formula for the voltage noise spectrum due to generation-recombination (G-R) rate fluctuations is derived for uniformly doped majority-carrier n-type semiconductor samples. In the derivation of the formula, the ohmic boundary condition is used to obtain physically sound results, correcting and extending the previously published formulas. It is shown that the G-R voltage noise spectrum becomes saturated in the high electric field region, which is the signature feature of the G-R noise. Furthermore, the electron density fluctuation is developed and calculated due to the delta-function population source. It is shown that as the electric field increases, the profile of the electron density fluctuation becomes quite asymmetric due to the strong drift velocity, and the peak value of the electron density fluctuation at the delta-function source location decreases, resulting in the saturation of the G-R noise voltage spectrum at high electric fields.
关键词： generation-recombination noise,voltage noise spectrum,semiconductor,electron density fluctuation,electric field
更新于2025-09-23 15:21:01
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[IEEE 2019 IEEE Pulsed Power & Plasma Science (PPPS) - Orlando, FL, USA (2019.6.23-2019.6.29)] 2019 IEEE Pulsed Power & Plasma Science (PPPS) - Laser Thomson Scattering Diagnostics for Streamer Discharge in HE Gas
摘要： Streamer discharge plasma, a type of non-thermal plasma, has received global attention as a source of reactive radicals, and is used for many applications such as ozone generation, decomposition of NOx and other gas pollutants, cleaning water, disinfection, deodorization, and medical applications. The tip of streamer discharge, known as the streamer head, in particular contributes to radical production. The peak electric field is located on the streamer head on the axis of symmetry of the discharge, likely resulting in many radical types. Very remarkable results in NO removal efficiency and superior ozone generation yield performed by streamer discharge have reported. Improving gas treatment methods requires understanding of physical characteristics of streamer discharge and streamer head, for example, electron temperature and electron density. This study investigates characteristics of streamer discharge by observing the propagation process of streamer head in a needle to conic electrode with positive voltage using a high speed gated emICCD camera. Then, incoherent laser Thomson scattering (LTS) diagnostic for streamer discharge and streamer head with positive voltage was performed. LTS diagnostic is considered to be the most reliable technique measuring electron temperature and density in plasma simultaneously. In addition, LTS diagnostic has high resolution temporally and spatially, therefore, LTS diagnostic can measure location dependence of electron temperature and density in streamer discharge including streamer head. The measurement point was 1 mm and 2 mm from tip of the high voltage needle electrode, and Thomson scattering signals were measured at the point of initial phase of streamer head propagation. In the results, electron temperature of streamer discharge was 4 to 6 eV, electron density of streamer discharge was 1021 m-3 order. This study has proven that LTS diagnostic can measure electron temperature and density in streamer discharge plasma.
关键词： Streamer discharge,Electron temperature,Laser Thomson scattering,Non-thermal plasma,Electron density
更新于2025-09-23 15:19:57