- 标题
- 摘要
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- 实验方案
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Development of a sub-miniature gamma camera for multimodal imaging system
摘要： In the recent past, gamma-ray imaging detectors have achieved an intrinsic spatial resolution of less than 1 mm within a few centimeters of a useful field of view (UFOV). Unlike to conventional gamma cameras, which are large and heavy, the compact gamma-ray imaging detectors can improve the performances of the gamma cameras used in the various fields. In this study, we developed a sub-miniature gamma camera for a multimodal imaging system. The camera has a gamma-ray detector, miniature electronics modules, and a diverging hole collimator. The detector consisted of the sub-millimeter pixelated Ce:GAGG array and the silicon photomultiplier (SiPM) array module. We organized the miniature electronics modules according to the functions; an MPPC base board, analog signal processing board, integrated power supply board, and compact data acquisition (DAQ) base board. The diverging hole collimator widened an imaging area of the gamma camera from the UFOV of the detector. On the detector side, dimensions of each hole and septa were identical to the pixel and inter-pixel thickness of the reflector of scintillator array. For the intrinsic performance test, we acquired a flood map image of 729 (27 × 27) scintillator pixels, and the energy resolution was 18.9 % for an integrated energy histogram of 99mTc (140 keV). For the extrinsic performance test, we used the 57Co sheet source, and made a 99mTc line source using a capillary tube. The sources located at 10 cm apart from the collimator surface. The imaging area was three times wider than the UFOV of the detector. The system sensitivity was 19 CPM/μCi and the spatial resolution was 3.5 mm. The usability of the proposed gamma camera will not be confined to existing applications due to its compactness and novelty.
关键词： Sub-miniature gamma camera,Gamma camera performance evaluation,Front-end electronics,Multimodal imaging system,Diverging hole collimator
更新于2025-09-23 15:23:52
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[IEEE 2018 17th International Conference on Ground Penetrating Radar (GPR) - Rapperswil, Switzerland (2018.6.18-2018.6.21)] 2018 17th International Conference on Ground Penetrating Radar (GPR) - Full Waveform Inversion of Cross-hole Radar Data Using Envelope Objective Function
摘要： The full waveform inversion (FWI) has been used as a high resolution imaging method for cross-hole radar inversion implementation, however, when FWI is used to process field data, it encounters a variety of problems and causes the inversion to fall into a local minimum. One problem is that the GPR data lacks low frequency information. An effective way is to provide an accurate initial model for FWI. The fact is that the underground media is unknown which results in difficult to obtain ideal result in FWI. By means of the derivation of the objective function, the gradient formula of the envelope waveform inversion (EWI) is derived by taking the derivation of the EWI misfit function with respect to the model parameter. By comparing the inversion results of the EWI with that of the traditional FWI without low-frequency information in the observed GPR data, we found that the EWI can effectively restore missing low-frequency information and has better inversion ability for low-frequency missing data.
关键词： cross-hole radar,envelope,full waveform inversion,low frequency component,initial model
更新于2025-09-23 15:23:52
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[IEEE 2018 2nd IEEE Conference on Energy Internet and Energy System Integration (EI2) - Beijing, China (2018.10.20-2018.10.22)] 2018 2nd IEEE Conference on Energy Internet and Energy System Integration (EI2) - Study on Fractal Butterfly Antenna Sensors Detecting Partial Discharge UHF Signal Propagating from GIS Placing Hole
摘要： Detecting the Ultra-High Frequency (UHF) electromagnetic wave has been acknowledged as an effective method in the measurement of varied kinds of partial discharges in Gas Insulated Switchgear (GIS). However, electromagnetic wave has been shielded completely owing to the steel flange around the insulator in recent years. Detecting the electromagnetic wave propagating from the placing hole in the steel flange becomes the only practicable method. The traditional sensors enter a bottleneck stage when they are used to detecting the electromagnetic wave propagating from the placing hole. The sensitivity declines a lot and output signal becomes weaker. At present, there are no relevant sensors, which detecting UHF electromagnetic wave propagating from placing hole. By adopting the fractal technology, back cavity and loaded resistor, the UHF sensor of fractal butterfly antenna was developed based on the software of High Frequency Structure Simulator(HFSS). Equivalent height was tested in the platform of Giga hertz Transverse Electromagnetic(GTEM) chamber. Detection sensibility and validity was professionally tested via applied in an experimental platform of 220kV GIS. It is concluded that the fractal butterfly antenna sensor belongs to the linear polarized antenna. The available frequency range is concentrated in 0.8-2GHz. The average equivalent height of fractal butterfly antenna is twice more than the traditional sensors. Detecting sensitivity of partial discharge is lower than 20pC.
关键词： placing hole,GIS,partial discharge,fractal butterfly antenna
更新于2025-09-23 15:23:52
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Dense Electron-Hole Plasma Formation and Ultra-Long Charge Lifetime in Monolayer MoS <sub/>2</sub> via Material Tuning
摘要： Many-body interactions in photoexcited semiconductors can bring about strongly-interacting electronic states, culminating in the fully-ionized matter of electron-hole plasma (EHP) and electron-hole liquid (EHL). These exotic phases exhibit unique electronic properties, such as metallic conductivity and metastable high photoexcitation density, which can be the basis for future transformative applications. However, the cryogenic condition required for its formation has limited the study of dense plasma phases to a purely academic pursuit in a restricted parameter space. This paradigm can potentially change with the recent experimental observation of these phases in atomically thin MoS2 and MoTe2 at room temperature. A fundamental understanding of EHP and EHL dynamics is critical for developing novel applications on this versatile layered platform. In this work, we studied the formation and dissipation of EHP in monolayer MoS2. Unlike previous results in bulk semiconductors, our results reveal that electro-mechanical material changes in monolayer MoS2 during photoexcitation play a significant role in dense EHP formation. Within the free-standing geometry, photoexcitation is accompanied by an unconstrained thermal expansion, resulting in a direct-to-indirect gap electronic transition at a critical lattice spacing and fluence. This dramatic altering of the material’s energetic landscape extends carrier lifetimes by 2 orders of magnitude and allows the density required for EHP formation. The result is a stable dense plasma state that’s sustained with modest optical photoexcitation. Our findings pave the way for novel applications based on dense plasma states in 2D semiconductors.
关键词： 2D materials,Dense Electron-Hole Plasma,Bandgap Renormalization,MoS2,Transition Metal Dichalcogenides,Direct to Indirect Bandgap Transition
更新于2025-09-23 15:23:52
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Localized Surface Plasmon Resonance Sensor Based at Metallic Sphere Dimer Particle
摘要： By the cooling holes in aero-engine turbine blade as the research object, this study focuses on two kinds of electrochemical machining(ECM) methods, which are mix gas added to the nonlinear electrolyte (NaNO3) and non-mixed gas. Mixed and non-mixed gas ECM experiments of turbine blade cooling holes were carried out respectively. The corresponding two-dimensional CAD model of cooling hole was constructed combined with the experimental data and theoretical analysis. Numerical simulation analysis was carried out of the flow field base on the above models by using the fluid dynamics analysis software FLUENT. The influence flow velocity and flow velocity distribution on the machining accuracy and efficiency of ECM were investigated in detail. The vortex zone distribution of gas-NaNO3 mixed phase flow field and single NaNO3 solution flow field was analyzed qualitatively. The simulation results indicated that the flow velocity in the machining gap with mixed gas was significantly higher than the velocity during ECM process for cooling holes. The electrolytic products and heat were washed away completely, the electrolyte can be updated in time. Fluid vortex zone distribution was improved obviously, the flow field distribution became more uniform after mixed gas in ECM process. The machining accuracy and efficiency for cooling holes making may be improved greatly with gas mixed in electrolyte NaNO3.
关键词： electrolytic machining,mixed gas,cooling hole,gas-liquid two-phase flow,CFD
更新于2025-09-23 15:22:29
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NuSTAR observations of Mrk 766: distinguishing reflection from absorption
摘要： We present two new NuSTAR observations of the narrow-line Seyfert 1 (NLS1) galaxy Mrk 766 and give constraints on the two scenarios previously proposed to explain its spectrum and that of other NLS1s: relativistic reflection and partial covering. The NuSTAR spectra show a strong hard (>15 keV) X-ray excess, while simultaneous soft X-ray coverage of one of the observations provided by XMM–Newton constrains the ionized absorption in the source. The pure reflection model requires a black hole of high spin (a > 0.92) viewed at a moderate inclination (i = 46+1?4°). The pure partial covering model requires extreme parameters: the cut-off of the primary continuum is very low (22+7?5 keV) in one observation and the intrinsic X-ray emission must provide a large fraction (75 per cent) of the bolometric luminosity. Allowing a hybrid model with both partial covering and reflection provides more reasonable absorption parameters and relaxes the constraints on reflection parameters. The fractional variability reduces around the iron K band and at high energies including the Compton hump, suggesting that the reflected emission is less variable than the continuum.
关键词： accretion, accretion discs,galaxies: individual: Mrk 766,galaxies: Seyfert,black hole physics
更新于2025-09-23 15:22:29
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Carrier Transport Mechanisms Underlying the Bidirectional VTH Shift in p-GaN Gate HEMTs Under Forward Gate Stress
摘要： The threshold voltage (VTH) instability of p-GaN/AlGaN/GaN HEMTs was investigated under forward gate stress. A unique bidirectional VTH shift (ΔVTH) with the critical gate voltage (VG) of 6 V was observed. The carrier transport mechanisms underlying the ΔVTH were extensively investigated through the voltage-dependent, time-resolved, and temperature-dependent gate current. The gate current is decomposed into electron and hole current in three distinct regions with respect to VG, which are off-state for VG < 1.2 V (VTH), on-state for 1.2 V < VG < 5 V and “gate-injected” region for VG > 5 V. In off-state, the electrons were thermally activated and transport towards the gate, while electron-trapping governed by the space charge limited conduction (SCLC) in AlGaN barrier was observed in on-state and “gate-injected” region. Such an electron-trapping effect results in the positive VTH shift for VG < 6 V. Meanwhile, the marginal hole transport from gate by thermal activation was also captured by gate current, which features negligible impact on VTH. However, for VG > 6 V, a drastic hole injection triggered by high VG takes place that causes subsequent hole-trapping in AlGaN barrier and hole-injection into GaN buffer. The injected holes enhance the positive charge in the gate region and turned the positively shifted VTH into a negative shift.
关键词： hole injection,threshold voltage shift,p-GaN HEMT,electron trapping,carrier transport mechanisms,gate stress
更新于2025-09-23 15:22:29
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Spectral versus Time-Domain OCT in Detecting Preoperative Epiretinal Membranes that Accompany Macular Holes
摘要： Purpose: To compare the sensitivities of spectral-domain optical coherence tomography (SD-OCT) versus time-domain OCT (TD-OCT) in identifying epiretinal membranes (ERM) preoperatively in patients who underwent surgery for full-thickness macular holes (FTMH). Methods: This is an interventional retrospective case series of 59 eyes diagnosed with FTMHs who underwent 25-G pars plana vitrectomy with internal limiting membrane peeling between 2009 and 2015. Preoperative OCTs were obtained by SD-OCT (Spectralis, Heidelberg, Germany) or TD-OCT (Stratus, Carl Zeiss Meditec, Dublin, CA, USA). Volume scans were reviewed for ERM accompanying the FTMH. This was compared to indocyanine green-negative staining and intraoperative findings of ERM as the gold standard. Results: Baseline characteristics between the SD-OCT and TD-OCT groups were comparable. Mean duration of postoperative follow-up was 41.4 weeks (±49.0). Of 59 eyes, 33 (55.9%) exhibited an ERM intraoperatively. Four ERMs (SD-OCT group) compared to 12 (TD-OCT group) were not visualized on preoperative OCT (p = 0.003). Sensitivity and specificity of SD-OCT in ERM detection was 79% and 100% compared to 14% and 91% for TD-OCT. Visual acuity improved in both arms (0.5 and 0.3 logMAR units in SD-OCT and TD-OCT, respectively (p = 0.002, 0.0002). Conclusions: We found that SD-OCT was superior to TD-OCT in identifying the presence of ERM preoperatively in patients who underwent macular hole surgery. Since ERMs may decrease the chance of successful pharmacologic vitreolysis, we recommend using SD-OCT over TD-OCT in the evaluation of patients with FTMH to more accurately identify ERMs and allow more comprehensive treatment decisions (pharmacologic versus surgical).
关键词： Epiretinal membrane,Spectral-domain optical coherence tomography,Macular hole,Time-domain optical coherence tomography
更新于2025-09-23 15:22:29
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Fast and slow interface traps in transparent NiO gated AlGaN/GaN heterostructure field-effect transistors
摘要： In the present study, the reliability of transparent NiO gated AlGaN/GaN heterostructure field-effect transistors have been investigated. Compared with the TiN Schottky gated device, the p-NiO electrode can suppress the gate leakage and shift the threshold voltage positively. Pulse-mode and temperature-dependent current-voltage measurements demonstrate that both kinds of devices present good stability. The frequency-dependent conductance measurement confirms that only fast trap is detected for the TiN gated device while both fast and slow traps for the NiO gated one. The slow trap is ascribed to the hole trapping in the type-II staggered band configuration between NiO and AlGaN/GaN, which is also confirmed from the obvious threshold voltage instability in high frequency loop scan curves.
关键词： p-NiO,Hole trapping,Reliability,Transparent gate
更新于2025-09-23 15:22:29
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Effect of electron-donating groups on the electrochemical and optical properties of indoline substituents as hole transport materials: A computational study
摘要： The e?ect of electron-donating property of the groups attached to the indoline substituents with two di?erent low-cost cores (tetraazafulvalene and pyrene) as new hole transport materials (HTMs) was studied on their electrochemical and optical behaviors. The calculations were carried out based on the theoretical approaches including density functional theory (DFT), time-dependent density functional theory (TD-DFT), and Marcus theory. Some important parameters, such as hole mobility, solubility and stability, absorption and emission spectra, Stokes shift, and HOMO/LUMO energies and distributions were obtained and discussed. It was found that the HOMO of all the designed structures is distributed more widely than their LUMO. The results showed that the maximum absorption band of the designed HTMs is red shifted as the electron-donating ability increases. It is also predicted that TAF/indoline-OMe and Py/indoline-NH2 with the hole mobility of 2.90 × 10?3 and 1.51 × 10?3 cm2 V?1 s?1, respectively give higher ?ll factor and short-circuit current density of the device.
关键词： Hole transporting materials,Perovskite solar cells,Di?erent electron-donating groups,Indoline substituents,DFT/TD-DFT,Cost e?ective
更新于2025-09-23 15:22:29