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Design and performance evaluation of high resolution small animal PET scanner based on monolithic crystal: a simulation study
摘要： Dedicated small-animal PET scanners functionality can be optimized by improving the sensitivity and spatial resolution of the scanner. Approximately most of the developed and commercially available small-animal PET scanners are equipped with pixelated scintillators; therefore, their spatial resolution is limited to the crystal pixel size. Complex fabrication, low-sensitivity, and disability in depth of interaction calculation (DOI) are the major disadvantages of pixelated crystals. However, monolithic scintillator crystals are known as one of the most commonly used substitutions, as they have higher sensitivity, DOI recognition, and lower cost. We already designed and implemented a dedicated small-animal PET scanner based on pixelated scintillator crystals and silicon photomultiplier (SiPM). In this study, we plan to present a new optimized design based on the monolithic crystal, with similar performance by the previous scanner. Then we would optimize the thickness of the monolithic crystals for animal PET scanners as a function of sensitivity and spatial resolution. All simulations were performed based on GEANT4, a validated Monte Carlo toolkit. We simulated a recently fabricated scanner with pixelated crystals and compared it with a simulated scanner based on an optimized monolithic crystal. The experimental setup used for comparison and validation is a small Animal PET consisting of ten pixelated modules. This study anticipates that by replacing a pixelated crystal (consist of 24 × 24 LYSO elements, and 2 × 2 × 10 mm3 crystal size) with a monolithic crystal (with 8 mm thickness and 50.2 × 50.2 entrance area), the average spatial resolution stays the same and sensitivity grows ～ 17% in the center of AFOV and also the fabrication cost dives remarkably. Simulation reveals that although the depth of interaction DOI was not taken into consideration, the crystals with 6 mm thickness have acceptable spatial resolution (～ 1.3 mm FWHM at the centre of the AFOV) and relatively good absolute sensitivity (～ 1.6%).
关键词： SPECT,coronary CT angiography (CTA),PET PET/CT,Gamma camera,Models and simulations
更新于2025-09-23 15:22:29
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A radiative transfer module for calculating photolysis rates and solar heating in climate models: Solar-J v7.5
摘要： Solar-J is a comprehensive radiative transfer model for the solar spectrum that addresses the needs of both solar heating and photochemistry in Earth system models. Solar-J is a spectral extension of Cloud-J, a standard in many chemical models that calculates photolysis rates in the 0.18–0.8 μm region. The Cloud-J core consists of an eight-stream scattering, plane-parallel radiative transfer solver with corrections for sphericity. Cloud-J uses cloud quadrature to accurately average over correlated cloud layers. It uses the scattering phase function of aerosols and clouds expanded to eighth order and thus avoids isotropic-equivalent approximations prevalent in most solar heating codes. The spectral extension from 0.8 to 12 μm enables calculation of both scattered and absorbed sunlight and thus aerosol direct radiative effects and heating rates throughout the Earth’s atmosphere. The Solar-J extension adopts the correlated-k gas absorption bins, primarily water vapor, from the shortwave Rapid Radiative Transfer Model for general circulation model (GCM) applications (RRTMG-SW). Solar-J successfully matches RRTMG-SW’s tropospheric heating profile in a clear-sky, aerosol-free, tropical atmosphere. We compare both codes in cloudy atmospheres with a liquid-water stratus cloud and an ice-crystal cirrus cloud. For the stratus cloud, both models use the same physical properties, and we find a systematic low bias of about 3 % in planetary albedo across all solar zenith angles caused by RRTMG-SW’s two-stream scattering. Discrepancies with the cirrus cloud using any of RRTMG-SW’s three different parameterizations are as large as about 20–40 % depending on the solar zenith angles and occur throughout the atmosphere. Effectively, Solar-J has combined the best components of RRTMG-SW and Cloud-J to build a high-fidelity module for the scattering and absorption of sunlight in the Earth’s atmosphere, for which the three major components – wavelength integration, scattering, and averaging over cloud fields – all have comparably small errors. More accurate solutions with Solar-J come with increased computational costs, about 5 times that of RRTMG-SW for a single atmosphere. There are options for reduced costs or computational acceleration that would bring costs down while maintaining improved fidelity and balanced errors.
关键词： solar heating,clouds,Cloud-J,climate models,radiative transfer,photolysis rates,scattering,aerosols,RRTMG-SW,Solar-J
更新于2025-09-23 15:22:29
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Strain control of GaN grown on Si substrates using an AlGaN interlayer
摘要： To suppress wafer bowing and crack generation of GaN on Si substrates, we investigated the effects of the Al content and thickness of the AlGaN interlayer on the compressive strain in the overlying GaN layer theoretically and experimentally. In the simulation, AlGaN relaxes gradually over the critical thickness. Therefore, the relaxation ratio of AlGaN at the top surface can be defined as a function of Al content and thickness. Too high Al content or too thick AlGaN interlayer induced too large initial strain in the upper GaN layer, which caused rapid and succeeding gradual relaxation, i.e., decrease of strain, of the GaN layer during growth because of generation of threading dislocations. Conversely, low Al content or thin AlGaN interlayer could induce constant but only small strain in the GaN layer. Therefore, the ideal relaxation ratio of the AlGaN surface exists to apply the maximal constant compressive strain in the GaN layer. The relaxation ratios of AlGaN interlayers determined in experiments were much smaller than those calculated in the simulation. Although the measured compressive strain in the GaN layer was smaller than expected, its decrease rate was small when grown on AlGaN interlayers with an almost ideal relaxation ratio.
关键词： Computer simulation,Characterization,Metalorganic vapor phase epitaxy,Stresses,Growth models,Nitrides
更新于2025-09-23 15:22:29
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Measurements of Beamswitching Gains and Fade Dynamics for 28 GHz Indoor Static Links in the Presence of Pedestrian Traffic
摘要： We measured channel dynamics for fixed wireless indoor channels at 28 GHz. We characterize pedestrian-induced fades in open indoor spaces and the effectiveness of beamswitching to mitigate them. We find that fades of the dominant propagation path may be as deep as 9 dB at the 90th percentile and that alternative signal paths are typically not strong enough to provide significant beamswitching gains.
关键词： Millimeter wave propagation,Rician channels,Channel models,Multipath channels,Fading channels
更新于2025-09-23 15:22:29
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Joint Color Space GMMs for CFA Demosaicking
摘要： We propose a patch-based algorithm for demosaicking a mosaicked color image produced by color filter arrays commonly used in acquiring color images. The proposed algorithm exploits a joint color space Gaussian mixture model (JCS-GMM) prior for jointly characterizing the patches from red, green, and blue channels of a color image. The inter channel correlations captured by the covariance matrices of Gaussian models are exploited to estimate the pixel values missing in the mosaicked image. The proposed JCS-GMM demosaicking algorithm can be seen as the GMM analogue of the Color-KSVD algorithm, which has produced impressive results in color image denoising and demosaicking. We demonstrate that our proposed algorithm achieves superior performance in the case of Kodak and Laurent Condat’s databases, and competitive performance in the case of IMAX database, when compared with state-of-the-art demosaicking algorithms.
关键词： Color filter array,demosaicking,Bayer pattern,Gaussian mixture models
更新于2025-09-23 15:22:29
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[IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Recent Advances and Opportunities in Scene Classification of Aerial Images with Deep Models
摘要： Scene classification is a fundamental task in interpretation of remote sensing images, and has become an active research topic in remote sensing community due to its important role in a wide range of applications. Over the past years, tremendous efforts have been made for developing powerful approaches for scene classification of remote sensing images, evolving from the traditional bag-of-visual-words model to the new generation deep convolutional neural networks (CNNs). The deep CNN based methods have exhibited remarkable break-through on performance, dramatically outperforming previous methods which strongly rely on hand-crafted features. However, performance with deep CNNs has gradually plateaued on existing public scene datasets, due to the notable drawbacks of these datasets, such as the small scale and low-diversity of training samples. Therefore, to promote the development of new methods and move the scene classification task a step further, we deeply discuss the existing problems in scene classification task, and accordingly present three open directions. We believe these potential directions will be instructive for the researchers in this field.
关键词： Scene classification,deep models,domain adaptation,datasets,scene caption
更新于2025-09-23 15:22:29
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[IEEE 2018 41st International Conference on Telecommunications and Signal Processing (TSP) - Athens, Greece (2018.7.4-2018.7.6)] 2018 41st International Conference on Telecommunications and Signal Processing (TSP) - Depth Estimation and Ray Tracing Model Selection of Buried Utilities on Ground Penetrating Radar Data
摘要： When assessing a target depth from a Ground Penetrating Radar (GPR) image, one typically assumes a certain wave propagation model as well as the model parameters (typically the dielectric of the medium). While much work has been conducted on the automatic inference of the model parameters, not much work has been performed testing the validity of the model itself. The work presented here closes this gap for a low-frequency GPR system (350 MHz center frequency). It compares the measurement, taken from known targets at known depths, with different ray propagation models. It also presents a novel method for efficiently estimating the depth of a target without using any knowledge of the medium's wave propagation speed, or even the time of the signal's emission from the transmitter (time zero). Experiments on 26 targets of varying depths showed an averaged estimation error of less than 0.5%, with a standard deviation of 3% using this robust and efficient method.
关键词： GPR,Wave Propagation,Ray Tracing Models,Target Depth Estimation
更新于2025-09-23 15:22:29
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A Strategy to Optimize the Generation of Stable Chromobody Cell Lines for Visualization and Quantification of Endogenous Proteins in Living Cells
摘要： Single-domain antibodies have emerged as highly versatile nanoprobes for advanced cellular imaging. For real-time visualization of endogenous antigens, fluorescently labelled nanobodies (chromobodies, CBs) are introduced as DNA-encoded expression constructs in living cells. Commonly, CB expression is driven from strong, constitutively active promoters. However, high expression levels are sometimes accompanied by misfolding and aggregation of those intracellular nanoprobes. Moreover, stable cell lines derived from random genomic insertion of CB-encoding transgenes bear the risk of disturbed cellular processes and inhomogeneous CB signal intensities due to gene positioning effects and epigenetic silencing. In this study we propose a strategy to generate optimized CB expressing cell lines. We demonstrate that expression as ubiquitin fusion increases the fraction of intracellularly functional CBs and identified the elongation factor 1α (EF1-α) promoter as highly suited for constitutive CB expression upon long-term cell line cultivation. Finally, we applied a CRISPR/Cas9-based gene editing approach for targeted insertion of CB expression constructs into the adeno-associated virus integration site 1 (AAVS1) safe harbour locus of human cells. Our results indicate that this combinatorial approach facilitates the generation of fully functional and stable CB cell lines for quantitative live-cell imaging of endogenous antigens.
关键词： chromobodies,live-cell imaging,cellular models,compound screening,nanobodies
更新于2025-09-23 15:22:29
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Solar radiation exergy and quality performance for Iraq and Turkey
摘要： The present study is conducted with two primary objectives: First, a new formulation for the maximum efficiency of the solar radiation conversion is developed by considering the radiative energy transfer between two surfaces at different temperatures for a constant volume system. Second, a new methodology is introduced for estimating the exergy value of the monthly average daily horizontal global radiation, including many parameters, such as monthly average daily value of the horizontal extraterrestrial radiation, the number of sunny hours, the day length, the mean temperature and the mean wind velocity. Seven statistical parameters are used to validate the accuracy of all models. The results of the two new models are found to be more reliable than the results obtained from other models. This study, which was conducted for four locations in Iraq and Turkey. The findings would help in predicting the maximum availability of solar radiation based on weather parameters.
关键词： empirical models,solar radiation,solar radiation exergy
更新于2025-09-23 15:22:29
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UV-visible scanning spectrophotometry and chemometric analysis as tools for carotenoids analysis in cassava genotypes (Manihot esculenta Crantz)
摘要： In this study, the metabolomics characterization focusing on the carotenoid composition of ten cassava (Manihot esculenta) genotypes cultivated in southern Brazil by UV-visible scanning spectrophotometry and reverse phase-high performance liquid chromatography was performed. Cassava roots rich in β-carotene are an important staple food for populations with risk of vitamin A deficiency. Cassava genotypes with high pro-vitamin A activity have been identified as a strategy to reduce the prevalence of deficiency of this vitamin. The data set was used for the construction of a descriptive model by chemometric analysis. The genotypes of yellow-fleshed roots were clustered by the higher concentrations of cis-β-carotene and lutein. Inversely, cream-fleshed roots genotypes were grouped precisely due to their lower concentrations of these pigments, as samples rich in lycopene (red-fleshed) differed among the studied genotypes. The analytical approach (UV-Vis, HPLC, and chemometrics) used showed to be efficient for understanding the chemodiversity of cassava genotypes, allowing to classify them according to important features for human health and nutrition.
关键词： Chemometrics,cassava genotypes,partial metabolome,descriptive models,UV-vis,carotenoids,RP-HPLC
更新于2025-09-23 15:22:29