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An interprojection sensor fusion approach to estimate blocked projection signal in synchronized moving grid-based CBCT system
摘要： Purpose: A preobject grid can reduce and correct scatter in cone beam computed tomography (CBCT). However, half of the signal in each projection is blocked by the grid. A synchronized moving grid (SMOG) has been proposed to acquire two complimentary projections at each gantry position and merge them into one complete projection. That approach, however, suffers from increased scanning time and the technical difficulty of accurately merging the two projections per gantry angle. Herein, the authors present a new SMOG approach which acquires a single projection per gantry angle, with complimentary grid patterns for any two adjacent projections, and use an interprojection sensor fusion (IPSF) technique to estimate the blocked signal in each projection. The method may have the additional benefit of reduced imaging dose due to the grid blocking half of the incident radiation. Methods: The IPSF considers multiple paired observations from two adjacent gantry angles as approximations of the blocked signal and uses a weighted least square regression of these observations to finally determine the blocked signal. The method was first tested with a simulated SMOG on a head phantom. The signal to noise ratio (SNR), which represents the difference of the recovered CBCT image to the original image without the SMOG, was used to evaluate the ability of the IPSF in recovering the missing signal. The IPSF approach was then tested using a Catphan phantom on a prototype SMOG assembly installed in a bench top CBCT system. Results: In the simulated SMOG experiment, the SNRs were increased from 15.1 and 12.7 dB to 35.6 and 28.9 dB comparing with a conventional interpolation method (inpainting method) for a projection and the reconstructed 3D image, respectively, suggesting that IPSF successfully recovered most of blocked signal. In the prototype SMOG experiment, the authors have successfully reconstructed a CBCT image using the IPSF-SMOG approach. The detailed geometric features in the Catphan phantom were mostly recovered according to visual evaluation. The scatter related artifacts, such as cupping artifacts, were almost completely removed. Conclusions: The IPSF-SMOG is promising in reducing scatter artifacts and improving image quality while reducing radiation dose.
关键词： moving grids,scatter correction,interpolation,sensor fusion,geometric model,SMOG,dose reduction,CBCT
更新于2025-09-23 15:22:29
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[ASME ASME 2018 International Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Microsystems - San Francisco, California, USA (Monday 27 August 2018)] ASME 2018 International Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Microsystems - Improved Approaches for FEA Analyses of PBGA Packages Subjected to Thermal Cycling
摘要： The study of solder joint reliability is one of the priority issues in electronic packaging. Solder alloys experience a highly nonlinear material behavior when subject to thermal cycling. It is a time consuming and difficult task to study the behavior of solder joints using experimental approaches. Finite element analysis provides a more efficient way to better understand the behavior of solder joints when accurate material models are available. With the developments of FEA algorithms and computer resources, the analysis approaches used for electronic packaging assemblies have evolved from 2-dimensional to 3-dimensional analyses, with far fewer assumptions needed in the fully 3D case. In this paper, we compare different FEA approaches covering various 2D and 3D modeling techniques to understand their advantages and drawbacks, especially as related to simulation accuracy and efficiency. Several models for a typical BGA assembly were prepared and analyzed including traditional mesh continuity models (2D slice model, 3D slice model, and 3D quarter model), as well as advanced models that employ Multi-Point Constraints (MPCs) and submodeling (global/local models). The Anand viscoplastic model was used for the solder joint material behavior in all of the FEA approaches. For the 3D mesh continuity models, an optimal analysis approach has been proposed to achieve the best balance between the accuracy of the simulation result and numerical efficiency of the simulation. Mesh transitions were used to maintain mesh continuity between regions of different mesh densities. A best choice of load step size was also found to reduce overall simulation time. For the analysis using MPCs to bond different meshes, two improved modeling strategies have been proposed including a suggested ratio of contacting elements and the use of multiple-MPC contact pairs to reduce overall mesh density of the FE model. An improved simulation strategy using submodeling has also been developed to obtain the best compromise in the global and local models between the mesh quality and load step size. An improved geometric simplification of the solder joint for use with energy based fatigue criteria was developed. Finally, comparisons and suggestions were made for the best analysis approach when using FEA techniques to predict the behavior of solder joints in PBGA packages.
关键词： 3D Model,Finite Element Analysis,PBGA,Multipoint Constraint,Submodeling,3D Slice Model,Global-Local Model,2D Slice Model
更新于2025-09-23 15:21:21
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Output field squeezing in a weakly-driven dissipative quantum Rabi model
摘要： We present a generalized method to address the squeezing spectrum of the output field for a weakly-driven, dissipative quantum Rabi model and calculate it for a range of coupling strengths covering strong, ultra-strong and deep-strong coupling regimes. The need for a generalization arises because of the periodic time dependence of the correlation functions due to counterrotating terms in the quantum Rabi model. We here adopt time-averaging over such correlation functions to obtain the squeezing spectrum, which may also be relevant to experimental situations. We compare the calculated squeezing spectra with those of the driven dissipative Jaynes-Cummings model to illustrate the departure from the latter as the interaction strength increases. Our calculation shows that the overall squeezing increases with the interaction strength after optimization over the system-bath coupling strength and the driving field strength.
关键词： Quantum Rabi model,Jaynes-Cummings model,Spectrum of squeezing
更新于2025-09-23 15:21:21
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Photocatalytic Degradation of Anthracene in Aqueous Dispersion of Metal Oxides Nanoparticles: Effect of Different Parameters
摘要： Contamination with anthracene, as one of polycyclic aromatic hydrocarbons (PAHs), was considered as an important health issue due to its carcinogenic and mutagenic activity. In this paper, we focused on the photocatalytic degradation of anthracene in different media and in presence of various photocatalysts. Zinc oxide nanoparticles (ZnO NPs) and nickel oxide nanoparticles (NiO NPs) were prepared and utilized as efficient photocatalysts to convert anthracene into safer compounds. The as-prepared photocatalysts were characterized by x-ray diffraction (XRD), transmission electron microscopy (TEM) and UV-VIS spectroscopy. The factors affecting the efficiency of photocatalytic degradation, including irradiation time, loading catalyst doses, pH value and H2O2 as an oxidizing agent, were investigated. The optimum photocatalytic degradation of 23 mg/L anthracene in different media was carried out at pH 7.2 with loading catalyst dose of 55.6 mg/L. In case of anthracene emulsion solution, a faster photochemical kinetic was observed in presence of ZnO NPs and more than 90% of photocatalytic degradation percentage was reached in 230 min. However, in case of anthracene aqueous solution and in presence of ZnO NPs/H2O2, a degradation efficiency of 84 % was obtained within 50 min. The byproducts of 4- formyl-benzoic acid ethyl ester (98.23%) and 1,2-Benzenedicarboxylic acid, isopropyl methyl ester (0.85%)) were detected by gas chromatography-mass spectrometry (GC-MS). The kinetic studies were achieved and revealed that the photocatalytic degradation process obeyed a Langmuir–Hinshelwood model and followed a pseudo-first order rate expression.
关键词： Pseudo-first order,Langmuir–Hinshelwood model,Anthracene,Metal oxide nanoparticles,Photocatalysis
更新于2025-09-23 15:21:21
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Phase field modeling of grain boundary migration and preferential grain growth driven by electric current stressing
摘要： A phase field model incorporating the electrostatic free energy and the grain orientation effect is developed and employed to study the grain boundary migration and preferential grain growth in widely used beta-tin (β-Sn) under electric current stressing. The directional migration of grain boundaries and the preferential growth of the grain with its orientation having low electrical resistivity along the electric current direction are theoretically clarified. In a bicrystal system containing a circular grain, the shrinkage velocity and morphology changes of grains are dominated by the competition effect between the grain boundary energy and the electrostatic free energy; in particular, the high-density electric current can induce the instability of grain morphology evolution. Moreover, grain morphology evolution leads to the change of the voltage across the β-Sn system; it is found that the voltage decreases over time in a tricrystal system, while the variation of the voltage across the bicrystal system is related to the above-mentioned competition effect. The proposed model and results provide insights into the orientation-related microstructure evolution under electric current stressing.
关键词： preferential grain growth,electric current stressing,microstructure evolution,grain boundary migration,beta-tin,phase field model
更新于2025-09-23 15:21:21
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A theoretical investigation of the glide dislocations in the sphalerite ZnS
摘要： The 90(cid:1) and 30(cid:1) partial glide dislocations in ZnS are investigated theoretically in the framework of the fully discrete Peierls model and first-principles calculation. It is found that there are four types of equilibrium cores for each kind of partial glide dislocation, which are named as the O-Zn-core, the B-Zn-core, the O-S-core, and the B-S-core, according to their geometrical feature and atomic ingredient at the core. For the 90(cid:1) partial dislocation, the O-Zn-core (double-period core) and the B-S-core (single-period core) are stable. The Peierls barrier heights of the O-Zn-core and the B-S-core are about 0:03 eV/? and 0:01 eV/?, respectively. For the 30(cid:1) partial dislocation, the O-Zn-core (double-period core) and the B-Zn-core (single-period core) are stable and their Peierls barrier heights are approximately the same as that of the O-Zn-core of the 90(cid:1) partial dislocation. The Peierls stress related to the barrier height is about 800 MPa for the 90(cid:1) partial dislocation with the B-S-core. The existence of unstable equilibrium cores enables us to introduce the concept of the partial kink. Based on the concept of the partial kink, a minimum energy path is proposed for the formation and migration of kinks. It is noticed that the step length in kink migration is doubled due to the core reconstruction.
关键词： glide dislocations,sphalerite ZnS,Peierls model,partial kink,first-principles calculation
更新于2025-09-23 15:21:21
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Fluorene – Triazine Conjugated Porous Organic Polymer Framework for Superamplified Sensing of Nitroaromatic Explosives
摘要： A porous organic polymer with fluorene and triazine units (PTF), was synthesised through a simple cost effective method. The material was well characterised by FT-IR, solid state 13C NMR and X-ray photoelectron spectroscopic studies. Absorption spectrum indicated the electronic coupling between the two units in the polymer backbone. Experiments proved high thermal and chemical stability, and porous nature of the material. Luminescence of PTF was quenched, on the addition of ppb level concentration of nitroaromatic compounds. This was attributed to the photo induced electron transfer from the electron rich polymer backbone to the electron deficient nitro aromatic compounds. The observed superamplification effect in the fluorescence quenching was studied extensively by a series of ground state absorption, steady state and time resolved fluorescence experiments. Finally, the superamplified quenching was successfully assigned to static quenching by quenching sphere of action model. High value of static quenching constant of the order of 3.9 × 103 M-1, for picric acid combined with detection limit as low as 89 ppb envisages PTF as an effective chemosensor for nitroaromatic explosives.
关键词： sphere of action model,porous polymer,fluorescence life-time,Stern-Volmer plot,cyanuric chloride,fluorescence quenching
更新于2025-09-23 15:21:21
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orbitals in two-dimensional regular optical lattices
摘要： In solids, crystal field splitting refers to the lifting of atomic orbital degeneracy by the surrounding ions through the static electric field. Similarly, we show that the degenerated d orbitals, which were derived in the harmonic oscillator approximation, are split into a low-lying dx2+y2 singlet and a dx2?y2/xy doublet by the high-order Taylor polynomials of triangular optical potential. The low-energy effective theory of the orbital Mott insulator at 2/3 filling is generically described by the Heisenberg-compass model, where the antiferro-orbital exchange interactions of compass type depend on the bond orientation and are geometrically frustrated in the triangular lattice. While, for the square optical lattice, the degenerated d orbitals are split into a different multiplet structure, i.e., a low-lying dx2±y2 doublet and a dxy singlet, which has its physical origin in the C4v point group symmetry of square optical potential. Our results build a bridge between ultracold atom systems and solid-state systems for the investigation of d-orbital physics.
关键词： orbital Mott insulator,Heisenberg-compass model,crystalline splitting,d orbitals,optical lattices
更新于2025-09-23 15:21:21
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Rapid holographic phase transition with brane-localized curvature
摘要： We study the finite-temperature properties of the Randall-Sundrum model in the presence of brane-localized curvature. At high temperature, as dictated by AdS=CFT, the theory is in a confined phase dual to the planar anti-de Sitter black hole. When the radion is stabilized, á la Goldberger-Wise, a holographic first-order phase transition proceeds. The brane-localized curvature contributes to the radion kinetic energy, which allows us to substantially decrease the critical bubble energy. Contrary to previous results, the phase transition is completed at much larger values of N, the number of degrees of freedom in the conformal field theory. Moreover, the value of the bulk scalar on the TeV brane is allowed to become large, consistent with backreaction constraints. Assisted by this fact, we find that for a wide region in the parameter space tunneling happens rather quickly, i.e., Tn=Tc ～ Oe0.1–1T. At zero temperature, the most important signature of brane-localized curvature is the reduction of spin-2 Kaluza-Klein graviton masses and a heavier radion.
关键词： holographic phase transition,Kaluza-Klein graviton,brane-localized curvature,radion,Randall-Sundrum model
更新于2025-09-23 15:21:21
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[IEEE 2018 25th IEEE International Conference on Image Processing (ICIP) - Athens, Greece (2018.10.7-2018.10.10)] 2018 25th IEEE International Conference on Image Processing (ICIP) - A Machine Learning Approach to Accurate Sequence-Level Rate Control Scheme for Video Coding
摘要： In this paper, we propose a two-pass encoding framework to handle the problem of sequence-level rate control. We consider the sequence-level encoding parameter constant rate factor (CRF) as the factor to be adjusted. The proposed framework mainly has two key contributions. First, we provide a second order model to characterize the relationship between the bitrate and CRF. The proposed second order model outperforms the traditional linear model significantly. Second, we adopt a shallow neural network to train the relationship between the content-dependent features with the second-order model parameters. The proposed neural network is quite simple but able to estimate the model parameters accurately. We implement the proposed algorithm under tensorflow. Experimental results show that our proposed method obviously outperforms the state-of-the-art method.
关键词： sequence-level,constant rate factor,video coding,Rate control,Machine learning,second order model
更新于2025-09-23 15:21:21