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Simulation and experimental study of the angle-dependent sensitivity of the thick pinhole used for gamma imaging
摘要： The angle-dependent sensitivity of rotationally symmetric thick pinholes used for gamma imaging was investigated using a geometric algorithm and Monte Carlo numerical simulations for the thick pinholes with different structural parameters. The effect of the pinhole diameter, the thickness of the straight-hole portion, and the half conical angle were analyzed. The point source was demonstrated to be a feasible replacement for the homogeneous plane source through theoretical deduction, numerical calculations, and experimental measurements of the angle-dependent sensitivity. A small quasi-point source was established based on a 10K curie level 60Co gamma ray source in the experimental measurement of the angle-dependent sensitivity. The image position remained unchanged and image distortion was avoided by rotating the thick pinhole around the pinhole center. The experimental result was in good agreement with the theoretical calculation, indicating the potential of this measurement method.
关键词： angle-dependent sensitivity,Monte Carlo method,quasi-point source,geometrical numerical algorithm,thick pinhole imaging
更新于2025-09-23 15:21:01
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Design, fabrication and characterization of a windowless extrapolation chamber for low-energy X-rays: Experimental and Monte Carlo results
摘要： Extrapolation chamber is a special parallel-plate ionization chamber, particularly suggested for low penetrating radiations. Its sensitive volume is varied through a change of the inter-electrode distance, ideally satisfying the Bragg-Gray cavity theory. A windowless extrapolation chamber was designed and constructed for low-energy X-rays, produced at the tube voltage of 70-100 kV. It consists of the following elements and innovation. The electrodes of the chamber are made of a homogenous block of graphite instead of a coating graphite layer to reduce the leakage current. Also, the entrance window has been eliminated to decrease the beam perturbation. To the best of our knowledge, this type of chamber has not been used in low energy X-rays before. The performance of the chamber was investigated in terms of its saturation curve, polarity effect, leakage current, linearity of response and short-term stability. It was also simulated using Monte Carlo method and in the worst case, the relative ionization current obtained in experiment differs about 4.5% with that in the simulation result. Moreover, the influence of chamber components on its response was examined. All of the results showed the feasibility of its use for detection of 70 - 100 kV X-rays.
关键词： simulation,Low-energy X-rays,Monte Carlo,Extrapolation chamber,dosimetry
更新于2025-09-23 15:21:01
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Few trapped quantum dipoles: quantum versus classical structures
摘要： We analyze the ground state of a two-dimensional quantum system of a few strongly con?ned dipolar bosons. Dipoles arrange in different stable structures that depend on the tilting polarization angle and the anisotropy of the con?ning trap. To this end, we use the exact diffusion Monte Carlo method and the quantum results are compared with classical ones obtained by stochastic optimization using simulated annealing. We establish the stability domains for the different patterns and estimate the transition boundaries delimiting them. Our results show signi?cant differences between the classical and quantum regimes which are mainly due to the quantum kinetic energy.
关键词： dipolar systems,Bose–Einstein condensation,quantum Monte Carlo,few-body physics
更新于2025-09-23 15:21:01
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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) - Sampling Technique for Defining Segmentation Error Margins with Application to Structural Brain Mri
摘要： Image segmentation is often considered a deterministic process with a single ground truth. Nevertheless, in practice, and in particular, when medical imaging analysis is considered, the extraction of regions of interest (ROIs) is ill-posed and the concept of 'most probable' segmentation is model-dependent. In this paper, a measure for segmentation uncertainty in the form of segmentation error margins is introduced. This measure provides a goodness quantity and allows a 'fully informed' comparison between extracted boundaries of related ROIs as well as more meaningful statistical analysis. The tool we present is based on a novel technique for segmentation sampling in the Fourier domain and Markov Chain Monte Carlo (MCMC). The method was applied to cortical and sub-cortical structure segmentation in MRI. Since the accuracy of segmentation error margins cannot be validated, we use receiver operating characteristic (ROC) curves to support the proposed method. Precision and recall scores with respect to expert annotations suggest this method as a promising tool for a variety of medical imaging applications including user-interactive segmentation, patient follow-up, and cross-sectional analysis.
关键词： Fourier domain,Segmentation uncertainty margins,sampling,MRI,Markov Chain Monte Carlo
更新于2025-09-23 15:21:01
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ANALYSIS OF MULTIPLICATION CHARACTERISTICS OF COAXIAL WAVEGUIDE LOADED CERAMIC UNDER EXTERNAL ELECTRIC FIELD
摘要： Multipacting is electron discharge that occurs in components operating in RF high-power electromagnetic fields. In this paper, we will study a new coaxial structure with a ceramic window. A similar structure is utilized in many high power devices for power transfer. Due to the multipactor effect, it will generate huge heat and cause damage to the window, ultimately affect the performance of microwave devices. In order to suppress the surface multipactor effect and improve the transmitting power, the application of an external DC bias is analyzed and simulated. A Monte Carlo algorithm is used to track the secondary electron trajectories and study the multipactor scenario on the surface of a ceramic window in a coaxial line by using 2-D particles distribution code. Since secondary electron multiplication needs to meet specific resonance conditions, an appropriate DC bias will generate a compensating trajectory and collision, which can suppress the secondary electron avalanche. The optimal value of this external bias voltage that will avoid the multipactor phenomenon in the coaxial line will be calculated by simulation in MATLAB.
关键词： DC bias,Coaxial waveguide,Monte Carlo simulation,Ceramic window,Multipacting
更新于2025-09-23 15:19:57
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Monte Carlo Simulation of Laser-Ablated Particle Splitting Dynamic in a Low Pressure Inert Gas
摘要： A Monte Carlo simulation method with an instantaneous density dependent mean-free-path of the ablated particles and the Ar gas is developed for investigating the transport dynamics of the laser-ablated particles in a low pressure inert gas. The ablated-particle density and velocity distributions are analyzed. The force distributions acting on the ablated particles are investigated. The in?uence of the substrate on the ablated-particle velocity distribution and the force distribution acting on the ablated particles are discussed. The Monte Carlo simulation results approximately agree with the experimental data at the pressure of 8 Pa to 17 Pa. This is helpful to investigate the gas phase nucleation and growth mechanism of nanoparticles.
关键词： Monte Carlo simulation,instantaneous mean-free-path,ablated particles,transport dynamic,low pressure
更新于2025-09-23 15:19:57
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Plasmonic Nanoslit Arrays Fabricated by Serial Bideposition: Optical and Surface-Enhanced Raman Scattering Study
摘要： Recently, studies have been carried out to combine surface-enhanced Raman spectroscopy substrates that are based on either localized surface plasmon or surface plasmon polariton structures. By combining these two systems, the individual drawbacks of each can be overcome. However, the manufacturing methods involved so far are sophisticated, labor-intensive, expensive, and technically demanding. We propose a facile method for the fabrication of a flexible plasmonic nanoslit SERS sensor. We utilized the pattern on periodic optical disks as an inexpensive substitute for printing the periodic pattern on polydimethylsiloxane with soft imprint lithography. The Ag nanoslits were fabricated by serial bideposition using the dynamic oblique angle deposition technique. The nanoslit structures were physically and optically characterized, and the experimental results were compared to the results of the numerical simulation: Monte Carlo and finite-difference time-domain simulation. The AgNS samples showed excellent SERS performance with an enhancement factor of ～105 and a limit of detection of 5 × 10-7 g/mL for a Rhodamine 6G solution. Their biosensing capability was demonstrated by the sensing of bilirubin.
关键词： FDTD,Ag nanoslit,Monte Carlo simulation,dynamic oblique angle deposition,SERS
更新于2025-09-23 15:19:57
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Enhancement of optical penetration depth of LED-based NIRS systems by comparing different beam profiles
摘要： Near-Infrared Spectroscopy (NIRS) is a non-invasive brain imaging technique involving the quantification of oxy and deoxy-hemoglobin concentrations resolved from the measurement of Near-Infrared (NIR) light attenuation within the tissue. Previous studies have shown that NIR light is more influenced by the optical properties of the superficial layers than those of the deeper target layers such as cortex. NIR light produced by the Laser source penetrates deeper regions of the tissue rather than the LED source although Laser needs more expensive instrumentation. In this study, we investigate the effect of Uniform and Gaussian beam profiles on the enhancement of LED light penetration depth. The latter beam profiles were generated and compared using Flat and Aspherical lenses applied to the LED sources. In order to increase the signal to noise ratio, the lenses were also applied to the light detector. For performance analysis, two experiments were carried out by scanning the intra space of a liquid phantom by static and dynamic (pulsating) absorbers. Monte Carlo simulations were also carried out to be compared with the experiment. The results showed that Gaussian beam profile and in particular, Bi-Convex lenses applied to both source and detector leads to a greater light penetration depth in the liquid phantom close to that of a Laser source.
关键词： near infrared spectroscopy,optical sensors,biomedical optic,monte carlo simulation,instrumentation
更新于2025-09-23 15:19:57
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[IEEE 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Chicago, IL, USA (2019.6.16-2019.6.21)] 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Monte Carlo Simulation of CdTe Thin Film Recrystallization Process During Chlorine Activation
摘要： In this paper we studied the grain growth and orientation change of CdTe multi-crystallize thin film during chlorine activation. A simulation of the chlorine activation process is also carried on by Monte-Carlo method combined with annealing algorithm based on thermodynamic energy criterion. Visualized pixel images of simulation are in good agreement with experimental results. Based on these results a thermodynamic energy criterion is proposed for finding non-toxic substitutes of cadmium chloride and predictions of substitutes are given.
关键词： Monte-Carlo simulation,CdCl2,CdTe,Cl treatment
更新于2025-09-23 15:19:57
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[IEEE 2019 25th International Workshop on Thermal Investigations of ICs and Systems (THERMINIC) - Lecco, Italy (2019.9.25-2019.9.27)] 2019 25th International Workshop on Thermal Investigations of ICs and Systems (THERMINIC) - Assessment of the validity of multi-domain LED model parameters in a broad current and temperature range
摘要： In this paper, a power switched, baseband modulation technique for visible light communications (VLC) is proposed and a theoretical model is constructed. It is shown that this technique, called single edge position modulation (SEPM), offers the unique performance characteristic that the communication properties reliability and power and spectral efficiency are invariable over a wide range of dimming levels. It is demonstrated that dimming robustness is obtained by increasing the number of bits per symbol. SEPM is compared with contemporary used baseband power switched modulation techniques for VLC that support dimming. The number of bits per symbol can be chosen to make a compromise between the dimming range over which reliability robustness is obtained on one hand, and the level of power and spectral efficiency on the other hand.
关键词： Modulation,visible light communications,reliability,Monte Carlo simulation,synchronization
更新于2025-09-23 15:19:57