Mitra Ghergherehchi

A NEURO-FUZZY BASED MODEL FOR ACCURATE ESTIMATION OF THE LYAPUNOV EXPONENTS OF AN UNKNOWN DYNAMICAL SYSTEM

A neuro-fuzzy based model is proposed in this paper for estimating the Lyapunov exponents of an unknown dynamical system according solely to a set of observations. Several approaches have been presented in recent years; most of them using the approximation of both the function of the trajectory of observations and the partial derivatives, to yield the Jacobian matrix of the function. The Jacobian matrix is then employed in the Jacobian-based methods that extract the Lyapunov exponents by QR-decomposition. While the accurate estimation of Lyapunov exponents has been sought, most of the related papers mainly focus on the accuracy of the trajectory approximation. In this paper, an Adaptive Neuro-Fuzzy Inference System is presented and stated to be an efficient tool for such a purpose. Structural parameters of the proposed model as the embedding dimension and the delay time are calculated by the Takens theorem and autocorrelation function, respectively. Model validation is performed by cross approximate entropy. Then, the promising performance of the proposed model as an accurate estimation of the Lyapunov exponents and its robustness to the measurement noise are finally evaluated.

Estimation of photoneutron yield in linear accelerator with different collimation systems by Geant4 and MCNPX simulation codes

At present, the bremsstrahlung photon beams produced by linear accelerators are the most commonly employed method of radiotherapy for tumor treatments. A photoneutron source based on three different energies (6, 10 and 15 MeV) of a linac electron beam was designed by means of Geant4 and Monte Carlo N-Particle eXtended (MCNPX) simulation codes. To obtain maximum neutron yield, two arrangements for the photo neutron convertor were studied: (a) without a collimator, and (b) placement of the convertor after the collimator. The maximum photon intensities in tungsten were 0.73, 1.24 and 2.07 photon/e at 6, 10 and 15 MeV, respectively. There was no considerable increase in the photon fluence spectra from 6 to 15 MeV at the optimum thickness between 0.8 mm and 2 mm of tungsten. The optimum dimensions of the collimator were determined to be a length of 140 mm with an aperture of 5 mm  ×  70 mm for iron in a slit shape. According to the neutron yield, the best thickness obtained for the studied materials was 30 mm. The number of neutrons generated in BeO achieved the maximum value at 6 MeV, unlike that in Be, where the highest number of neutrons was observed at 15 MeV. Statistical uncertainty in all simulations was less than 0.3% and 0.05% for MCNPX and the standard electromagnetic (EM) physics packages of Geant4, respectively. Differences among spectra in various regions are due to various cross-section and stopping power data and different simulations of the physics processes.

Monte Carlo study of neutron-ambient dose equivalent to patient in treatment room.

This paper presents an analytical method for the calculation of the neutron ambient dose equivalent H* (10) regarding patients, whereby the different concrete types that are used in the surrounding walls of the treatment room are considered. This work has been performed according to a detailed simulation of the Varian 2300C/D linear accelerator head that is operated at 18MV, and silver activation counter as a neutron detector, for which the Monte Carlo MCNPX 2.6 code is used, with and without the treatment room walls. The results show that, when compared to the neutrons that leak from the LINAC, both the scattered and thermal neutrons are the major factors that comprise the out-of field neutron dose. The scattering factors for the limonite-steel, magnetite-steel, and ordinary concretes have been calculated as 0.91±0.09, 1.08±0.10, and 0.371±0.01, respectively, while the corresponding thermal factors are 34.22±3.84, 23.44±1.62, and 52.28±1.99, respectively (both the scattering and thermal factors are for the isocenter region); moreover, the treatment room is composed of magnetite-steel and limonite-steel concretes, so the neutron doses to the patient are 1.79 times and 1.62 times greater than that from an ordinary concrete composition. The results also confirm that the scattering and thermal factors do not depend on the details of the chosen linear accelerator head model. It is anticipated that the results of the present work will be of great interest to the manufacturers of medical linear accelerators.

Modification on chemical and optical properties of PADC polymer by ArF laser (193 nm) irradiation

Abstract Poly allyl diglycol carbonate (PADC) has been irradiated by ArF(UV)-laser light (wavelength 193 nm) at different fluences and pulse numbers in order to investigate the photo degradation of chemical molecular structure. The photo-induced chemical reactions and photo-degradation mechanism at the irradiated polymer surface have been clarified by ultraviolet-visible (UV-Vis) spectrum and FTIR spectrum analyses. Optical and surface modifications of irradiated samples have been studied by refractive index and water contact angle measurements. Using the UV-Vis spectra, Urbach’s energy (Eu), indirect and direct band gaps energy (Eg) of unirradiated and UV-laser irradiated samples were determined. The UV-Vis and FTIR spectra analysis show that photo degradation and photo oxidation of polymer caused free-radical generation. In the presence of air, free-radical generation induced by UV-laser light followed by bond scission and cross-linking process will finally produce new products. New product generation can be affected on chemical and optical properties of irradiated samples. The irradiated PADC at various fluences in the range of medium to high demonstrate improvement of refractive index, and this is highly important in plastic lens technology. The obtained results reveal that chemical modification could affect track parameters when PADC is used as a nuclear track detector.

RANdom sample consensus (RANSAC) algorithm for enhancing overlapped etched track counting

In this study, a method to enhance the accuracy of overlapped etched track analysis is proposed. Counting tracks by eye is not an easy task and automated tracks counting systems are attractive key for this problem. This method supplements the deficiencies of the conventional track analysis method. A computer programme named KoreaTech Track Measurement System written in C++, which is the authors’ previous method, has been upgraded. In the proposed track analysis method, the track images captured from solid state nuclear track detectors are geometrically analysed and the number of tracks is counted. A damaged etching track shape can be restored on the track image to improve the analysis accuracy. For track restoration, the effective points are differentiated from the damaged track image. The track image is then restored by estimating the radii (small object removal) or their axis (ellipse, circle and non-circle) using the RANdom sample consensus method. Using the restored track image, the track parameters are obtained from the ellipse and then approximated to the contour of the track image to analyse the track image. Then, the total number of tracks including the overlapped tracks is counted. To verify the proposed track analysis method, experiments using actual etching track images are conducted and the results are discussed.

Ablation and cone formation mechanism on CR-39 by ArF laser irradiation

In this work, chemical properties, surface modification, and micro structures formation on ablated polyallyl di-glycol carbonate (CR-39) polymer by ArF laser irradiation (λ = 193 nm) at various fluences and pulse number were investigated. CR-39 samples have been irradiated with an ArF laser (193 nm) at a repetition rate of 1 Hz. Threshold fluence of ablation and effective absorption coefficient of CR-39 were determined. Conical microstructures (Taylor cone) formed on laser-ablated CR-39 exhibit: smooth, Taylor cone shape walls and sharp tips together with interference and well defined fringe-structure with a period of 230 nm, around cone base. Mechanism of cone formation and cone evolution of CR-39 ablated surface were investigated by change of fluences (at a given pulse number) and pulse number (at a given fluence). Cone height, cone base, and region of interface were increased in micrometer steps by increasing the total fluence. Depression on the base of the cone and the circular fringe were simulated. FTIR spectra were measured and energy dispersive x-ray analysis of irradiated and un-irradiated samples was performed.

Design of Control System for Dual-Head Radiation Therapy

Sungkyunkwan University groups have been developed advanced radiation therapy machine named dual-head radiation therapy gantry for reducing the treatment time by up to 30%. The main difference between previous radiation therapy machine [1] is using two electron LINAC as X-ray sources at radiation therapy. In support of this system, control system based on SCADA and hardware development was implemented. The control system consists of supervisory computers and local controllers and the control network was ethernet and software was written by labVIEW. An overview of this control system is presented in paper. INTRODUCTION Sungkyunkwan University has developed a dual head radiation therapy system since 2012, which is a radiation therapy system that aims to reduce treatment time up to 30% than conventional radiation therapy machine [2]. To reduce treatment time, dual X-ray source, head are equipped with this system. developed dual-head gantry system is shown in Fig. 1. Those system configurations have economic benefits and advantages on account of reducing radiation treatment time but the additional installation of components result in space limit and a complexity of the system. To overcome space limit, we use 6 MeV Xband LINAC as X-ray source and it sufficiently reduce not only cavity volume but also waveguide and magnetron [3]. Controlling dual X-ray source is new challenge. in contrast to conventional TomoTherapy that use single X-ray source, dual head gantry system uses dual X-ray sources ssimultaneously or sequentially so control system requires supervisory control and sequence control that not only include data acquisition and monitoring but also two electron LINAC beam pulse synchronization. Figure 1: Dual-head Radiation therapy system. SYSTEM HARDWARE CONFIGURATION Developed gantry system is consist of subsystems such as two heads, electron LINAC and gantry robot and subsystems have each local controller. Head subsystem objective is to control the radiation path from the LINAC to the patient. It measures radiation dose rate and control X-ray field size. Its appearance is shown in Fig. 2 Head’s main control unit is Atmega2560 and control board has potential meters and limit switches for interlock. Figure 2: Gantry Head Appearance. Five motors in head system have each driver. By using daisy-chain scheme, master motor manages other slave motors as shown in Fig. 3. Figure 3: Gantry head system block diagram. 9th International Particle Accelerator Conference IPAC2018, Vancouver, BC, Canada JACoW Publishing ISBN: 978-3-95450-184-7 doi:10.18429/JACoW-IPAC2018-THPML076

Development of a disposable kit with fully automatic self-shielding reactor for [18F]FDG synthesis

A self-shielding device for the synthesis of radiopharmaceuticals was developed and fabricated in this study. Radiation exposure was minimized by the self-shielding of the kit, installation of the disposable kit in the auxiliary chamber while in a shielded state, and discharge of the kit into a radioactive waste container upon completion of the synthesis process. The developed self-shielding synthesis kit was tested by synthesizing 2-[18F]fluoro-2-deoxy-D-glucose ([18F]FDG) in order to verify its performance.

Development of an 83.2 MHz, 3.2 kW solid-state RF amplifier using Wilkinson power divider and combiner for a 10 MeV cyclotron

We design a stripline-type Wilkinson power divider and combiner for a 3.2 kW solid-state radio frequency (RF) amplifier module and optimize this setup. A Teflon-based printed circuit board is used in the power combiner to transmit high RF power efficiently in the limited space. The reflection coefficient (S11) and insertion loss (S21) related to impedance matching are characterized to determine the optimization process. The resulting two-way divider reflection coefficient and insertion loss were -48.00 dB and -3.22 dB, respectively. The two-way power combiner reflection coefficient and insertion loss were -20 dB and -3.3 dB, respectively. Moreover, the 3.2 kW solid-state RF power test results demonstrate that the proposed power divider and combiner exhibit a maximum efficiency value of 71.3% (combiner loss 5%) at 48 V supply voltage.

Development of new 116Cd/Pt target for cyclotron produced 117mSn as a medical radiometal

The radioisotope 117mSn has recently attracted considerable attention because of its application in theranostics and its imaging using 159-keV γ-photons. In this study, we developed a target system that yielded 117mSn via a 116Cd(α, 3n)117mSn nuclear reaction. A separable Pt substrate was utilized to prepare the enriched 116Cd target to be irradiated, and the enriched 116Cd in a cadmium acetate solution was electroplated onto the Pt substrate. The substrate was thermally analyzed via ANSYS simulations, and the plating thickness was optimized through calculations with TALYS code. The production of 117mSn was confirmed through the emission measurement of inherent gamma rays.