Examinando por Autor "Davis, S."
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Ítem A portable and flexible implementation of the Wang–Landau algorithm in order to determine the density of states(Elsevier B.V., 2022-01) Moreno, F.; Davis, S.; Peralta, J.In this work we develop an implementation of the Wang–Landau algorithm Wang and Landau (2001) [4]arXiv e-prints. This algorithm allows us to find the density of states (DOS), a function that, for a given system, describes the proportion of states that have a certain energy. The implementation uses the Python and C++ languages for the algorithm itself, and it can take advantage of any library, such as the powerful LAMMPS library, for the computation of energy. Therefore, the resulting implementation is simple and flexible without sacrificing efficiency. This implementation also considers recent developments in the parallelization of the code for faster computation. We establish the soundness and effectiveness of our implementation by studying well-known systems such as the Ising model, the Lennard–Jones and EAM solids. We have found that our implementation can find the DOS with very good precision in a reasonable amount of time. Therefore, we are equipped with a very powerful and flexible implementation that can be easily used in order to study more realistic models of matter. Program summary: Program Title: Republica Wang–Landau (RWL) CPC Library link to program files: https://doi.org/10.17632/gcx9k8wnhh.1 Licensing provisions: GPLv3 Programming language: Python, C++ Nature of problem: An implementation of the WL algorithm that is flexible enough to be used for a large variety of systems. Solution method: This implementation separates the actual Wang–Landau code of the abstract implementation of the system. Therefore, any system can be attached as a walker—a Python class that represents the system.Ítem Analysis of Deterioration in a Plasma Focus Device(Institute of Physics Publishing, 2018-06) Zanelli, D.; López, E.; Pavez, C.; Pedreros, J.; Jain, J.; Avaria, G.; Moreno, J.; Bora, B.; Davis, S.; Soto, L.The Plasma Focus (PF) is a kind of dense transient plasmas in with high-pulsed voltage. To produce devices for eld application it is necessary to obtain PF equipment able to operate for a long period of time. Thus, a reliability analysis is indispensable. In this work a reliability analysis program for plasma focus devices is presented. The program considers a criticality analysis using Failure Modes and Effects Criticality Analysis (FMECA) to identify the most important failure modes of the system. Said failure modes are studied operating the Plasma Focus for many cycles, obtaining from them the characteristic curves of V(t) and İ(t). Feature Extraction (FE) techniques are applied to obtain a list of parameters that correlate to the degrading process. Furthermore, Machine Learning tools are used to learn from the obtained data, linking the changes in these parameters during its life cycle to the decay of the system in hope for future implementation of a predictive maintenance system and a reference for data analysis and prediction in PFs. The study was applied to a portable plasma focus device operated at 2 joules of stored energy. © Published under licence by IOP Publishing Ltd.Ítem Bayesian inference of spectrometric data and validation with numerical simulations of plasma sheath diagnostics of a plasma focus discharge(Nature Research, 2022-09) Avaria, G.; Clausse, A.; Davis, S.; Pavez, C.; Villalba, N.; Cuadrado, O.; Moreno, J.; Ruiz, M.; Soto, L.Plasma Foci are pulsed coaxial discharges with numerous radiation applications and interesting scientific phenomena. Although the physics answered much of the processes involved in these discharges, many related fundamental questions still remains doggedly unresolved. One of the obstacles to deeper knowledge is the scarcity of reliable experimental data. This work presents an elaborate experimental assessment of the electron density in the rundown phase of a 400 J Plasma Focus operating with hydrogen. The rundown of the plasma sheath is basically a hypersonic shock wave between two coaxial electrodes accelerated by the Lorentz force, and it is important to control the pinch formation. The electron density of the passing sheath is measured by means of the Stark broadened hydrogen alpha emission with spatial and temporal resolution. The experimental data is post-processed using Bayesian posterior probability assessment. The results are conflated with the numerical model CShock to construe an educated explanation of the sheath behavior during the rundown. In particular, it is possible to reckon the formation of a toroidal instability reported in previous experiments, and to estimate the plasma sheath temperature (4–20 eV) and velocity (62.5 km/s) at this stage.Ítem Deterministic physical systems under uncertain initial conditions: the case of maximum entropy applied to projectile motion(Institute of Physics Publishing, 2018-05) Montecinos, A.; Davis, S.; Peralta, J.The kinematics and dynamics of deterministic physical systems have been a foundation of our understanding of the world since Galileo and Newton. For real systems, however, uncertainty is largely present via external forces such as friction or lack of precise knowledge about the initial conditions of the system. In this work we focus on the latter case and describe the use of inference methodologies in solving the statistical properties of classical systems subject to uncertain initial conditions. In particular we describe the application of the formalism of maximum entropy (MaxEnt) inference to the problem of projectile motion, given information about the average horizontal range over many realizations. By using MaxEnt we can invert the problem and use the provided information on the average range to reduce the original uncertainty in the initial conditions. Also, additional insight into the initial condition's probabilities, and the projectile path distribution itself, can be achieved based on the value of the average horizontal range. The wide applicability of this procedure, as well as its ease of use, reveals a useful tool with which to revisit a large number of physics problems, from classrooms to frontier research. © 2018 European Physical Society.Ítem Experimental measurements of high-energy photons in X-rays pulses emitted from a hundred joules plasma focus device and its interpretations(Elsevier, 2020-03) Jain, J.; Moreno, J.; Davis, S.; Bora, B.; Pavez, C.; Avaria, G,; Soto, L.In the present work, efforts are made to identify the presence of high energy photons in X-rays pulses, emitted from a hundred joules plasma focus device, PF-400J. Two different experiments were carried out, with the insertion of a lead piece inside the hollow anode of PF-400J and without insertion of the lead piece. A pair of two photomultiplier tubes (PMTs) was mounted in the axial direction and a similar pair of PMTs was mounted in the radial direction, simultaneously. After establishing a correlation between two PMTs in each pair, one of the PMTs in both directions was blocked by a rectangular slab of the lead of thickness ~17 mm. Linear attenuation coefficient (LAC) of lead was estimated using the PMTs signals. Later, the X-rays energies were interpolated for the estimated LAC values in both cases, with and without insertion of lead piece inside the hollow anode. Interpolated energies reveal the presence of 0.55–0.85 MeV photons in the X-rays pulses in the axial direction, while, in radial direction ranges 0.4–0.9 MeV, for the case without lead inserted inside the hollow anode. Insertion of the lead inside the hollow anode does not change the X-rays energies significantly, nonetheless, it increases X-rays repetition rate per hundred discharges. The presence of high energy photons in the X-rays pulses indicates the existence of relativistic electrons. To explain it, induced electric and magnetic fields were estimated using generalized Ohm’s law. We conclude that the electron acceleration mechanisms might not be the same in the axial and radial directions.Ítem Hundred joules plasma focus device as a potential pulsed source for in vitro cancer cell irradiation(American Institute of Physics Inc., 2017-08) Jain, J.; Moreno, J.; Andaur, R.; Armisen, R.; Morales, D.; Marcelain, K.; Avaria, G.; Bora, B.; Davis, S.; Pavez, C.; Soto, L.Plasma focus devices may arise as useful source to perform experiments aimed to study the effects of pulsed radiation on human cells in vitro. In the present work, a table top hundred joules plasma focus device, namely "PF-400J", was adapted to irradiate colorectal cancer cell line, DLD-1. For pulsed x-rays, the doses (energy absorbed per unit mass, measured in Gy) were measured using thermoluminescence detectors (TLD-100 dosimeters). The neutron fluence and the average energy were used to estimate the pulsed neutron doses. Fifty pulses of x-rays (0.12 Gy) and fifty pulses of neutrons (3.5 μGy) were used to irradiate the cancer cells. Irradiation-induced DNA damage and cell death were assessed at different time points after irradiation. Cell death was observed using pulsed neutron irradiation, at ultralow doses. Our results indicate that the PF-400J can be used for in vitro assessment of the effect of pulsed radiation in cancer cell research.Ítem Inference of X-Ray Emission from a Plasma Focus Discharge: Comparison between Characteristic Parameters and Neural Network Analyses(Institute of Electrical and Electronics Engineers Inc., 2020) Orellana, L.; Avaria, G.; Ardila-Rey, J.; Davis, S.; Schurch, R.; Pavez, C.Pulsed plasma discharges, such as the plasma focus, are a source of pulsed X rays, therefore it is desirable to understand the relationship between this fast transient phenomena and the electrical variables of the discharge. Parameters from the electrical diagnostic signals are typically used to characterize the plasma focus discharge and for the correlations with X rays measurements via scatter plots. To further evaluate relevant information in the electrical signals, besides the characteristic parameters, an implementation of different types of machine learning algorithms, that included deep learning, was performed. A classification of pulses associated with an X rays measurement, in terms of the electrical signals data as input, was carried out. Two approaches were compared: the selection of the characteristic parameters and the use of the entire signals so the algorithms could find additional information for the classification task. The electrical diagnostic signals corresponded to: the voltage at the electrodes of the discharge chamber measured with a resistive voltage divider; time variation of the circuit current measured with a Rogowski coil and an inductive loop sensor; and the electromagnetic burst from the circuit measured with a Vivaldi antenna. The X rays measurement corresponded to the signal obtained from a scintillator-photomultiplier. In terms of the performance of the algorithms models in this classification problem, the results indicated that there is no significative improvements when using the entire signal or the selection of characteristic parameters. The best results were obtained when the following parameters were used: voltage at time of gas breakdown, voltage at time of pinch, current at time of pinch, time derivative of current at time of pinch, time from breakdown to pinch, and the Fast Fourier Transform of the part of the Vivaldi antenna signal related to the pinch event.Ítem Probabilistic inference for dynamical systems(MDPI AG, 2018-09) Davis, S.; González, D.; Gutiérrez, G.A general framework for inference in dynamical systems is described, based on the language of Bayesian probability theory and making use of the maximum entropy principle. Taking the concept of a path as fundamental, the continuity equation and Cauchy's equation for fluid dynamics arise naturally, while the specific information about the system can be included using the maximum caliber (or maximum path entropy) principle. © 2018 by the authors.Ítem Pulsed x-rays dose measurements from a hundred joules plasma focus device(Institute of Physics Publishing, 2018-06) Jain, J.; Moreno, J.; Avila, R.E.; Avaria, G.; Pavez, C.; Bora, B.; Davis, S.; Soto, L.Present work is aimed to perform dosimetric measurements to characterize dosis obtained from pulsed x-rays emitted from a hundred joules plasma focus device PF-400J using thermoluminescent dosimeters (TLD-100). Two dosimeter arrays (containing 21 dosimeters in each) were used. One of the arrays was kept inside the PF-400J vacuum chamber and other outside the vacuum chamber, simultaneously. It was found that dosis obtained from the inside array (∼200.7 mGy) were hundred times larger than the outside array (∼1.1 mGy) for hundred pulses of x-rays. Later, the vacuum window of PF-400J, which was made of 1 mm aluminum, was replaced by a plastic window and a similar dosimeter array was kept outside the chamber over the plastic window. With this arrangement, the obtained doses (100 pulses of x-rays) were of the same order of magnitude (∼106 mGy) as it was inside the vacuum chamber. Later, a lead piece was inserted inside the hollow anode of PF-400J, which increased dose (∼250 mGy) per hundred pulses of x-ray outside the vacuum chamber using plastic vacuum window. Our results suggest that PF-400J could be a useful device to study low dose pulsed radiation effects on cancer cell lines in in vitro experiments. © Published under licence by IOP Publishing Ltd.Ítem Ti film deposition process of a plasma focus: Study by an experimental design(American Institute of Physics Inc., 2017-10) Inestrosa-Izurieta, M.J.; Moreno, J.; Davis, S.; Soto, L.The plasma generated by plasma focus (PF) devices have substantially different physical characteristics from another plasma, energetic ions and electrons, compared with conventional plasma devices used for plasma nanofabrication, offering new and unique opportunities in the processing and synthesis of Nanomaterials. This article presents the use of a plasma focus of tens of joules, PF-50J, for the deposition of materials sprayed from the anode by the plasma dynamics in the axial direction. This work focuses on the determination of the most significant effects of the technological parameters of the system on the obtained depositions through the use of a statistical experimental design. The results allow us to give a qualitative understanding of the Ti film deposition process in our PF device depending on four different events provoked by the plasma dynamics: i) an electric erosion of the outer material of the anode; ii) substrate ablation generating an interlayer; iii) electron beam deposition of material from the center of the anode; iv) heat load provoking clustering or even melting of the deposition surface.