Electrical nerve fiber stimulation is a technique widely used in prosthetics and rehabilitation, and its study from a computational point of view can be a useful instrument to support experimental ...tests. In the last years, there was an increasing interest in computational modeling of neural cells and numerical simulations on nerve fibers stimulation because of its usefulness in forecasting the effect of electrical current stimuli delivered to tissues through implanted electrodes, in the design of optimal stimulus waveforms based on the specific application (i.e., inducing limb movements, sensory feedback or physiological function restoring), and in the evaluation of the current stimuli properties according to the characteristics of the nerves surrounding tissue. Therefore, a review study on the main modeling and computational frameworks adopted to investigate peripheral nerve stimulation is an important instrument to support and drive future research works. To this aim, this paper deals with mathematical models of neural cells with a detailed description of ion channels and numerical simulations using finite element methods to describe the dynamics of electrical stimulation by implanted electrodes in peripheral nerve fibers. In particular, we evaluate different nerve cell models considering different ion channels present in neurons and provide a guideline on multiscale numerical simulations of electrical nerve fibers stimulation.
Abstract
The present work is focused on the characterization of a
Timepix3 (TPX3) based test system for the identification of
particles produced by the complex decay chain of
222
Rn. The
detector ...used is composed of a pixelated Cadmium Telluride (CdTe)
semiconductor (500 μm thick) bump-bonded on an ASIC TPX3
chip. Measurements were carried out at the NIXT Laboratory (ENEA
Frascati) using radioactive sources and exploiting the presence of
natural radon gas by collecting its decay products on the sensor
surface. Estimation of the radon gas risk is one of the most
important problems in radiation protection and has stimulated
further development of new advanced methods suitable for detecting
this gas in confined environments. A study of the spatial uniformity
and high energy calibration is also presented and an improved
cluster analysis is introduced. The performance highlighted in this
study will allow a detailed and faster analysis of the radon
products and may have an important impact on the environmental
radioprotection applications. This paper describes the application
and use of this test system to identify the different decay
signatures and follow the temporal evolution of the Radon decay
chain.
The particular physics of Laser Produced Plasmas (LPP) needs some diagnostic requirements. Specifically, the X-ray monitoring of the plasma is known to be difficult since typically X-ray emissions ...are concentrated in bursts from a few tens of ps to few ns, based on the power and pulse time width of the laser. Therefore, the energy measurement of the radiation coming from a single experimental run is basically unfeasible using conventional techniques. Additional particles can be produced from LPP experiments, especially high energy gamma photons and electrons. As a case study in recent experiments, carried out on VEGA-2 laser facility (CLPU, Salamanca, Spain), the aim was to produce neutrons through photonuclear reactions on different types of solid targets. We have used the Timepix3 chip, in a “side-on” configuration, in order to produce a quick estimate of the gamma photons energy involved in the reactions. This detector, based on silicon, is realized with a single chip of 256 × 256 pixels bump-bonded with a 14 mm × 14 mm × 300 μm silicon layer. Interaction of gammas with the detector in this configuration produces some characteristic clusters of pixels and, for each cluster, a variety of physical and morphological parameters can be defined. Based on some of these parameters, we have characterized the detector response using some known laboratory gamma sources and the related Geant4 simulations. This allows quick energy discrimination for the gamma photons coming from different experimental runs.
This paper introduces a novel architecture for optimizing radiation shielding using a genetic algorithm with dynamic penalties and a custom parallel computing architecture. A practical example ...focuses on minimizing the Total Ionizing Dose for a silicon slab, considering only the layer number and the total thickness (additional constraints, e.g., cost and density, can be easily added). Genetic algorithm coupled with Geant4 simulations in a custom parallel computing architecture demonstrates convergence for the Total Ionizing Dose values. To address genetic algorithm issues (premature convergence, not perfectly fitted search parameters), a Total Ionizing Dose Database Vault object was introduced to enhance search speed (data persistence) and to preserve all solutions’ details independently. The Total Ionizing Dose Database Vault analysis highlights boron carbide as the best material for the first layer for neutron shielding and high-Z material (e.g., Tungsten) for the last layers to stop secondary gammas. A validation point between Geant4 and MCNP was conducted for specific simulation conditions. The advantages of the custom parallel computing architecture introduced here, are discussed in terms of resilience, scalability, autonomy, flexibility, and efficiency, with the benefit of saving computational time. The proposed genetic algorithm-based approach optimizes radiation shielding materials and configurations efficiently benefiting space exploration, medical devices, nuclear facilities, radioactive sources, and radiogenic devices.
The temperature dependence of the exciton dynamics in a conjugated polymer is studied using time-resolved spectroscopy. Photoluminescence decays were measured in heterostructured samples containing a ...sharp polymer−fullerene interface, which acts as an exciton quenching wall. Using a 1D diffusion model, the exciton diffusion length and diffusion coefficient were extracted in the temperature range of 4−293 K. The exciton dynamics reveal two temperature regimes: in the range of 4−150 K, the exciton diffusion length (coefficient) of ∼3 nm (∼1.5 × 10−4 cm2/s) is nearly temperature independent. Increasing the temperature up to 293 K leads to a gradual growth up to 4.5 nm (∼3.2 × 10−4 cm2/s). This demonstrates that exciton diffusion in conjugated polymers is governed by two processes: an initial downhill migration toward lower energy states in the inhomogenously broadened density of states, followed by temperature activated hopping. The latter process is switched off below 150 K.
The use of neural electrodes to stimulate the Peripheral Nervous System (PNS) of upper limb amputees is giving promising results in restoring tactile feedback. The same interfaces could be used to ...record the motor activity originated from the brain and transferred to the muscles. In this paper, the possibility to control a prosthetic hand by means of neural signals acquired through tf-LIFE4 electrodes implanted in a human subject was investigated. A Support Vector Machine (SVM) algorithm was adopted to classify two common demanded grasps. The obtained classes were converted into reference positions for a position-and-slippage control strategy that guarantees to perform stable grasps with a prosthetic hand avoiding slippage events. The achieved results showed an accuracy of the classifier higher than 90% and a success rate of the control strategy equal to 100%.
Thermal neutron detection plays a crucial role in numerous scientific and technical applications such as nuclear reactor physics, particle accelerators, radiotherapy, materials analysis and space ...exploration. There are several challenges associated with the accurate identification and quantification of thermal neutrons. The present work proposes a detailed characterization of a Timepix3 (TPX3) detector equipped with a Lithium Fluoride (
6
LiF) converter in order to study its response to thermal neutrons that are identified through the
6
Li(n,
α
)
3
H reaction. The TPX3-based test system has been installed at the HOTNES facility in ENEA and the analysis highlighted its excellent performance showing high effectiveness in the identification of neutrons through morphological analysis of tracks produced by alpha and triton particles, after accurate discrimination from the gamma background. With the use of Monte Carlo simulations, it has been demonstrated that the main contribution is due to tritons and its signal can be used effectively in the identification of thermal neutrons obtaining an efficiency of 0.9 % for 25 meV neutrons. This allows the TPX3 to have important applications as an environmental monitor for thermal neutrons. This monitoring system can be simply realized and is easy to manage because of its compact size and its digital acquisition that allows a real-time analysis.
This work presents an innovative usage of the GEMpix detector for soft X-rays (SXR) measurements aimed to make an estimate of the electron temperature of a Laser Produced Plasma (LPP). The GEMpix is ...a proportional gas detector based on three Gas Electron Multipliers (GEMs) with a Front-End Electronics (FEE) based on four Timepix chips. This FEE provides the Time over Threshold (ToT) acquisition mode pixel by pixel and then a digital measure of the released charge in the gas mixture. In addition, the charge can be amplified through the GEM foils with 4 orders of magnitude spanning gain offering, in this way, a big dynamic range and adjustable sensitivity. Chip design provides a threshold for each channel. All the thresholds are set in order to cut electronic noise and detect X-rays. In this configuration, a cut on the low amplitude signals is set, but the gain has been tuned in order to observe the main signal due to the soft X-rays reaching the detector. This detector works in an energy range between 2 to 15 keV . It offers good imaging properties, high efficiency and absolute calibration. It offers a good immunity to Electromagnetic Pulse (EMP), as checked at VEGA-2 laser facility (hundreds of TW in about 30 fs). In these experiments, where the formation of warm dense matter produced by blast waves has been studied, a measure of the plasma temperature was required. This measurement was realized applying some filters on the active area of the detector, in correspondence of three chips. With this configuration a study of the GEMpix response due to the photons coming from the coronal plasma produced by the laser on the target has been done for each single shot. GEMpix revealed innovative and attractive features, compared to the state of the art where passive films or detectors based on indirect conversion are used, for SXR imaging and spectral analysis to infer the electron temperature.
Diagnosing soft x-ray (SXR) emission from tokamaks represents a unique source of information, since it allows the study of several plasma parameters, such as the electron and ion temperature, the ...investigation of the ionization equilibrium, particle and impurities transport and the study of MHD fluctuations and disruptions. A new SXR diagnostic system called EXODUS (Enhanced X-ray Optimized Detector for Use in multiple Scenarios) is under development with the aim to obtain energy resolved SXR emission profiles from the plasma with a high time resolution (<0.1 ms). The system is based on the Gas Electron Multiplier (GEM) technology coupled with the new data acquisition system especially designed for GEM called GEMINI, which gives the possibility to obtain information about the energy deposited in the detector by the incoming radiation using the so called Time-Over-Threshold technique on each detector channel. The information of the deposited energy allows the study of the SXR emission from the plasma resolved in space, energy and time. There are several advantages in the use of GEM based detector in the harsh environment of a tokamak. First of all, it offers very high rate capabilities (up to 1 MHz/mm2), giving the possibility to obtain sub-ms time resolution together with sub-mm spatial resolution. The high counting rate and the high spatial resolution allow the installation of the detector in a pinhole camera very close to the tokamak vacuum barrier, producing very high statistic measurements. Finally, if properly designed, GEM detectors are intrinsically insensitive to gamma and neutron irradiation, allowing obtaining an excellent signal to noise ratio. In this contribution we describe the design and the production of the GEM based detector with the EXODUS system, together with the characterization of the detector response under quasi-monochromatic x-ray beam obtained using fluorescence of different materials. EXODUS electronics and its architecture allows the measurement of the energy of each detected photon and its time of arrival, resulting in a strong improvement of the energy and time resolution, compared to the old electronics used so far.
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