Artículos (Física Aplicada III)

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The Lyon Mint in the Roman Tomares Hoard (Seville): Some Considerations on Its Metallic Composition Determined by XRF
(Willey, 2025-06-15) Pliego Vázquez, Ruth; Gómez-Tubio, Blanca María; Alcaide Ramírez, María; Scrivano, Simona; Respaldiza Galisteo, Miguel Ángel; Física Atómica, Molecular y Nuclear; Prehistoria y Arqueología; Física Aplicada III; Ministerio de Ciencia, Innovación y Universidades (MICIU). España; Universidad de Sevilla
Multi-technique computational assessment of fluoride uptake in enamel using PIGE, NEXAFS, and Raman spectroscopy
(2025-05-12) Pessanha, Sofia; Fortes, António; Lopes, Marta B.; Guilherme Buzanich, Ana; Ortega-Feliú, Inés; Respaldiza Galisteo, Miguel Ángel; Gómez-Tubio, Blanca María; Silveira, João; Universidad de Sevilla. Departamento de Física Aplicada III; Universidad de Sevilla. Departamento de Física Atómica, Molecular y Nuclear; Fundação para a Ciência e a Tecnologia. Portugal
The uptake of fluoride in the enamel matrix is an effective strategy to prevent demineralization and caries formation. In this study a comprehensive methodology is developed to evaluate and understand the uptake of fluoride in human enamel. Twenty-six healthy anterior teeth were sectioned in half; one half remained untreated, while the other was treated with 50 mg mL−1 NaF (equivalent to 22.6 mg of fluoride) through three 1-minute applications over a 12-day period, following the manufacturer's guidelines. Fluoride uptake was quantified with particle-induced gamma-ray emission (PIGE), revealing an average increase of 160% in treated samples. The formation of calcium fluoride (CaF2) and fluorapatite-like structures was confirmed through near edge X-ray absorption fine structure (NEXAFS) analysis. Due to the absence of reference spectra for hydroxyapatite, fluorapatite, and calcium fluoride, finite difference method near edge structure (FDMNES) simulations were employed to computationally model the fluorine K-edge and the Ca L-edge spectra. Density functional theory (DFT) and time-dependent DFT (TDDFT) approaches were applied to enhance spectral accuracy, enabling a refined comparison with experimental data. To establish a rapid and laboratory-based screening technique, Raman microscopy was used to analyze fluoride-treated and untreated samples. Spectral data were evaluated using both full-spectrum analysis and specific spectral features, including band intensity, full-width at half maximum (FWHM) of Raman peaks, and phosphate symmetric stretching depolarization ratios. Furthermore, machine learning algorithms were applied to classify treated and untreated enamel samples. The random forest classifier demonstrated strong predictive performance, successfully distinguishing fluoride-treated samples. This methodological approach provides an effective framework for analyzing fluoride uptake in enamel, potentially guiding future preventive dentistry strategies.
Direct measurement of the electric field induced by a transcranial magnetic stimulator
(Institute of Electrical and Electronics Engineers, 2023-05-15) Freire Rosales, Manuel José; Bernal Méndez, Joaquín; Gutiérrez-Muto, Ane Miren; Oliviero, Antonio; Tornero, Jesús; Universidad de Sevilla. Departamento de Electrónica y Electromagnetismo; Universidad de Sevilla. Departamento de Física Aplicada III
This work proposes a simple method to carry out in the laboratory a direct measurement of the primary solenoidal electric field that transcranial magnetic stimulation (TMS) coils generate in the brain. This method avoids indirect estimation of this electric field from measurements of magnetic fields and, at the same time, overcomes the difficulty posed by the presence of a dominant conservative electric field, also produced by the coil. This conservative electric field, which is removed in practice by human tissue, is eliminated in the proposed measurement method by using a simple setup that does not require the introduction of the measurement probe inside a conducting solution resembling the human tissue. The proposed measurement method allows for measuring the primary solenoidal electric field in front of the coil in the air. This method has been validated by comparing the results of electromagnetic simulation with the measurement of the magnetic field and the nonconservative electric field produced by a commercial TMS coil.
Coulomb Driven Electro-Convection within Two Stacked Layers of Miscible Dielectric Liquids †
(Multidisciplinary Digital Publishing Institute (MDPI), 2024) Traore, P.; Pérez Izquierdo, Alberto Tomás; Mondal, S.; Bhattacharya, A.; Vázquez González, Pedro Ángel; Yan, Z.; Universidad de Sevilla. Departamento de Electrónica y Electromagnetismo; Universidad de Sevilla. Departamento de Física Aplicada III; Labex Interactifs. Francia; Ministerio de Ciencia e Innovación (MICIN). España
This article investigates the behavior of two parallel layers of different miscible dielectric liquids enclosed and sandwiched between two electrodes. By applying an electric potential to one electrode while grounding the other, electro-convection occurs when the electric Rayleigh number exceeds a critical value, setting the fluid into motion and resulting in rapid mixing between the two liquids. A numerical model is developed to account for the varying ionic mobility and permittivity of the two liquids, considering their evolution based on the relative concentration field. The simulations confirm that electro-convection significantly enhances the mixing between the two liquids, as expected. Additionally, intriguing ripples are observed near the initial interface during the early stages of electro-convection instability growth. To explain and describe the flow dynamics in terms of stability analysis, a semi-analytical model is presented. This study provides insights into the mixing behavior and flow dynamics of miscible dielectric liquids under the influence of electro-convection. The findings contribute to a better understanding of the underlying mechanisms and can be valuable for applications such as microfluidics, energy conversion, and mixing processes. Further research is encouraged to explore additional parameters and optimize the control of electro-convection for practical applications.
Compositional and microstructural study of joining methods in archaeological gold objects
(John Wiley and Sons Ltd, 2017-03) Scrivano, Simona; Gómez-Tubio, Blanca María; Ortega-Feliú, Inés; Ager Vázquez, Francisco José; Paúl Escolano, Antonio; Universidad de Sevilla. Departamento de Física Atómica, Molecular y Nuclear; Universidad de Sevilla. Departamento de Física Aplicada III; Universidad de Sevilla. Departamento de Física Aplicada I; Universidad de Sevilla. Departamento de Ingeniería y Ciencia de los Materiales y del Transporte; Ministerio de Economía y Competitividad (MINECO). España
This work arises in response to the need to understand the production techniques of pre-roman gold jewels, starting from the systematic characterization of the different methods of metal joining used in antiquity to produce these objects. To meet this requirement, different procedures used in antiquity were reproduced by means of experimental archaeology. These models correspond to three metal-joining methods reported by ancient recipes: solid-state diffusion with copper salt, brazing and autogenous welding. These techniques were studied by different analytical methods in order to characterize them at both compositional and microstructural level (SEM-EDS, metallography, μ-XRF and μ-PIXE). The results obtained show that the solid-state diffusion bonding with copper salt presents a crystal hexagonal structure without phase changes in the joining point, where only a variation in the grain size is observed. At the compositional level, this soldering method is characterized by a local increase in copper concentration and a small decrease in gold content. In contrast, brazing shows a dendritic-porous structure due to the superposition of the soldering alloy and the crystal structure of the original foils. Besides, the compositional analysis revealed an increment of silver and copper concentrations and a simultaneous reduction of gold concentration. Finally, in the autogenous welding, no changes at the microstructural and compositional levels were observed. The results obtained have also demonstrated the usefulness of a portable μ-XRF system for the in-situ characterization of ancient jewels.
Combining XRF and GRT for the analysis of ancient silver coins
(Elsevier, 2016-05) Ager Vázquez, Francisco José; Gómez-Tubio, Blanca María; Paúl Escolano, Antonio; Gómez-Morón, A.; Scrivano, Simona; Ortega-Feliú, Inés; Respaldiza Galisteo, Miguel Ángel; Universidad de Sevilla. Departamento de Física Atómica, Molecular y Nuclear; Universidad de Sevilla. Departamento de Física Aplicada I; Universidad de Sevilla. Departamento de Física Aplicada III; Universidad de Sevilla. Departamento de Ingeniería y Ciencia de los Materiales y del Transporte; Ministerio de Economía y Competitividad (MINECO). España
Archaeological silver-copper alloys are usually affected by silver enrichment of the near surface layers, either intentional or fortuitous. In previous studies we have shown that surface composition of archaeological bronzes and leaded copper coins obtained by XRF can be corrected by means of gamma-ray transmission (GRT) to obtain the bulk composition. In the present work, we have studied the applicability of this method to silver-copper alloys and established the most suitable conditions for the GRT correction calculation. The analysis of the microstructure of the core and the corrosion layers of a set of silver roman coins shows that copper could be leached from the surface during corrosion and cleaning treatments, resulting in an apparent silver surface enrichment. After the correction calculations by GRT method, the concentrations of the major elements, Ag and Cu, were found to be in good agreement with the bulk composition obtained by direct analysis of the cut cross-sections of the coins. The GRT method shows to be a useful tool to study metal artefacts having a surface composition modified by corrosion or cleaning treatments.
Wigner representation for entanglement swapping using parametric down conversion: the role of vacuum fluctuations in teleportation
(Taylor & Francis, 2015-03-12) Casado Rodríguez, Alberto; Guerra, Santiago; Plácido, José; Universidad de Sevilla. Departamento de Física Aplicada III
We apply the Wigner formalism of quantum optics in the Heisenberg picture to study the role of the zeropoint field fluctuations in entanglement swapping produced via parametric down conversion. It is shown that the generation of mode entanglement between two initially non-interacting photons is related to the quadruple correlation properties of the electromagnetic field, through the stochastic properties of the vacuum. The relationship between the process of transferring entanglement and the different zeropoint inputs at the non-linear crystal and the Bell-state analyser is emphasized.
Spectrum of the parametric down converted radiation calculated in the Wigner function formalism
(Springer, 2001-01) Casado Rodríguez, Alberto; Marshall, Trevor W.; Risco, Ramón; Santos, Emilio; Universidad de Sevilla. Departamento de Física Aplicada III
We continue the study of parametric down conversion within the framework of the Wigner representation, by using a Maxwellian approach developed in a recent paper [A. Casado et al., Eur. Phys. J. D 11, 465 (2000)]. This gives a mechanism, inside the crystal, for the production of the down-converted radiation. We obtain the electric field to second order in the coupling constant by using the Green's function method, and compare our treatment with the standard Hamiltonian approach. The spectrum of the down-converted radiation is calculated as a function of the parameters of the nonlinear crystal (in particular the length) and the radius of the pumping beam.
Wigner representation for experiments on quantum cryptography using two-photon polarization entanglement produced in parametric down-conversion
(IOP Publishing, 2008-02-28) Casado Rodríguez, Alberto; Guerra, Santiago; Plácido, José; Universidad de Sevilla. Departamento de Física Aplicada III
In this paper, the theory of parametric down-conversion in the Wigner representation is applied to Ekert's quantum cryptography protocol. We analyse the relation between two-photon entanglement and (non-secure) quantum key distribution within the Wigner framework in the Heisenberg picture. Experiments using two-qubit polarization entanglement generated in nonlinear crystals are analysed in this formalism, along with the effects of eavesdropping attacks in the case of projective measurements.
Rome teleportation experiment analysed in the Wigner representation: the role of the zeropoint fluctuations in complete one-photon polarization-momentum Bell-state analysis
(Taylor & Francis, 2018-10-07) Casado Rodríguez, Alberto; Guerra, Santiago; Plácido, José; Universidad de Sevilla. Departamento de Física Aplicada III
The Wigner representation of parametric down conversion in the Heisenberg picture is applied to the study of the Rome teleportation experiment. We investigate the physical meaning of the zeropoint inputs at the different areas of the experimental set-up. In particular, we establish a quantitative relationship between the zeropoint sets of modes that are needed for the preparation of the quantum state to be teleported, the idle channels inside the one-photon polarization-momentum Bell-state analyser, and the possibility of performing teleportation of a polarization state with certainty.
Wigner representation for polarization-momentum hyperentanglement generated in parametric down-conversion, and its application to complete Bell-state measurement
(Springer, 2014-11-06) Casado Rodríguez, Alberto; Guerra, Santiago; Plácido, José; Universidad de Sevilla. Departamento de Física Aplicada III
We apply the Wigner function formalism to the study of two-photon polarization-momentum hyperentanglement generated in parametric down-conversion. It is shown that the consideration of a higher number of degrees of freedom is directly related to the extraction of additional uncorrelated sets of zeropoint modes at the source. We present a general expression for the description of the quantum correlations corresponding to the sixteen Bell base states, in terms of four beams whose amplitudes are correlated through the stochastic properties of the zeropoint field. A detailed analysis of the two experiments on complete Bell-state measurement included in [Walborn et al., Phys. Rev. A 68, 042313 (2003)] is made, emphasizing the role of the zeropoint field. Finally, we investigate the relationship between the zeropoint inputs at the source and the analysers, and the limits on optimal Bell-state measurement.
Palladium analysis in gold items from Punic jewellery (Cádiz, Spain)
(Elsevier, 2020-02) Ortega-Feliú, Inés; Gómez Tubio, Ana María; Scrivano, Simona; Ager Vázquez, Francisco José; Bandera Romero, María Luisa de la; Respaldiza Galisteo, Miguel Ángel; Universidad de Sevilla. Departamento de Física Aplicada III; Universidad de Sevilla. Departamento de Física Aplicada I; Universidad de Sevilla. Departamento de Física Atómica, Molecular y Nuclear; Ministerio de Ciencia e Innovación (MICIN). España; Universidad de Sevilla; Universidad de Sevilla. RNM138: Física Nuclear Aplicada
Some years ago a group of jewels from the Museum of Cádiz (South Spain) was analysed by micro-PIXE (Particle Induced X-ray Emission) at Centro Nacional de Aceleradores (Sevilla). During this work two similar spiral earrings happened to have significant amounts of palladium in their composition, up to 0.7 wt%, and some hypotheses about the provenance of this palladium-bearing gold were exposed. Many similar gold earrings from the same location and time are kept in the museum, some of them permanently exhibited in the showcases. Now, by means of a portable X-ray spectrometer device, especially designed for the analysis of gold jewels, a second campaign has been accomplished to study the rest of the jewels kept at the museum. This time the equipment was moved to the museum instead of taking the gold items to the laboratory, facilitating the analysis of the samples in the showcases and reducing the costs. A total of 94 jewels have been studied and 24 of them contained palladium up to 1.1 wt%. Copper content was below 2.5 wt% in most of the cases. X Ray Fluorescence technique was employed for this study. A filter of 20 μm of Zn was used in the detector to enhance the detection of palladium, and other potential platinum group elements, by absorbing the Au-Lα emission line. The effects of this method in the quantification was also compared in this work, finding higher uncertainties with the use of the filter, but demonstrating the convenience of its use to discriminate the Pd-Kα line from the sum peaks of the very intense gold lines.
Fluoride exposure duringintrauterine and lactation periods promotes changes in the offspring rats' alveolar bone
(Elsevier, 2022-11) Ferreira, Maria Karolina Martins; Souza-Monteiro, Deiweson; Bittencourt, Leonardo Oliveira; Matos-Sousa, José Mário; Chemelo, Victória Santos; Santos, Vinicius Ruan Neves; Nunes, Paula Beatriz Oliveira; Balbinot, Gabriela de Souza; Prado, Alejandro Ferraz; Collares, Fabricio Mezzomo; Ager Vázquez, Francisco José; Ortega-Feliú, Inés; Respaldiza Galisteo, Miguel Ángel; Pessanha, Sofia; Lima, Rafael Rodrigues; Universidad de Sevilla. Departamento de Física Aplicada I; Universidad de Sevilla. Departamento de Física Aplicada III; Universidad de Sevilla. Departamento de Física Atómica, Molecular y Nuclear; Universidad de Sevilla. RNM138: Física Nuclear Aplicada
The importance of fluoride (F) for oral health is well established in the literature. However, evidence suggests that excessive exposure to this mineral is associated with adverse effects at different life stages and may affect many biological systems, especially mineralized tissues. The purpose of this study was to investigate the effects of F exposure during pregnancy and breastfeeding on the alveolar bone of the offspring since the alveolar bone is one of the supporting components of the dental elements. For this, the progeny rats were divided into three groups: control, 10 mg F/L, and 50 mg F/L for 42 (gestational and lactation periods). Analysis of the quantification of F levels in the alveolar bone by particle-induced gamma emission; Raman spectroscopy to investigate the physicochemical aspects and mineral components; computed microtomography to evaluate the alveolar bone microstructure and analyses were performed to evaluate osteocyte density and collagen quantification using polarized light microscopy. The results showed an increase in F levels in the alveolar bone, promoted changes in the chemical components in the bone of the 50 mg F/L animals (p < 0.001), and had repercussions on the microstructure of the alveolar bone, evidenced in the 10 mg F/L and 50 mg F/L groups (p < 0.001). Furthermore, F was able to modulate the content of organic bone matrix, mainly collagen; thus, this damage possibly reduced the amount of bone tissue and consequently increased the root exposure area of the exposed groups in comparison to a control group (p < 0.001). Our findings reveal that Fcan modulate the physicochemical and microstructural dimensions and reduction of alveolar bone height, increasing the exposed root region of the offspring during the prenatal and postnatal period. These findings suggest that F can modulate alveolar bone mechanical strength and force dissipation functionality.
Análisis metalográficos de monedas procedentes de cecas púnicas del norte de África y del sur de la Península Ibérica
(Société Royale de Numismatique de Belgique, 1999) Chaves Tristán, Francisca Asís; Pliego Vázquez, Ruth; Gómez-Tubio, Blanca María; Respaldiza Galisteo, Miguel Ángel; Universidad de Sevilla. Departamento de Prehistoria y Arqueología; Universidad de Sevilla. Departamento de Física Aplicada III; Universidad de Sevilla. Departamento de Física Atómica, Molecular y Nuclear; Universidad de Sevilla. HUM152: De la Turdetania a la Bética; Universidad de Sevilla. RNM138: Física nuclear aplicada
Developing the IBA equipment to increase the versatility of the CNA
(Elsevier, 2012-02-15) Morilla García, Yolanda; Jiménez Ramos, María del Carmen; García López, Francisco Javier; Labrador Bernal, Juan Ángel; Palomo Pinto, Rogelio; Ortega-Feliú, Inés; Universidad de Sevilla. Departamento de Física Aplicada II; Universidad de Sevilla. Departamento de Física Atómica, Molecular y Nuclear; Universidad de Sevilla. Departamento de Ingeniería Electrónica; Universidad de Sevilla. Departamento de Física Aplicada III; Ministerio de Ciencia, Innovación y Universidades (MICINN). España; Universidad de Sevilla. RNM138: Física Nuclear Aplicada; Universidad de Sevilla. TIC192: Ingeniería Electrónica
The Centro Nacional de Aceleradores (CNA) in Sevilla-Spain currently contains three accelerators: two Tandems and a compact 18/9 Cyclotron. Next year, a 60Co irradiation system will also be installed. This equipment will expand the range of irradiation experiments in the Centre using both charged particles as well as gamma-ray photons. Originally, based on the 3 MV tandem accelerator, the CNA was considered as a multidisciplinary research Centre devoted basically to the materials characterization by IBA techniques. Nowadays, the validity of our low-energy accelerators has been verified not only to perform analysis but also for irradiation testing, a very promising field of work since radiation effects are aggravated with the technology decreasing scales. In this work, the last innovations and modifications of our laboratory will be briefly described, emphasizing with respect to high energy PIXE experiments and its versatility to carry out irradiation tests.
Relaxation time as a control parameter for exploring dynamical phase diagrams
(2023-11) Corps, Ángel L.; Pérez Fernández, Pedro; Relaño, Armando; Universidad de Sevilla. Departamento de Física Aplicada III; Ministerio de Ciencia e Innovación (MICIN). España; Agencia Estatal de Investigación. España; European Commission (EC). Fondo Europeo de Desarrollo Regional (FEDER); Consejería de Conocimiento, Investigación y Universidad, Junta de Andalucía; Universidad de Sevilla. FQM160: Física Nuclear Básica
We explore a full dynamical phase diagram by means of a double quench protocol that depends on a relaxation time as the only control parameter. The protocol comprises two fixed quenches and an intermediate relaxation time that determines the phase in which the quantum state is placed after the final quench. We apply it to an anharmonic Lipkin-Meshkov-Glick model. We show that its two excited-state quantum phase transitions split the spectrum into three different phases: two symmetry-breaking ones, characterized by different constants of motion, and a disordered phase. As a consequence, our protocol allows us to explore all the dynamical phase transitions arising from two kinds of quenches: the typical one, leading the system from a symmetry-breaking to a disordered phase, and another one in which the system transitions between two different symmetry-breaking phases. We characterize all of them in terms of the constants of motion appearing in all three phases of the model.
The use of high-intensity focused ultrasound for the rewarming of cryopreserved biological material
(IEEE, 2021) Olmo Fernández, Alberto; Barroso, Pablo; Barroso, Fátima; Risco, Ramón; Universidad de Sevilla. Departamento de Tecnología Electrónica; Universidad de Sevilla. Departamento de Física Aplicada III
High-intensity focused ultrasound (HIFU) has been used in differentmedical applications in the last years. In this work, we present for the first time the use of HIFU in the field of cryopreservation, the preservation of biological material at low temperatures. An HIFU system has been designed with the objective of achieving a fast and uniform rewarming in organs, key to overcome the critical problem of devitrification. The finite-element simulations have been carried out using COMSOL Multiphysics software. An array of 26 ultrasonic transducers was simulated, achieving an HIFU focal area in the order of magnitude of a model organ (ovary). A parametric study of the warming rate and temperature gradients, as a function of the frequency and power of ultrasonicwaves,was performed.An optimal value for these parameters was found. The results validate the appropriateness of the technique,which is of utmost importance for the future creation of cryopreserved organ banks.
Overview of the EUROfusion Tokamak Exploitation programme in support of ITER and DEMO
(Institute of Physics Publishing, 2024-11-01) Jet Contributors; Ayllón Guerola, Juan Manuel; Cruz Zabala, Diego José; Domínguez-Palacios Durán, Jesús José; Doyle, Scott James; Galdón Quiroga, Joaquín; García Muñoz, Manuel; Hidalgo Salaverri, Javier; Mancini, Alessio; McKay, Kiera Anne; Oyola Domínguez, Pablo; Rivero Rodríguez, Juan Francisco; Romero Madrid, Carlos Francisco; Rueda Rueda, José; Toscano Jiménez, Manuel; Van Vuuren, Anton Jansen; Velarde Gallardo, Lina; Viezzer, Eleonora; Universidad de Sevilla. Departamento de Física Atómica, Molecular y Nuclear; Universidad de Sevilla. Departamento de Física Aplicada III; Universidad de Sevilla. Departamento de Ingeniería Energética; Universidad de Sevilla. Departamento de Ingeniería Mecánica y de Fabricación; EUROfusion Consortium
Within the 9th European Framework programme, since 2021 EUROfusion is operating five tokamaks under the auspices of a single Task Force called ‘Tokamak Exploitation’. The goal is to benefit from the complementary capabilities of each machine in a coordinated way and help in developing a scientific output scalable to future largre machines. The programme of this Task Force ensures that ASDEX Upgrade, MAST-U, TCV, WEST and JET (since 2022) work together to achieve the objectives of Missions 1 and 2 of the EUROfusion Roadmap: i) demonstrate plasma scenarios that increase the success margin of ITER and satisfy the requirements of DEMO and, ii) demonstrate an integrated approach that can handle the large power leaving ITER and DEMO plasmas. The Tokamak Exploitation task force has therefore organized experiments on these two missions with the goal to strengthen the physics and operational basis for the ITER baseline scenario and for exploiting the recent plasma exhaust enhancements in all four devices (PEX: Plasma EXhaust) for exploring the solution for handling heat and particle exhaust in ITER and develop the conceptual solutions for DEMO. The ITER Baseline scenario has been developed in a similar way in ASDEX Upgrade, TCV and JET. Key risks for ITER such as disruptions and run-aways have been also investigated in TCV, ASDEX Upgrade and JET. Experiments have explored successfully different divertor configurations (standard, super-X, snowflakes) in MAST-U and TCV and studied tungsten melting in WEST and ASDEX Upgrade. The input from the smaller devices to JET has also been proven successful to set-up novel control schemes on disruption avoidance and detachment.
An arbitrary waveform neurostimulator for preclinical studies: design and verification
(Springer, 2024-12-12) Guzmán-Miranda, Hipólito; Barriga-Rivera, Alejandro; Universidad de Sevilla. Departamento de Física Aplicada III; Universidad de Sevilla. Departamento de Ingeniería Electrónica; Ministerio de Ciencia, Innovación y Universidades (MICINN). España; Agencia Estatal de Investigación. España; European Union (UE)
Neural electrostimulation has enabled different therapies to treat a number of health problems. For example, the cochlear implant allows for recovering the hearing function and deep brain electrostimulation has been proved to reduce tremor in Parkinson’s disease. Other approaches such as retinal prostheses are progressing rapidly, as researchers continue to investigate new strategies to activate targeted neurons more precisely. The use of arbitrary current waveform electrosimulation is a promising technique that allows exploiting the differences that exist among different neural types to enable preferential activation. This work presents a two-channel arbitrary waveform neurostimulator designed for visual prosthetics research. A field programmable gate array (FPGA) was employed to control and generate voltage waveforms via digital-to-analog converters. Voltage waveforms were then electrically isolated and converted to current waveforms using a modified Howland amplifier. Shorting of the electrodes was provided using multiplexers. The FPGA gateware was verified to a high level of confidence using a transaction-level modeled testbench, achieving a line coverage of 91.4%. The complete system was tested in saline using silver electrodes with diameters from 200 to 1000 µm. The bandwidth obtained was 30 kHz with voltage compliance ± 15 V. The neurostimulator can be easily scaled up using the provided in/out trigger ports and adapted to other applications with minor modifications.
Structural brain preservation: a potential bridge to future medical technologies
(Frontiers Media, 2024-10) McKenzie, Andrew T.; Zeleznikow-Johnston, Ariel; Sparks, Jordan S.; Nnadi, Oge; Smart, John; Wiley, Keith; Risco, Ramón; Universidad de Sevilla. Departamento de Física Aplicada III; Universidad de Sevilla. BIO289: Cryobiotech: Criopreservación de Tejidos y Órganos
When faced with the prospect of death, some people would prefer a form of long-term preservation that may allow them to be restored to healthy life in the future, if technology ever develops to the point that this is feasible and humane. Some believe that we may have the capacity to perform this type of experimental preservation today—although it has never been proven—using contemporary methods to preserve the structure of the brain. The idea is that the morphomolecular organization of the brain encodes the information required for psychological properties such as personality and long-term memories. If these structures in the brain can be maintained intact over time, this could theoretically provide a bridge to access restorative technologies in the future. To consider this hypothesis, we first describe possible metrics that can be used to assess structural brain preservation quality. We next explore several possible methods to preserve structural information in the brain, including the traditional cryonics method of cryopreservation, as well as aldehyde-stabilized cryopreservation and fluid preservation. We focus in-depth on fluid preservation, which relies on aldehyde fixation to induce chemical gel formation in a wide set of biomolecules and appears to be a cost-effective method. We describe two theoretical recovery technologies, alongside several of the ethical and legal complexities of brain preservation, all of which will require a prudent approach. We believe contemporary structural brain preservation methods have a non-negligible chance of allowing successful restoration in the future and that this deserves serious research efforts by the scientific community.

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