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On the statistical relationship between CME speed and soft X-ray flux and fluence of the associated flare
(2015-04-10) Salas Matamoros, Carolina; Klein, Karl Ludwig
Both observation and theory reveal a close relationship between the kinematics of coronal mass ejections (CMEs) and the thermal energy release traced by the related soft X-ray (SXR) emission. The major problem of empirical studies of this relationship is the distortion of the CME speed by the projection effect in the coronagraphic measurements. We present a re-assessment of the statistical relationship between CME velocities and SXR parameters, using the SOHO/LASCO catalog and GOES whole Sun observations during the period 1996 to 2008. 49 events were identified where CMEs originated near the limb, at central meridian distances between 70◦ and 85◦, and had a reliably identified SXR burst, the parameters of which - peak flux and fluence - could be determined with some confidence. We find similar correlations between the logarithms of CME speed and of SXR peak flux and fluence as several earlier studies, with correlation coefficients of 0.48 and 0.58, respectively. Correlations are slightly improved over an unrestricted CME sample when only limb events are used. However, a broad scatter persists. We derive the parameters of the CME-SXR relationship and use them to predict ICME arrival times at Earth. We show that the CME speed inferred from SXR fluence measurements tends to perform better than SoHO/LASCO measurements in the prediction of ICME arrival times near 1 AU. The estimation of the CME speed from SXR observations can therefore make a valuable contribution to space weather predictions.
Coronal mass ejection-related particle acceleration regions during a simple eruptive event
(2016-05-31) Salas Matamoros, Carolina; Klein, Karl Ludwig; Rouillard, Alexis P.
An intriguing feature of many solar energetic particle (SEP) events is the detection of particles over a very extended range of longitudes in the heliosphere. This may be due to peculiarities of the magnetic field in the corona, to a broad accelerator, to cross-field transport of the particles, or to a combination of these processes. The eruptive flare on 26 April 2008 provided an opportunity to study relevant processes under particularly favourable conditions since it occurred in a very quiet solar and interplanetary environment. This enabled us to investigate the physical link between a single well-identified coronal mass ejection (CME), electron acceleration as traced by radio emission, and the production of SEPs. We conduct a detailed analysis, which combines radio observations (Nançay Radio Heliograph and Nançay Decametre Array, Wind/Waves spectrograph) with remote-sensing observations of the corona in extreme ultraviolet (EUV) and white light, as well as in situ measurements of energetic particles near 1AU (SoHO and STEREO spacecraft). By combining images taken from multiple vantage points, we were able to derive the time-dependent evolution of the 3D pressure front that was developing around the erupting CME. Magnetic reconnection in the post-CME current sheet accelerated electrons, which remained confined in closed magnetic fields in the corona, while the acceleration of escaping particles can be attributed to the pressure front ahead of the expanding CME. The CME accelerated electrons remotely from the parent active region, owing to the interaction of its laterally expanding flank, which was traced by an EUV wave, with the ambient corona. SEPs detected at one STEREO spacecraft and SoHO were accelerated later, when the frontal shock of the CME intercepted the spacecraft-connected interplanetary magnetic field line. The injection regions into the heliosphere inferred from the radio and SEP observations are separated in longitude by about 140◦. The observations for this event show that it is misleading to interpret multi-spacecraft SEP measurements in terms of one acceleration region in the corona. The different acceleration regions are linked to different vantage points in the interplanetary space.
Microwave radio emissions as a proxy for coronal mass ejection speed in arrival predictions of interplanetary coronal mass ejections at 1 AU
(2017-01-12) Salas Matamoros, Carolina; Klein, Karl Ludwig; Trottet, Gerard
The propagation of a coronal mass ejection (CME) to the Earth takes between about 15 h and several days. We explore whether observations of non-thermal microwave bursts, produced by near-relativistic electons via the gyrosynchrotron process, can be used to predict travel times of interplanetary coronal mass ejections (ICMEs) from the Sun to the Earth. In a first step, a rela- tionship is established between the CME speed measured by the Solar and Heliospheric Observatory/Large Angle and Spectro- metric Coronagraph (SoHO/LASCO) near the solar limb and the fluence of the microwave burst. This relationship is then employed to estimate speeds in the corona of earthward-propagating CMEs. These speeds are fed into a simple empirical inter- planetary acceleration model to predict the speed and arrival time of the ICMEs at Earth. The predictions are compared with observed arrival times and with the predictions based on other proxies, including soft X-rays (SXR) and coronographic measure- ments. We found that CME speeds estimated from microwaves and SXR predict the ICME arrival at the Earth with absolute errors of 11 ± 7 and 9 ± 7 h, respectively. A trend to underestimate the interplanetary travel times of ICMEs was noted for both techniques. This is consistent with the fact that in most cases of our test sample, ICMEs are detected on their flanks. Although this preliminary validation was carried out on a rather small sample of events (11), we conclude that microwave proxies can provide early estimates of ICME arrivals and ICME speeds in the interplanetary space. This method is limited by the fact that not all CMEs are accompanied by non-thermal microwave bursts. But its usefulness is enhanced by the relatively simple observational setup and the observation from ground, which makes the instrumentation less vulnerable to space weather hazards
Statistical relationship between CME speed and soft X-ray peak flux of the associated flare during solar cycle 23
(2014-01-06) Salas Matamoros, Carolina; Klein, Karl Ludwig; Taliashvili Enacolopas, Lela
The relationship between the speed of coronal mass ejections and the peak soft X-ray flux of the associated flares is studied for events occurring near the solar limbs between 1996 and 2008. An improved, though still moderate, correlation between the two parameters is found.
On the relationship between expansion angle of Earth-directed CMES and soft X-ray emission from their related flare
(2023-07-14) Salas Matamoros, Carolina; Sánchez Guevara, Jesús
In space weather, to study the impact of Earth-directed coronal mass ejections (CME) in our terrestrial environment, one of the most important parameters is the propagation speed of these disturbances. We present an improvement of the 3D CME Geometrical Propagation-Expansion Description (3D-CGPED) model developed in previous work to increase the sample that we can use in CME arrival time predictions. This 3D model estimates the arrival time of Earth-directed CMEs at Earth by including a 3D geometry for the CME propagation and expansion in interplanetary space. Since the 3D-CGPED model computes the expansion of the CME based on the radial distance of the CME front, only travel times for CMEs with well-defined shapes seen by coronographs can be estimated. In the present work, we found an empirical relationship between the expansion angle of CMEs with well-defined shapes and the start-to-peak SXR fluence of their associated flares. We applied this relationship in the 3D-CGPED model to obtain the expansion angle for 8 CMEs with an irregular shape. We found similar window errors in arrival time predictions compared to the previous work. This result allows us to complement the 3D-CGPED model to include not only regular shapes but also irregular ones for CMEs observed by coronographs in future works.
Comprehensive characterization of solar eruptions with remote and in-situ observations, and modeling: the major solar events on 4 November 2015
(2020-02-20) Cairns, Iver H.; Kozarev, Kamen A.; Nitta, Nariaki V.; Àgueda Costafreda, Neus; Battarbee, Markus; Carley, Eoin P.; Dresing, Nina; Gómez Herrero, Raúl; Klein, Karl Ludwig; Lario, David; Pomoell, Jens; Salas Matamoros, Carolina; Veronig, Astrid M.; Li, Bo; McCauley, Patrick
Solar energetic particles (SEPs) are an important product of solar activity. They are connected to solar active regions and flares, coronal mass ejections (CMEs), EUV waves, shocks, Type II and III radio emissions, and X- ray bursts. These phenomena are major probes of the partition of energy in solar eruptions, as well as for the organization, dynamics, and relaxation of coronal and interplanetary magnetic fields. Many of these phenomena cause terrestrial space weather, posing multiple hazards for humans and their technology from space to the ground. Since particular flares, shocks, CMEs, and EUV waves produce SEP events but others do not, since propagation effects from the low corona to 1 AU appear important for some events but not others, and since Type II and III radio emissions and X-ray bursts are sometimes produced by energetic particles leaving these acceleration sites, it is necessary to study the whole system with a multi-frequency and multi-instrument perspective that combines both in-situ and remote observations with detailed modelling of phenomena. This article demonstrates this comprehensive approach, and shows its necessity, by analysing a trio of unusual and striking solar eruptions, radio and X-ray bursts, and SEP events that occurred on 4 November 2015. These events show both strong similarities and differences from standard events and each other, despite having very similar interplanetary conditions and only two flare sites and CME genesis regions. They are therefore major targets for further in-depth observational studies, and for testing both existing and new theories and models. We present the complete suite of relevant observations, complement them with initial modelling results for the SEPs and interplanetary magnetic connectivity, and develop a plausible scenario for the eruptions. Perhaps controversially, the SEPs appear to be reasonably modelled and evidence points to significant non- Parker magnetic fields. Based on the very limited modelling available we identify the aspects that are and are not understood, and we discuss ideas that may lead to improved understanding of the SEP, radio, and space-weather events.
A geometrical description for interplanetary propagation of Earth-directed CMEs based on radiative proxies
(2021-05-03) Salas Matamoros, Carolina; Sánchez Guevara, Jesús
We present a 3D geometrical model to describe the propagation and expansion of coronal mass ejections (CMEs) in the interplanetary space based on radiative proxies to be implemented in previous procedures that use SXR and microwave emissions to estimate the Earth-directed CME propagation speed. We carefully selected a sample of 45 well-defined CME-ICME events to evaluate our model. We computed this 3D geometrical model for each event as a tool to improve the arrival time predictions based on radiative proxies. We conducted a different analysis for each radiative proxy: SXR emission and microwave emission at 9 GHz, and we compared the results separately with the observations by the Wind spacecraft. In general, the results showed that the implementation of our 3D geometrical model improves the predictions and provides an important complement to the arrival time prediction method based on radiative proxies, especially for CME events whose source origin were located at helio longitudes far from the central meridian at least 10◦. Improvements for this tool based on observations by Parker Solar Probe and Solar Orbiter must be developed in the future work.
Polarisation and source structure of solar stationary type IV radio bursts
(2020-07-16) Salas Matamoros, Carolina; Klein, Karl Ludwig
The reconfiguration of the magnetic field during and after a coronal mass ejection (CME) may be accompanied by radio emission from non-thermal electrons. In particular, stationary type IV bursts (also called storm continua) are emitted by electrons in closed magnetic configurations usually located in the wake of the outward-travelling CME. Although stationary type IV bursts, which stand out by their long duration (up to several hours) and strong circular polarisation, have been known for more than fifty years, there have been no systematic studies since the 1980s. In this work we use the data pool of the Nançay Radioheliograph together with white-light coronagraphy, EUV imaging and magnetography from the SoHO, Proba2, SDO and STEREO spacecraft to revisit the source structure and polarisation of a sample of seven well-defined stationary type IV bursts at decimetre-to-metre wavelengths. The radio sources are most often found in one leg, in one case both legs, of the magnetic flux rope erupting into the high corona during the CME. The cross-correlation of the brightness temperature time profiles in the event with sources in both legs implies that the radiating electrons have energies of a few tens of keV. Comparison with the magnetic field measured in the photosphere and its potential extrapolation into the corona shows that the radio emission is in the ordinary mode. This result was inferred historically by means of the hypothesis that the magnetic field orientation in the radio source was that of the dominant sunspot in the parent active region. This hypothesis is shown here to be in conflict with noise storms in the same active region. It is confirmed that the polarisation of stationary type IV continua may be strong, but is rarely total, and that it gradually increases in the early phase of the radio event. We find that the increase is related to the gradual disappearance of some weakly polarised or unpolarised substructure, which dominates the first minutes of the radio emission.
Non-thermal electrons in an eruptive solar event: Magnetic structure, confinement, and escape into the heliosphere
(2024-07-30) Klein, Karl Ludwig; Salas Matamoros, Carolina; Hamini, Abdallah; Kollhoff, Alexander
Context. Filament eruptions and coronal mass ejections (CMEs) reveal large-scale instabilities of magnetic structures in the solar corona. Some of them are accompanied by radio emission, which at decimetric and longer wavelengths is a signature of electron acceleration that may be different from the acceleration in impulsive flares. The radio emission is part of the broadband continua at decimetre and metre wavelengths called type IV bursts. Aims. In this article we investigate a particularly well-observed combination of a filament eruption seen in Hα and at extreme ultraviolet (EUV) wavelengths and a moving type IV burst on 2021 August 24. The aim is to shed light on the relationship between the large-scale erupting magnetic structure and the acceleration and transport of non-thermal electrons. Methods. We used imaging observations of a moving radio source and associated burst groups with the refurbished Nançay Radioheliograph and whole-Sun radio spectrography from different ground-based and space-borne instruments, in combination with X-ray, radio, and in situ electron observations at tens of keV from Solar Orbiter and EUV imaging by SDO/AIA. The radio sources are located with respect to the erupting magnetic structure traced by the filament (EUV 30.4 nm), and the timing of the electrons detected in situ is compared with the timing of the different radio emissions. Results. We find that the moving radio source is located at the top of the erupting magnetic structure outlined by the filament, which we interpret as a magnetic flux rope. The flux rope erupts in a strongly non-radial direction, guided by the overlying magnetic field of a coronal hole. The electrons detected at Solar Orbiter are found to be released mainly in two episodes, 10–40 minutes after the impulsive phase. The releases coincide with two groups of radio bursts, which originate respectively on the flank and near the top of the erupting flux rope. Conclusions. The observation allows an unusually clear association between a moving type IV radio burst, an erupting magnetic flux rope as core structure of a CME, and particle releases into the heliosphere. Non-thermal electrons are confined in the flux rope. Electrons escape to the heliosphere mainly in two distinct episodes, which we relate to magnetic reconnection between the flux rope and ambient open field lines.
Quantum thermodynamics of de Sitter space
(2023-12-18) Alicki, Robert; Barenboim Szuchman, Gabriela Alejandra; Jenkins Villalobos, Alejandro
We consider the local physics of an open quantum system embedded in an expanding three-dimensional space x, evolving in cosmological time t, weakly coupled to a massless quantum field. We derive the corresponding Markovian master equation for the system's nonunitary evolution and show that, for a de Sitter space with Hubble parameter h = const., the background fields act as a physical heat bath with temperature T_dS = h/2π. The energy density of this bath obeys the Stefan-Boltzmann law ρ_dS \propto h^4. We comment on how these results clarify the thermodynamics of de Sitter space and support previous arguments for its instability in the infrared. The cosmological implications are considered in an accompanying letter.
Exact cosmological solutions and their stability for a non-linear scalar field equivalent to a mixture of dark energy, dust, and stiff matter in a symmetry of petrov type D
(2024) Angulo Sibaja, Andrés Alexis; Alvarado Marín, Rodrigo
En este trabajo se encuentran soluciones cosmológicas exactas en una simetría de Petrov tipo D para un campo escalar equivalente a una mezcla de tres fluidos perfectos: energía oscura, polvo y materia rígida. Se estudia la evolución dinámica del universo y determinan los parámetros cosmológicos y singularidades con el escalar de Kretschmann. Finalmente, con la teoría de Kosambi-Cartan-Chern, se calcula la estabilidad de Jacobi de la cosmología con el campo escalar para analizar la robustez del modelo ante desviaciones exponenciales de trayectorias cercanas.
Microfluidic systems and devices for molecular capture, manipulation, and analysis
(2018-03-13) Chou, Chia-Fu; Lesser Rojas, Leonardo; Chu, Ming-Lee; Erbe, Andreas
Methods, systems, and devices are disclosed for molecular capture, manipulation, and analysis. In one aspect, a device to aggregate and characterize particles in a fluid includes an electrically insulative substrate including a channel to carry an electrically conducting fluid containing particles, electrodes located in the channel forming a nanoscale opening and including an insulating layer over their surface at the opening, a first circuit to apply a non-uniform ac electric field and a dc bias signal across the electrodes, in which the applied non-uniform ac electric field produces a positive dielectrophoretic force to aggregate the particles in a trapping region including the opening and adjacent region, a second circuit to detect changes in a dc current caused by at least some of the particles in the trapping region, and an optical device that directs a coherent light beam on the opening to determine Raman spectra of the particles in the trapping region.
Microfluidic blood separation: key technologies and critical figures of merit
(2023-11-18) Torres Castro, Karina; Acuña Umaña, Katherine; Lesser Rojas, Leonardo; Reyes, Darwin R.
Blood is a complex sample comprised mostly of plasma, red blood cells (RBCs), and other cells whose concentrations correlate to physiological or pathological health conditions. There are also many blood-circulating biomarkers, such as circulating tumor cells (CTCs) and various pathogens, that can be used as measurands to diagnose certain diseases. Microfluidic devices are attractive analytical tools for separating blood components in point-of-care (POC) applications. These platforms have the potential advantage of, among other features, being compact and portable. These features can eventually be exploited in clinics and rapid tests performed in households and low-income scenarios. Microfluidic systems have the added benefit of only needing small volumes of blood drawn from patients (from nanoliters to milliliters) while integrating (within the devices) the steps required before detecting analytes. Hence, these systems will reduce the associated costs of purifying blood components of interest (e.g., specific groups of cells or blood biomarkers) for studying and quantifying collected blood fractions. The microfluidic blood separation field has grown since the 2000s, and important advances have been reported in the last few years. Nonetheless, real POC microfluidic blood separation platforms are still elusive. A widespread consensus on what key figures of merit should be reported to assess the quality and yield of these platforms has not been achieved. Knowing what parameters should be reported for microfluidic blood separations will help achieve that consensus and establish a clear road map to promote further commercialization of these devices and attain real POC applications. This review provides an overview of the separation techniques currently used to separate blood components for higher throughput separations (number of cells or particles per minute). We present a summary of the critical parameters that should be considered when designing such devices and the figures of merit that should be explicitly reported when presenting a device’s separation capabilities. Ultimately, reporting the relevant figures of merit will benefit this growing community and help pave the road toward commercialization of these microfluidic systems.
Applications of single-molecule vibrational spectroscopic techniques for the structural investigation of amyloid oligomers
(2022-09-30) Vu, Katrin Ha Phuong; Blankenburg, Gerhard Heinrich; Lesser Rojas, Leonardo; Chou, Chia-Fu
Amyloid oligomeric species, formed during misfolding processes, are believed to play a major role in neurodegenerative and metabolic diseases. Deepening the knowledge about the structure of amyloid intermediates and their aggregation pathways is essential in understanding the underlying mechanisms of misfolding and cytotoxicity. However, structural investigations are challenging due to the low abundance and heterogeneity of those metastable intermediate species. Single-molecule techniques have the potential to overcome these difficulties. This review aims to report some of the recent advances and applications of vibrational spectroscopic techniques for the structural analysis of amyloid oligomers, with special focus on single-molecule studies.
Time-evolved SERS signatures of DEP-trapped Aβ and Zn2+Aβ peptides revealed by a sub-10 nm electrode nanogap
(2021-11-24) Vu, Katrin Ha Phuong; Lee, Ming-Che; Blankenburg, Gerhard Heinrich; Chang, Yu-Jen; Villalobos Rojas, Luis Vidal; Erbe, Andreas; Lesser Rojas, Leonardo; Chen, Yun-Ru; Chou, Chia-Fu
Alzheimer’s disease (AD) has become highly relevant in aging societies, yet the fundamental molecular basis for AD is still poorly understood. New tools to study the undergoing structural conformation changes of amyloid beta (Aβ) peptides, the pathogenic hallmark of AD, could play a crucial role in the understanding of the underlying mechanisms of misfolding and cytotoxicity of this peptide. It has been recently reported that Zn2+ interacts with Aβ and changes its aggregation pathway away from less harmful fibrillar forms to more toxic species. Here, we present a versatile platform based on a set of sub-10 nm nanogap electrodes for the manipulation and sensing of biomolecules in the physiological condition at a low copy number, where molecules are trapped via dielectrophoresis (DEP) across the nanogap, which also serves as a surface-enhanced Raman spectroscopy hotspot. In this study, we demonstrate that our electrode nanogap platform can be used to study the structural difference between Aβ40 and ZnAβ40 peptides at different aggregation stages in the physiologically relevant concentration and in solution phase. The Raman spectroscopic signatures of the DEP-captured neuropeptides prove the device to be attractive as a label-free bioanalytical tool.
Combined electrokinetic manipulations of pathogenic bacterial samples in low-cost fabricated dielectrophoretic devices
(2019-11-13) Martínez Brenes, Alejandro; Torres Castro, Karina; Espinoza Araya, Christopher; Acuña Umaña, Katherine; Ramírez Carranza, Raquel; González Espinoza, Gabriela; Rojas Castro, Norman; Guzmán Verri, Caterina; Sáenz Arce, Giovanni; Lesser Rojas, Leonardo; Marín Benavides, Richard
A low-cost fabrication method of microfluidic devices with micrometer-sized constrictions used for electrodeless dielectrophoresis (eDEP) is demonstrated here. A structure on a commercial printed circuit board (PCB) template of one-sided copper clad fiberglass-epoxy laminate was used as a molding master for polydimethylsiloxane (PDMS) soft lithography. This was achieved by printing a constriction-based microchannel pattern on glossy paper with a micrometer-scaled resolution laser printer and transferring it to the laminate’s Cu face, rendering a microstructure of ∼17 µm height and various widths across tips. The Cu master’s pattern was transferred to PDMS, and smooth constrictions were observed under the microscope. Following air plasma encapsulation, PDMS chips were loaded with an inactivated bacterial sample of fluorescently stained Brucella abortus vaccine strain S-19 and connected to an amplified voltage source to examine the sample’s response to electric field variations. After an AC/DC electric field was applied to the bacterial solution in the microfluidic device, the combined effect of electrokinetic + hydrodynamic mechanisms that interact near the dielectric microconstrictions and exert forces to the sample was observed and later confirmed by COMSOL simulations. Our fabrication method is an alternative to be used when there is no access to advanced microfabrication facilities and opens ways for target selection and preconcentration of intracellular pathogens as well as sample preparation for metagenomics.
Implementacion y comparación de sistemas dosimetricos en la evaluacion de QA paciente especifico para la tecnica VMAT en el Hospital Mexico en Costa Rica
(2024-07-05) Hincapie Hernández, Leonel; Campos Garcia, Juan Pablo
Los avances acelerados de la radioterapia con métodos de tratamiento más avanzados como IMRT y VMAT, exigen una evolución de forma conjunta de la protección radiológica con el fin de contar cada día con sistemas de dosimetría paciente específico cada vez más robustos y precisos, que permitan comprobar que las dosis planificadas son efectivamente las que se entregarán al paciente en el equipo emisor de radiación. Se implementó un nuevo sistema de dosimetría paciente especifico en el Hospital México de Costa Rica, con películas radiocrómicas EBT3 para la evaluación de planes de tratamientos IMRT y VMAT complejos. Para la implementación de este sistema de dosimetría paciente específico se utilizó TC anónimas del paquete computacional eclipse de Varian, el acelerador lineal Halcyon, se planificaron 5 planes de próstata con el método VMAT, se realizó el análisis de dosimetría paciente específico no solo con las películas radiocrómicas si no también con los dos sistemas existentes en el servicio de radioterapia del Hospital México, el portal dosimetry y el Matrixx resolution. Con la implementación de las películas radiocrómicas EBT3 se evaluaron los planes de próstata realizados y además se evaluaron los otros dos sistemas de dosimetría en el servicio de radioterapia. Se pudo desarrollar un protocolo estructurado de la implementación de la dosimetría paciente específico con películas radiocrómicas, protocolo en marcado en tres componentes: protocolo para la corrección lateral, protocolo para el cálculo de las curva de respuesta y protocolo para el análisis y comparación de dosis. La verificación se realizó mediante el análisis gamma en los tres sistemas de dosimetría paciente específico, Portal dosimetry, Matrixx resolution y Películas radiocrómicas. Se encontró una buena concordancia en los tres sistema y se puedo observar las mismas discrepancias en un plan de verificación tanto en el Matrixx resolution como en las películas radiocrómicas, garantizando así que los sistema se encuentran dentro de los márgenes de incertidumbre aceptable para ser utilizado a nivel clínico como un paquete conjunto de dosimetría paciente específico.
Estimation of Primary and Scatter Signal Profiles in Computer Tomography using Geant4
(2024-06-11) Arroyo Portilla, Daniel José; Porras Chaverri, Mariela
A method to obtain the scatter signal profiles from a commercially available computer tomography scanner, using Geant4 a Monte Carlo toolkit for C++ to create a code that mimics the most important structures of the scanner, like the bowtie filter, detecting el- ements and septa. A uniform water phantom with different diameters can be placed at the isocenter to study the scatter generated and the attenuation of the signal in the de- tecting structure. The signal characterization algorithm finds the last photon interaction before reaching a detecting element to assign based on the volume scatter profiles. Simulations without the phantom show that the crosstalk signal is between 1% and 2% of the total signal for both source energies and collimations, the septa scatter signal is lower but at the edges of each detecting module surpassing the bowtie and air signal contributions, the bowtie signal is about 0.1% of the air scan in the central module and up to 2% when moving away from the center of the detecting structure. Simulations with the phantom present show a total attenuation in the detecting struc- ture of from 2% for the smaller phantom up to 0.14% for the biggest one. Phantom scat- ter varies with the source energy and collimation, contributing up to 5% with a 320mm diameter phantom. Normalized scatter profiles can help to understand the effect of the phantom signal in a projection, simulations with all the scanner structures present and simulations where the bowtie and/or anti-scatter grid is missing can show the impact of the structures when it comes to reducing the scatter signal. Also, small signal contributions from the scanner structures and the air can be identified and assessed to see the impact on the total signal. The code developed successfully mimics the scatter signal of a CT scanner and separates it into the different scatter sources from the phantom to the scanner structures and air.
Análisis de métricas de calidad de imagen en equipos de radiología digital dentro de un programa de control de calidad remoto y automatizada
(2024) Soto Chinchilla, Yerry Alberto; Mora Rodríguez, Patricia
Se realizó un estudio cuyo propósito fue investigar la correlación entre métricas de calidad de imagen para equipos digitales de mamografía y radiología, para ello se creó una página web que almacenara las métricas y mostrara los cambios en el tiempo mediante gráficos de control, asimismo, se utilizaron rangos intercuartílicos para determinar si hubo valores que salieron de una banda de dos desviaciones estándar alrededor de la media en una distribución normal. Las métricas de calidad de imagen se extrajeron de un total de 163 imágenes para radiología convencional desde el 6 de junio de 2017 hasta el 25 de marzo de 2021 abarcando un antes y después de cambiar el tubo de rayos X y 144 de mamografía desde el 5 de junio de 2017 hasta el 26 de junio de 2020 abarcando un cambio de detector en el mamógrafo. También se obtuvo de dichas imágenes sus mapas de varianza. Los resultados muestran que las métricas que arrojan diferencias significativas para el caso de radiología convencional fueron la Relación Señal Ruido (SNR) e índice de sensibilidad (d') y para mamografía se evidencian dichas diferencias en las métricas Relación Diferencia de Señal Ruido (SDNR), Relación Señal Ruido e Índice de Sensibilidad (d'), además en virtud del análisis temporal de los mapas de varianza se comprobó que en mamografía existía fatiga del equipo que pueden provocar la existencia de artefactos que se manifiesten en el futuro que podrían llegar a ser significativos en imágenes médicas cuando se requiera la búsqueda de pequeños objetos.
First Magnetohydrodynamic Simulations of Jets and Radiative Feedback from a Massive Star
(2024-05) Barquero Alvarado, Joshua; Frutos Alfaro, Francisco
The study of massive protostars requires the explicit use of numerical simulations that allow us to follow the early stages of events defining the evolution of these stellar objects. This project aims to understand the complex processes occurring within the accretion material falling onto the star and the various dynamics within the molecular cloud. To achieve this, we utilize the state-of-the-art program known as PLUTO, combined with modules enabling us to solve the equations for magnetohydrodynamics, radiation, photoionization, and self-gravity. Consequently, we conduct our study to comprehend the impact of these modules on the star by running different simulations with alternating modules enabled. Finally, we compare the changes these modules induce in the star’s evolution and the final properties of the massive star. Protostellar outflows alone limit stellar mass growth in an accretion scenario with a finite mass reservoir. Radiative feedback dominates the latter stages of stellar formation around the zero-age main sequence. Specifically, we observe that radiation forces restrain gravitational infall toward the disk, affect the magneto-gravito-centrifugal equilibrium, and completely halt stellar accretion, resulting in a star with a mass of approximately 40 M⊙ at around 100 kyr. While photoionization widens the bipolar outflow cavities and reduces the gravitational infall momentum by about 50%, it does not limit stellar mass accretion until later stages, resulting in a star with a mass of approximately 45 M⊙ at around 120 kyr. In contrast, simulations that do not implement radiative interactions from these modules continue to accrete material at this time, and we report masses of approximately 75 M⊙ when negleting radiative force feedback.

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