196 research outputs found
The Potential of Intrinsically Magnetic Mesenchymal Stem Cells for Tissue Engineering
No full textThe magnetization of mesenchymal stem cells (MSC) has the potential to aid tissue engineering approaches by allowing tracking, targeting, and local retention of cells at the site of tissue damage. Commonly used methods for magnetizing cells include optimizing uptake and retention of superparamagnetic iron oxide nanoparticles (SPIONs). These appear to have minimal detrimental effects on the use of MSC function as assessed by in vitro assays. The cellular content of magnetic nanoparticles (MNPs) will, however, decrease with cell proliferation and the longer-term effects on MSC function are not entirely clear. An alternative approach to magnetizing MSCs involves genetic modification by transfection with one or more genes derived from Magnetospirillum magneticum AMB-1, a magnetotactic bacterium that synthesizes single-magnetic domain crystals which are incorporated into magnetosomes. MSCs with either or mms6 and mmsF genes are followed by bio-assimilated synthesis of intracytoplasmic magnetic nanoparticles which can be imaged by magnetic resonance (MR) and which have no deleterious effects on MSC proliferation, migration, or differentiation. The stable transfection of magnetosome-associated genes in MSCs promotes assimilation of magnetic nanoparticle synthesis into mammalian cells with the potential to allow MR-based cell tracking and, through external or internal magnetic targeting approaches, enhanced site-specific retention of cells for tissue engineering
An extension of the localist representation theory: grandmother cells are also widely used in the brain
No full textabstract: Based on considerable neurophysiological evidence, Roy (2012) proposed the theory that localist representation is widely used in the brain, starting from the lowest levels of processing. Grandmother cells are a special case of localist representation. In this article, I present the theory that grandmother cells are also widely used in the brain. To support the proposed theory, I present neurophysiological evidence and an analysis of the concept of grandmother cells. Konorski (1967) first predicted the existence of grandmother cells (he called them “gnostic” neurons)—single neurons that respond to complex stimuli such as faces, hands, expressions, objects, and so on. The term “grandmother cell” was introduced by Jerry Lettvin in 1969 (Barlow, 1995).View the article as published at http://journal.frontiersin.org/article/10.3389/fpsyg.2013.00300/ful
Correspondence to Joseph E. Lowery from Asim Israel, August 29, 1986
No full textA letter to Joseph E. Lowery from Asim Israel of the House of Israel requesting assistance in contacting Louis Stokes, Jesse Jackson, and Reverend Clay Evans to convince the Guyana government to release David Hill from prison. 1 page.The Atlanta University Center Robert W. Woodruff Library acknowledges the generous support of the Joseph & Evelyn Lowery Institute for Justice and Human Rights, the Joseph Echols Lowery Irrevocable Trust, and other donors in supporting the processing and digitization of Morehouse College's Joseph Echols and Evelyn Gibson Lowery Collection
Biosynthesis of magnetic nanoparticles by human mesenchymal stem cells following transfection with the magnetotactic bacterial gene mms6
No full textThe use of stem cells to support tissue repair is facilitated by loading of the therapeutic cells with magnetic nanoparticles (MNPs) enabling magnetic tracking and targeting. Current methods for magnetizing cells use artificial MNPs and have disadvantages of variable uptake, cellular cytotoxicity and loss of nanoparticles on cell division. Here we demonstrate a transgenic approach to magnetize human mesenchymal stem cells (MSCs). MSCs are genetically modified by transfection with the mms6 gene derived from Magnetospirillum magneticum AMB-1, a magnetotactic bacterium that synthesises single-magnetic domain crystals which are incorporated into magnetosomes. Following transfection of MSCs with the mms6 gene there is bio-assimilated synthesis of intracytoplasmic magnetic nanoparticles which can be imaged by MR and which have no deleterious effects on cell proliferation, migration or differentiation. The assimilation of magnetic nanoparticle synthesis into mammalian cells creates a real and compelling, cytocompatible, alternative to exogenous administration of MNPs.</p
Responsible conduct and documentation of research: a standard operating procedure template that can be customized
No full textIf you have comments or suggestions for improvements, please direct these to the corresponding author, Catherine Hayward ([email protected]).This standard operating procedure (SOP) document was prepared as a template that individual researchers can customize for their own use. Prior to publication, this SOP underwent peer review by the McMaster University Faculty of Health Sciences Research Council. The Council has endorsed the publication of this SOP to encourage researchers to develop procedures that encourage best research practices and can be customized to meet specific needs.
Should you decide to customize this SOP for your own use, please acknowledge the original authors, who include Ms. D’Andra Parker and Mr. Asim Soomro (graduate students in the Hayward laboratory). All items highlighted in yellow in the SOP must be customized.
This procedure outlines the steps involved in proper recording keeping in the laboratory. This SOP applies any/all data generated while in the laboratory, and any/all the laboratory records
Measuring microfinance access : building on existing cross-country data
No full textGiven the acknowledged need for a new effort to expand the set of available data on direct access to financial services, including a focus on access by those at low income, Honohan provides a selective review of the diverse sources of data that exist and considers how best to build on them. He proposes a basic framework within which to consider the analysis of the interesting questions: (1) How does access affect poverty and productivity? and (2) What hinders access? The author discusses existing and potential contribution of household and business user surveys, surveys of providers and their regulators, and surveys of experts, and assesses their relative strengths.Banks&Banking Reform,Environmental Economics&Policies,Health Economics&Finance,Poverty Assessment,Governance Indicators
Protection Against Lipopolysacharide-Induced Myocardial Dysfunction in Mice by Cardiac-Specific Expression of Soluble Fas
No full textThe mechanisms responsible for myocardial dysfunction in the setting of sepsis remain undefined. Fas ligation with its cognate ligand (FasL) induces apoptosis and activates cellular inflammatory responses associated with tissue injury. We determined whether interruption of Fas/FasL interaction by cardiac-specific expression of soluble Fas (sFas), a competitive inhibitor of FasL, would improve myocardial dysfunction and inflammation in a lipopolysacharide (LPS)-induced mouse model of sepsis. Wild-type (WT) and sFas transgenic mice were injected intraperitoneally with 10 mg/kg LPS or with an equivalent volume of saline. At 18 h after LPS administration, echocardiographic evaluation revealed a significant decrease in left ventricular fractional shortening in the WT mice, whereas the fractional shortening was preserved in the sFas mice. Activation of nuclear factor-kappa B (NF-κB) and the increase in the transcript levels of proinflammatory cytokines, tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and IL-6 resulting from LPS treatment were attenuated in the myocardium of sFas mice. sFas expression also inhibited LPS-induced upregulation of Toll-like receptor 4 (TLR-4) and inducible nitric oxide synthase (iNOS), and formation of peroxynitrite in the myocardium. LPS-induced increase in caspase-3/7 activity and apoptotic cell death were suppressed in sFas mice compared with WT mice. LPS-induced lung injury and increase in lung water content were also significantly reduced in sFas mice. These data indicate that neutralization of FasL by expression of sFas significantly preserves cardiac function and reduces inflammatory responses in the heart, suggesting that Fas/FasL signaling pathway is important in mediating the deleterious effects of LPS on myocardial function
X-ray and gamma-ray timing of GRB 180720B, GRB 181222B, GRB 211211A, and GRB 220910A observed with Fermi and ASIM
No full textWe present a timing study of the gamma and X-ray observations and analysis of a sample of bright gamma-ray bursts (GRBs;
i.e. GRB 180720B, GRB 181222B, GRB 211211A, and GRB 220910A), including the very bright and long GRB 211211A
(a.k.a. kilonova candidate). They have been detected and observed by the Atmosphere–Space Interactions Monitor (ASIM)
installed on the International Space Station (ISS) and the Gamma-ray Burst Monitor (GBM) onboard the Fermi mission. The
early (T − T0≈ s) and high-energy (0.3–20 MeV) ASIM High Energy Detector (HED) and (150 keV–30 MeV) Fermi (BGO)
light curves show well-defined peaks with a low quasi-periodic oscillation (QPO) frequency between 2.5 and 3.5 Hz that could
be identified with the spin of the neutron star (NS) in the binary mergers originating these GRBs. These QPOs consist on the first
detection of low-frequency QPOs (≤10 Hz) detected in magnetars so far. We also detect a strong QPO at 21.8 − 22 Hz in GRB
181222B together with its (less significant) harmonics. The low-frequency QPO would correspond to the signal of the orbiting
NS previous to the final coalescence giving rise to the gravitational wave (GW) signal. © 2025 The Author(s).MCG acknowledges S. Xiao, M. Marisaldi, and A. Mezentsev for useful discussions and feedback. MCG acknowledges financial support from the Spanish Ministry project MCI/AEI/PID2023-149817OB-C31. RSR, YDH, MCG, SG, IPG, EJFG, RGB, MPV, and AJCT acknowledge financial support from the Spanish Ministry project PID2023-151905OB-I00 and the Severo Ochoa grant CEX2021-001131-S funded by MICIU/AEI/10.13039/501100011033. RG and SBP acknowledge BRICS grant DST/IMRCD/BRICS/PilotCall1 /ProFCheap/2017(G) for the financial support. RG and SBP also acknowledge the financial support of ISRO under AstroSat archival Data utilization programme (DS
2B-13013(2)/1/2021-Sec.2). RG was sponsored by the National Aeronautics and Space Administration (NASA) through a contract with ORAU. AJCT acknowledges support from the Junta de Andalucia Project P20
01068. MM, AL, AM, and NØ acknowledge financial support from the Research Council of Norway under Contracts 208028/F50 and 223252/F50 (CoE). This research has used data obtained through the HEASARC Online Service, provided by the NASA-GSFC, in support of NASA High Energy Astrophysics Programs. The NASA’s FGST (Fermi) mission is an astrophysics and particle physics partnership, developed in collaboration with the U.S. Department of Energy, along with important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden, and the United States. ASIM is a mission of ESA’s SciSpace programme for scientific utilization of the ISS and non-ISS space exploration platforms and space environment analogues. ASIM and the ASIM Science Data Centre are funded by ESA and by national grants of Denmark, Norway, and Spain.With funding from the Spanish government through the "Severo Ochoa Centre of Excellence" accreditation (CEX2021-001131-S).Peer reviewe
Analysis of nighttime streamer corona discharges in storm clouds with ASIM data
No full textTesis del Departamento de Sistema Solar del Instituto de Astrofísica de Andalucía. Leída en el Salón de Actos del IAA el 17 de marzo del 2023, a las 12:00 h .[EN] The main objective of this doctoral thesis is to exhaustively study the corona-type
electrical discharges that take place in storm clouds. Corona discharges are characterized,
among other things, by transient optical emissions in the near ultraviolet and visible blue
range (280 - 450 nm). This is why they have been called Blue LUminous Events (BLUEs).
This thesis presents the first worldwide nighttime climatology of corona discharges in
storm clouds by combining two years of BLUEs data recorded by MMIA instrument of
ASIM on-board the ISS (Neubert et al., 2019).
This doctoral thesis focuses on investigating the physics of BLUEs, with the aim of un-
derstanding their nature and determining the mechanisms that produce them. Addition-
ally, the thesis addresses the detailed analysis of the geographic and seasonal distribution
of BLUEs is addressed from two years of unique data obtained by the Modular Multispec-
tral Imaging Array (MMIA) of the European Space Agency’s (ESA) Atmosphere Space
Interaction Monitor (ASIM) instrument that was launched into space on April 18, 2018
and has been operational at the International Space Station (ISS) since then. MMIA has
three fast photometers (100 kHz) and two cameras. The photometers have interferential
filters centered on the wavelengths 337.0 nm (with a width of 4 nm), 777.4 nm (with a
width of 5 nm) and a wide filter between 180 nm and 230 nm. The two available cameras
use filters centered at 337.0 nm and 777.4 nm with the same characteristics as the light
meter filters.
The doctoral thesis is presented as a collection of three scientific articles in which I
am the first author. These articles have been published in high-impact journals in the
field of atmospheric sciences (atmospheric electricity). The articles are preceded by a
thesis index, a summary (in Spanish and English), an introduction, the motivation of
the studies carried out, a brief description of the methodology that has been followed
and a concise presentation of the BLUEs.
In my first article (published in Journal of Geophysical Research - Atmospheres, 2020,
and highlighted by the editor) the structure of the BLUEs is described based on the
observations of a storm recorded by ASIM on May 14, 2019 over Indonesia. The events
were observed using the 337.0 nm photometer, during periods of little or no concurrent
activity in the photometer centered on the 777.4 nm band (which is typical for lightning
optical emissions). Through radio measurements made from the ground, it was concludedthat 7 of the 10 cases analyzed corresponded to positive narrow bipolar events (NBE).
NBEs are characterized by being very strong radio frequency (RF) pulses with three
important features: (1) their very short duration (about 20 microseconds), (2) a bipolar
appearance (very fast rise and fall of two radio pulses of positive and negative polarity
or vice versa) of the waveform in the VLF / LF frequency range (10 - 400 kHz) and (3)
followed by extremely powerful bursts of radiation. on VHF / HF (3 - 300 MHz).
NBEs, when detected in the VLF/LF range, are typically ten times more intense than
radio emissions in the high frequency (HF) range typically emitted by normal intracloud
and/or intercloud lightning.. In addition, recent observations (2016 and 2017) suggest
that NBEs are the result of very fast processes of electrical breakdown in air. Fast
breakdown is associated to cold electrical discharges, that is, those that do not heat the
surrounding air (unlike normal lightning) and in which the temperature of the ambient
electrons reaches very high values of up to 80000 ◦C (about 7 eV) (electron volts). The
fact that electrons have a small mass (2000 times lighter than the lightest atom) prevents
them from heating the surrounding air.
In this first work, a new and innovative method was developed to determine the height
of BLUEs in storm clouds from the analysis of their optical signals. In particular, the
method is based on fitting the 337.0 nm light curves captured by the MMIA 337.0 nm
photometer to a model of light diffusion in storm clouds. The height obtained agrees well
with measurements carried out with methods based on ground-based radio detection.
The altitude at which these NBEs occur ranges between 8.5 km and 14 km. Obser-
vations indicate that single-pulse blue flashes are caused by streamers (air plasma darts
with strong head ionization) which, as discussed above, do not heat the air (they are cold
discharges). The findings discussed in the first paper led us to conclude that positive
NBEs are corona discharges made up of hundreds of millions of positive streamers (the
head of the streamer carries positive electrical charge) that form in thunderclouds and
that the BLUEs are the optical manifestation of the NBEs.
My second article (published in Geophysical Research Letters, 2021), focuses on the
global analysis of the blue pulses observed in storm clouds, focusing on studying the
relationship of the BLUEs with lightning, both annually and seasonally. For this, a
new algorithm has been developed and used to be able to filter the raw information
from MMIA, and systematically obtain only the activity of BLUEs, excluding the rest
of electrical interactions in storm clouds. The result of this comprehensive work is the
first, and so far the only, nocturnal climatology of BLUEs (corona discharge activity
in storm clouds) obtained from data from the ASIM MMIA instrument. Our research
concluded that approximately 11 BLUEs occur globally every second at local midnight,
and the average number of BLUEs on land/sea is 7 to 4. Geographically, the peak ofthe distribution of BLUEs is located in a region in northwestern Colombia. Three main
zones of atmospheric electrical activity are shown in this distribution: America, Europe
/ Africa, and Asia / Australia. A zone of weaker BLUE electrical activity has also been
found in the Pacific.
My third paper (published in Journal of Geophysical Research - Atmospheres, 2022)
delves into the results of the second, and focuses on distinguishing different types of
blue pulses based on the goodness of their fit with the ”first hitting model” or FHM
(model of diffusion of light in storm clouds) and in extracting its main characteristics
such as optical power density (μW m−2) of the 337.0 nm pulse maximum, rise time of
maximum, total duration, brightness, etc, based on the fit and raw data. In addition, we
also found two types of global distributions of BLUEs, depending on whether an extra
criteria is applied (or not) to the algorithm of the previous work (paper two) on the
South Atlantic Magnetic Anomaly (SAA). This additional criteria is included because
a clear oversensing of cosmic rays was observed with ASIM in the SAA region. The
extra criteria aims to limit the number of cosmic rays detected by putting a limit on
the duration of the events detected in the SAA. It is concluded that the real number of
BLUEs would range between the two distributions found in this third work. The analysis
of the characteristics of the BLUEs indicates that around 10% of the events are clearly
BLUEs with a clear maximum. Most of them have a peak optical power density below 25
μW/m2, occur up to 4 km below the upper cloud boundary and are made up of hundreds
of millions of streamers (up to 3 × 109).[ES] El objetivo de esta tesis doctoral es estudiar de forma exhaustiva las descargas el ́ectricas
de tipo corona que tienen lugar en las nubes de tormenta. Las descargas corona se
caracterizan, entre otras cosas, por emitir luz en el rango ultravioleta cercano y azul (280
- 450 nm). Es por esto por lo que se las ha llamado Blue LUminous Events (BLUEs). Esta
tesis presenta la primera climatolog ́ıa nocturna de descargas de corona en las nubes de
tormenta combinando dos a ̃nos de datos de BLUEs recogidos por el instrumento MMIA
de ASIM a bordo de la ISS (Neubert et al., 2019).
La tesis se centra en, por un lado, investigar la f ́ısica de los BLUEs, esto es, en descifrar
su naturaleza y en determinar cu ́ales son los mecanismos que los producen. Por otra
lado, se aborda el an ́alisis detallado de la distribuci ́on geogr ́afica y estacional de los
BLUEs a partir de dos a ̃nos de datos obtenidos por el Modular Multispectral Imaging
Array (MMIA) del instrumento Atmosphere Space Interaction Monitor (ASIM) de la
Agencia Espacial Europea (ESA) que fue lanzado al espacio el 18 de abril de 2018 y que
est ́a operativo en la Estaci ́on Espacial Internacional (ISS) desde entonces. MMIA est ́a
formado por tres fot ́ometros r ́apidos (100 kHz) y dos c ́amaras. Los fot ́ometros disponen
de filtros interferenciales centrados en las longitudes de onda 337.0 nm (con una anchura
de banda de 4 nm), 777.4 nm (con una anchura de banda de 5 nm) y un filtro ancho
entre 180 nm y 230 nm. Las dos c ́amaras disponibles usan filtros centrados en 337.0 nm
y 777.4 nm con las mismas caracter ́ısticas que los filtros de los fot ́ometros.
La tesis doctoral se presenta como una colecci ́on de tres art ́ıculos cient ́ıficos en los que
soy primer autor. Estos art ́ıculos sobre electricidad atmosf ́erica han sido publicados en
revistas de alto impacto en el campo de las ciencias atmosf ́ericas. Los art ́ıculos vienen
precedidos por un ́ındice de la tesis, un resumen (en espa ̃nol e ingl ́es), una introducci ́on,
la motivaci ́on de los estudios realizados, una breve descripci ́on de la metodolog ́ıa que se
ha seguido y una descripci ́on concisa de los BLUEs.
En mi primer art ́ıculo (publicado en Journal of Geophysical Research - Atmospheres,
2020, y destacado por su editor) se describe la estructura de los BLUEs apoy ́andose en
las observaciones de una tormenta registrada por ASIM el 14 de Mayo de 2019 sobre
Indonesia. Los eventos fueron observados con el fot ́ometro 337.0 nm, sin actividad con-
currente, o despreciable en el fot ́ometro centrado en la banda 777.4 nm (emisiones t ́ıpicas
de rayos). A trav ́es de mediciones de radio efectuadas desde el suelo, se concluy ́o que 7de los 10 casos analizados correspond ́ıan a eventos bipolares estrechos positivos o positive
narrow bipolar events (NBE) en ingl ́es. Los NBEs se caracterizan por ser pulsos muy
fuertes de radiofrecuencia (RF) con tres rasgos importantes: (1) su muy corta duraci ́on
(apenas 20 microsegundos), (2) un aspecto bipolar (muy r ́apida subida y bajada de dos
pulsos de radio de polaridad positiva y negativa o viceversa) de la forma de onda en el
rango de frecuencias VLF / LF (10 - 400 kHz) y (3) por venir habitualmente seguidos
de potent ́ısimos estallidos de radiaci ́on VHF / HF (3 - 300 MHz).
Los NBE detectados en el rango VLF / LF son por lo general diez veces m ́as intensos
que las emisiones de radio en el rango de alta frecuencia (HF) procedentes de rayos
normales intranube o entre nubes. Adem ́as, observaciones recientes (2016 y 2017) parecen
sugerir que los NBEs son el resultado de procesos muy r ́apidos de ruptura el ́ectrica
del aire t ́ıpicos de descargas el ́ectricas fr ́ıas, esto es, aquellas que no calientan el aire
circundante (al contrario que los rayos normales) y en las que la temperatura de los
electrones ambientales alcanzan valores muy elevados de hasta 80000 ◦C (unos 7 eV
[electr ́on voltios]). El hecho de que los electrones tengan una masa muy peque ̃na (2000
veces m ́as ligeros que el ́atomo m ́as liviano) impide que, a ́un siendo muy energ ́eticos,
puedan calentar el aire circundante.
En este primer trabajo se desarroll ́o un nuevo y novedoso m ́etodo para determinar la
altura de los BLUEs en las nubes de tormenta a partir del an ́alisis de sus se ̃nales ́opticas.
En particular, el m ́etodo se basa en ajustar las curvas de luz captadas por el fot ́ometro
centrado en 337.0 nm de MMIA a un modelo de difusi ́on de luz en las nubes de tormenta.
La altura obtenida concuerda bien con medidas realizadas con m ́etodos basados en radio
detecci ́on.
La altitud a la que ocurren estos NBEs se sit ́ua aproximadamente entre 8.5 y 14 km.
Las observaciones indican que los flashes azules con un solo pulso son originados por
streamers (dardos de plasma de aire con fuerte ionizaci ́on en la cabeza) que, como se ha
mencionado, no calientan el aire, esto es, son descargas fr ́ıas, la luz emitida por streamers
es pues la manifestaci ́on ́optica de dichos NBEs. Los hallazgos que se discuten en el primer
trabajo nos llevaron a concluir que los NBEs positivos son descargas corona formadas
por cientos de millones de streamers positivos (la cabeza del streamer transporta carga
el ́ectrica positiva) que se forman en las nubes de tormenta y que los BLUEs son la
manisfestaci ́on ́optica de dichos NBEs.
Mi segundo art ́ıculo (publicado en Geophysical Research Letters, 2021), se centra en
el an ́alisis a nivel global de los pulsos azules observados en las nubes de tormenta, de-
teni ́endose en estudiar la relaci ́on de los BLUEs con los rayos, tanto anual como esta-
cionalmente. Para ello se ha desarrollado y utilizado un novedoso algoritmo para poder
filtrar la informaci ́on en bruto de MMIA, y obtener sistem ́aticamente s ́olo la actividadde BLUEs excluyendo el resto de interacciones el ́ectricas en las nubes de tormenta. El
resultado de este completo trabajo es la primera, y hasta ahora la ́unica, climatolog ́ıa
nocturna de BLUEs (coronas en nubes de tormenta) obtenida a partir de datos del
instrumento MMIA de ASIM. En nuestra investigaci ́on se concluy ́o que, aproximada-
mente, tienen lugar unos 11 BLUEs a nivel global cada segundo en la media noche local,
y que el promedio de BLUEs en tierra / mar es de 7 a 4. Geogr ́aficamente, el pico de
la distribuci ́on de BLUEs est ́a localizado en una regi ́on al noroeste de Colombia. En
esta distribuci ́on se muestran tres zonas principales de actividad el ́ectrica atmosf ́erica:
Am ́erica, Europa/ ́Africa, y Asia/Australia. Tambi ́en se ha encontrado una zona de ac-
tividad el ́ectrica m ́as d ́ebil en el Pac ́ıfico.
Mi tercer trabajo (publicado en Journal of Geophysical Research - Atmospheres, 2022)
profundiza en los resultados del segundo, y se centra en distinguir distintos tipos de
pulsos azules en funci ́on de la bondad de su ajuste con el ”first hitting model” ́o FHM
(modelo de difusi ́on de luz en las nubes) y en obtener sus principales caracter ́ısticas tales
como densidad de potencia ́optica (μW m−2) del m ́aximo del pulso 337.0 nm, tiempo
de subida del m ́aximo, duraci ́on total, brillo, etc, con base al ajuste y a los datos en
bruto. Adem ́as, tambi ́en encontramos dos tipos de distribuciones globales de BLUEs,
dependiendo de si se aplica (o no) un criterio extra al algoritmo del anterior trabajo en
la anomal ́ıa magn ́etica del Atlantico Sur (SAA). Este criterio adicional se incluye debido
que se observ ́o una clara sobredetecci ́on de rayos c ́osmicos con ASIM en la zona de la
SAA. El criterio extra pretende limitar el n ́umero de rayos c ́osmicos detectados poniendo
un l ́ımite en la duraci ́on de los eventos detectados en la SAA. Se estima que la cifra
real de BLUEs se hallar ́a entre las dos distribuciones encontradas en este ́ultimo trabajo.
El an ́alisis de las caracter ́ısticas de los BLUEs nos indica que alrededor del 10% de los
eventos son claramente BLUEs con un m ́aximo claro. La mayor ́ıa de ellos tiene una
densidad de potencia ́optica por unidad de superficie de pico por debajo de 25 μW/m2,
ocurren a una distancia de hasta 4 km por debajo del l ́ımite superior de la nube y est ́an
formados por cientos de millones de streamers (hasta 3 × 109).This thesis was supported by the Spanish Ministry of Science and Innovation, Min-
isterio de Ciencia e Innovaci ́on (AEI) under project ESP2017-86263-C4-4-R, PID2019-
109269RB-C43 and the FEDER program. I acknowledge a PhD research contract through
the project ESP2017-86263-C4-4-R and I also acknowledge financial support from the
State Agency for Research of the Spanish MCIU through the “Center of Excellence
Severo Ochoa” award for the Instituto de Astrof ́ısica de Andaluc ́ıa (SEV-2017-0709).Peer reviewe
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