154 research outputs found
Particle Acceleration in Relativistic Electron-positron Jets with Helical Magnetic Fields
The properties of relativistic jets, their interaction with the ambient
environment and particle acceleration due to kinetic instabilities are studied
self-consistently with Particle-in-Cell (PIC) simulations. In this work we
study how a relativistic electron-positron jet containing a helical magnetic
field evolves by focusing on its interaction with the external ambient plasma.
Particularly, 3D PIC simulations are performed using a longer simulation system
than previous studies with an embedded helical magnetic field. An important key
issue in this work is how such a magnetic field affects an electron-positron
jet and how this excites kinetic instabilities such as the Weibel instability
(WI), the kinetic Kelvin-Helmholtz instability (kKHI) and others by further
focusing on how particles accelerate. We do find that kinetic instabilities
along with generated magnetic turbulence are present and consequently
accelerate particles. At the linear stage we observe recollimation-like
features at the center of the simulated jet and later-on as the
electron-positron jet evolves, the magnetic fields generated by the
instabilities become untangled and reorganized into a new topology near the
non-linear phase. We additionally report indications of reconnection near the
end of the non-linear stage, before the magnetic-field becomes untangled, as
electrons get accelerated by multiple magnetic islands in the jet. In the
present study the untangled magnetic field becomes turbulent without any
reformation as it happened in our previous study of an electron-proton jet,
which we will use to additionally compare the present results, obtaining
important insights about the nature of these phenomena applicable to
high-energy astrophysical environments such as Active Galactic Nuclei jets and
Gamma-ray bursts.Comment: 12 pages, 24 figures, submitted to MNRAS Journa
Δ<sup>9</sup>-tetrahydrocannabinol and 2-AG decreases neurite outgrowth and differentially affects ERK1/2 and Akt signaling in hiPSC-derived cortical neurons
Endocannabinoids regulate different aspects of neurodevelopment. In utero exposure to the exogenous psychoactive cannabinoid Δ9-tetrahydrocannabinol (Δ9-THC), has been linked with abnormal cortical development in animal models. However, much less is known about the actions of endocannabinoids in human neurons. Here we investigated the effect of the endocannabinoid 2-arachidonoyl glycerol (2AG) and Δ9-THC on the development of neuronal morphology and activation of signaling kinases, in cortical neurons derived from human induced pluripotent stem cells (hiPSCs). Our data indicate that the cannabinoid type 1 receptor (CB1R), but not the cannabinoid 2 receptor (CB2R), GPR55 or TRPV1 receptors, is expressed in young, immature hiPSC-derived cortical neurons. Consistent with previous reports, 2AG and Δ9-THC negatively regulated neurite outgrowth. Interestingly, acute exposure to both 2AG and Δ9-THC inhibited phosphorylation of serine/threonine kinase extracellular signal-regulated protein kinases (ERK1/2), whereas Δ9-THC also reduced phosphorylation of Akt (aka PKB). Moreover, the CB1R inverse agonist SR 141716A attenuated the decrease in neurite outgrowth and ERK1/2 phosphorylation induced by 2AG and Δ9-THC. Taken together, our data suggest that hiPSC-derived cortical neurons express CB1Rs and are responsive to exogenous cannabinoids. Thus, hiPSC-neurons may represent a good cellular model for investigating the role of the endocannabinoid system in regulating cellular processes in developing human neurons
Competence to restart meiosis of oocytes from different follicle sizes obtained from slaughterhouse ovaries
Se evaluó la capacidad de los ovocitos de folículos según su tamaño para reiniciar la meiosis. Los folículos se midieron y clasificaron como Grupo 1 (G1 <4 mm), Grupo 2 (G2 4-8 mm) y Grupo 3 (G3 >8 mm). La aspiración se realizó por grupo con una aguja 21G conectada a una bomba de vacío, con una presión de 65 mmHg. Los complejos cúmulos de ovocitos (COC) recuperados se clasificaron como adecuados y no adecuados para la producción de embriones in vitro, de acuerdo con las características del cúmulo y del citoplasma. Los COC elegibles e inadecuados se valoraron con la prueba de azul brillante de Cresilo (BCB) y se clasificaron en BCB+ y BCB-. La maduración in vitro (IVM) se llevó a cabo en microgotas, incubadas en una cámara de CO2 al 5%, 38.5 °C y 90% de humedad durante 24 horas. La progresión meiótica se determinó por extrusión del corpúsculo polar mediante epifluorescencia bajo un microscopio invertido. La morfometría de ovocitos se estableció mediante una cámara de alta definición (Excelis AU-600-HD) y un software (AmScope v.3.7). El porcentaje de recuperación de ovocitos fue mayor de 63%. Los folículos de G2 proporcionaron un mayor porcentaje de COC elegibles (65.7%), donde el 59% de este grupo se clasificó como BCB+. Los ovocitos aptos de G1 y G2 reanudaron la meiosis en un 75%. Además, se observó que los ovocitos después de IVM redujeron su diámetro. Se concluye que los ovocitos de folículos entre 4-8 mm (G2) proporcionan un mayor porcentaje de COC maduros; sin embargo, el 50% de folículos <4 mm (G1) son una fuente prometedora de ovocitos viables, por lo que deben usarse para la producción de embriones in vitro.The competence of oocytes according to follicle size to restart meiosis was evaluated. The follicles were measured and classified as Group 1 (G1 <4 mm), Group 2 (G2 4-8 mm) and Group 3 (G3 >8 mm). The aspiration was performed by group with a 21G needle connected to a vacuum pump, with a pressure of 65 mmHg. The complex oocyte clusters (COCs) recovered were classified as suitable and unsuitable to produce embryos in vitro, according to the characteristics of the cumulus and the cytoplasm. Eligible and unsuitable COCs were assessed with the Brilliant Cresyl Blue (BCB) and were classified into BCB+ and BCB-. In vitro maturation (IVM) was carried out in microdroplets, incubated in a 5% CO2 chamber, 38.5 °C and 90% humidity for 24 hours. The meiotic progression was determined by extrusion of the polar corpuscle by epifluorescence under an inverted microscope. Oocyte morphometry was established using a high definition camera (Excelis AU-600-HD) and software (AmScope v.3.7). The recovery percentage of oocytes was greater than 63%. The G2 follicles provided a higher percentage of eligible COCs (65.7%), where 59% of this group was classified as BCB+. The fit oocytes of G1 and G2 resumed meiosis by 75%. In addition, it was observed that oocytes after IVM reduced their diameter. It is concluded that follicle oocytes between 4-8 mm (G2) provide a higher percentage of mature COCs; however, 50% of follicles <4 mm (G1) are a promising source of viable oocytes, so they should be used for in vitro embryo production
Atypical Neurogenesis in Induced Pluripotent Stem Cells From Autistic Individuals
BACKGROUND: Autism is a heterogeneous collection of disorders with a complex molecular underpinning. Evidence from postmortem brain studies have indicated that early prenatal development may be altered in autism. Induced pluripotent stem cells (iPSCs) generated from individuals with autism with macrocephaly also indicate prenatal development as a critical period for this condition. But little is known about early altered cellular events during prenatal stages in autism. METHODS: iPSCs were generated from 9 unrelated individuals with autism without macrocephaly and with heterogeneous genetic backgrounds, and 6 typically developing control individuals. iPSCs were differentiated toward either cortical or midbrain fates. Gene expression and high throughput cellular phenotyping was used to characterize iPSCs at different stages of differentiation. RESULTS: A subset of autism-iPSC cortical neurons were RNA-sequenced to reveal autism-specific signatures similar to postmortem brain studies, indicating a potential common biological mechanism. Autism-iPSCs differentiated toward a cortical fate displayed impairments in the ability to self-form into neural rosettes. In addition, autism-iPSCs demonstrated significant differences in rate of cell type assignment of cortical precursors and dorsal and ventral forebrain precursors. These cellular phenotypes occurred in the absence of alterations in cell proliferation during cortical differentiation, differing from previous studies. Acquisition of cell fate during midbrain differentiation was not different between control- and autism-iPSCs. CONCLUSIONS: Taken together, our data indicate that autism-iPSCs diverge from control-iPSCs at a cellular level during early stage of neurodevelopment. This suggests that unique developmental differences associated with autism may be established at early prenatal stages
Operations of and Future Plans for the Pierre Auger Observatory
Technical reports on operations and features of the Pierre Auger Observatory,
including ongoing and planned enhancements and the status of the future
northern hemisphere portion of the Observatory. Contributions to the 31st
International Cosmic Ray Conference, Lodz, Poland, July 2009.Comment: Contributions to the 31st ICRC, Lodz, Poland, July 200
The Pierre Auger Observatory III: Other Astrophysical Observations
Astrophysical observations of ultra-high-energy cosmic rays with the Pierre
Auger ObservatoryComment: Contributions to the 32nd International Cosmic Ray Conference,
Beijing, China, August 201
Measurement of the Depth of Maximum of Extensive Air Showers above 10^18 eV
We describe the measurement of the depth of maximum, Xmax, of the
longitudinal development of air showers induced by cosmic rays. Almost four
thousand events above 10^18 eV observed by the fluorescence detector of the
Pierre Auger Observatory in coincidence with at least one surface detector
station are selected for the analysis. The average shower maximum was found to
evolve with energy at a rate of (106 +35/-21) g/cm^2/decade below 10^(18.24 +/-
0.05) eV and (24 +/- 3) g/cm^2/decade above this energy. The measured
shower-to-shower fluctuations decrease from about 55 to 26 g/cm^2. The
interpretation of these results in terms of the cosmic ray mass composition is
briefly discussed.Comment: Accepted for publication by PR
Anisotropy and chemical composition of ultra-high energy cosmic rays using arrival directions measured by the Pierre Auger Observatory
The Pierre Auger Collaboration has reported evidence for anisotropy in the
distribution of arrival directions of the cosmic rays with energies
eV. These show a correlation with the distribution
of nearby extragalactic objects, including an apparent excess around the
direction of Centaurus A. If the particles responsible for these excesses at
are heavy nuclei with charge , the proton component of the
sources should lead to excesses in the same regions at energies . We here
report the lack of anisotropies in these directions at energies above
(for illustrative values of ). If the anisotropies
above are due to nuclei with charge , and under reasonable
assumptions about the acceleration process, these observations imply stringent
constraints on the allowed proton fraction at the lower energies
Update on the correlation of the highest energy cosmic rays with nearby extragalactic matter
Data collected by the Pierre Auger Observatory through 31 August 2007 showed
evidence for anisotropy in the arrival directions of cosmic rays above the
Greisen-Zatsepin-Kuz'min energy threshold, \nobreak{eV}. The
anisotropy was measured by the fraction of arrival directions that are less
than from the position of an active galactic nucleus within 75 Mpc
(using the V\'eron-Cetty and V\'eron catalog). An updated
measurement of this fraction is reported here using the arrival directions of
cosmic rays recorded above the same energy threshold through 31 December 2009.
The number of arrival directions has increased from 27 to 69, allowing a more
precise measurement. The correlating fraction is , compared
with expected for isotropic cosmic rays. This is down from the early
estimate of . The enlarged set of arrival directions is
examined also in relation to other populations of nearby extragalactic objects:
galaxies in the 2 Microns All Sky Survey and active galactic nuclei detected in
hard X-rays by the Swift Burst Alert Telescope. A celestial region around the
position of the radiogalaxy Cen A has the largest excess of arrival directions
relative to isotropic expectations. The 2-point autocorrelation function is
shown for the enlarged set of arrival directions and compared to the isotropic
expectation.Comment: Accepted for publication in Astroparticle Physics on 31 August 201
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