36 research outputs found
Signatures of photon and axion-like particle mixing in the gamma-ray burst jet
Photons couple to Axion-Like Particles (ALPs) or more generally to any pseudo
Nambu-Goldstone boson in the presence of an external electromagnetic field.
Mixing between photons and ALPs in the strong magnetic field of a Gamma-Ray
Burst (GRB) jet during the prompt emission phase can leave observable imprints
on the gamma-ray polarization and spectrum. Mixing in the intergalactic medium
is not expected to modify these signatures for ALP mass > 10^(-14) eV and/or
for < nG magnetic field. We show that the depletion of photons due to
conversion to ALPs changes the linear degree of polarization from the values
predicted by the synchrotron model of gamma ray emission. We also show that
when the magnetic field orientation in the propagation region is perpendicular
to the field orientation in the production region, the observed synchrotron
spectrum becomes steeper than the theoretical prediction and as detected in a
sizable fraction of GRB sample. Detection of the correlated polarization and
spectral signatures from these steep-spectrum GRBs by gamma-ray polarimeters
can be a very powerful probe to discover ALPs. Measurement of gamma-ray
polarization from GRBs in general, with high statistics, can also be useful to
search for ALPs.Comment: 17 pages, 3 figures. Accepted for publication in JCAP with minor
change
Estudo anatomorfológico, radiográfico e tomográfico de Schistosomus reflexus em ovino da raça Dorper: relato de caso
The polarized image of a synchrotron-emitting ring of gas orbiting a black hole
High Energy Astrophysic
Constraints on black-hole charges with the 2017 EHT observations of M87*
InstrumentationHigh Energy Astrophysic
The variability of the black hole image in M87 at the dynamical timescale
The black hole images obtained with the Event Horizon Telescope (EHT) are expected to be variable at the dynamical timescale near their horizons. For the black hole at the center of the M87 galaxy, this timescale (5–61 days) is comparable to the 6 day extent of the 2017 EHT observations. Closure phases along baseline triangles are robust interferometric observables that are sensitive to the expected structural changes of the images but are free of station-based atmospheric and instrumental errors. We explored the day-to-day variability in closure-phase measurements on all six linearly independent nontrivial baseline triangles that can be formed from the 2017 observations. We showed that three triangles exhibit very low day-to-day variability, with a dispersion of ∼3°–5°. The only triangles that exhibit substantially higher variability (∼90°–180°) are the ones with baselines that cross the visibility amplitude minima on the u–v plane, as expected from theoretical modeling. We used two sets of general relativistic magnetohydrodynamic simulations to explore the dependence of the predicted variability on various black hole and accretion-flow parameters. We found that changing the magnetic field configuration, electron temperature model, or black hole spin has a marginal effect on the model consistency with the observed level of variability. On the other hand, the most discriminating image characteristic of models is the fractional width of the bright ring of emission. Models that best reproduce the observed small level of variability are characterized by thin ring-like images with structures dominated by gravitational lensing effects and thus least affected by turbulence in the accreting plasmas.https://iopscience.iop.org/article/10.3847/1538-4357/ac332e/pdfPublished versio
Broadband multi-wavelength properties of M87 during the 2017 Event Horizon Telescope campaign
High Energy AstrophysicsInstrumentatio
Search for patterns by combining cosmic-ray energy and arrival directions at the Pierre Auger Observatory
Energy-dependent patterns in the arrival directions of cosmic rays are searched for using data of the Pierre Auger Observatory. We investigate local regions around the highest-energy cosmic rays with E > = 6×1019 eV by analyzing cosmic rays with energies above E > = 5×1018 eV arriving within an angular separation of approximately 15°. We characterize the energy distributions inside these regions by two independent methods, one searching for angular dependence of energy-energy correlations and one searching for collimation of energy along the local system of principal axes of the energy distribution. No significant patterns are found with this analysis. The comparison of these measurements with astrophysical scenarios can therefore be used to obtain constraints on related model parameters such as strength of cosmic-ray deflection and density of point sources
Hidden Profiles and Concealed Information: Strategic Information Sharing and Use in Group Decision Making
Estudo anatomorfológico, radiográfico e tomográfico de Schistosomus reflexus em ovino da raça Dorper: relato de caso
Schistosomus reflexus (SR) is a rare and fatal congenital anomaly, primarily observed in ruminants, presenting fetus with dorsiflexion of the vertebral column, exposure of thoracic and visceral organs, and scoliosis. A caesarian was performed on a Dorper sheep on a farm in Botucatu-SP and according to the general characteristics and findings observed in the necropsy of the fetus it was an SR case. The radiography indicated a marked ventro-dorsal deviation of the thoracolumbar column segment and deformity of the ribs. On the computed tomography the integrity of the bones and organs were detected, except for the absence of a lumbar vertebra. No data were available in the literature for SR diagnosis in sheep by image, so radiographic and tomographic exams of the fetus were done.O Schistosomus reflexus (SR) é uma anomalia congênita fatal e rara, primariamente observada em ruminantes, a qual apresenta feto com dorsoflexão da coluna vertebral, exposição das vísceras abdominais e torácicas e escoliose. Foi realizada uma cesariana de ovelha da raça Dorper, em propriedade da região de Botucatu-SP. Pelas características gerais e achados de necropsia, tratava-se de um caso de SR. A radiografia revelou acentuado desvio ventrodorsal do segmento da coluna vertebral toracolombar e deformidades das costelas. Na tomografia computadorizada, observou-se presença da integridade dos ossos e órgãos, exceto ausência de uma vértebra lombar. Não havia dados na literatura de diagnóstico por imagem de SR em ovinos, portanto procedeu-se, de forma inédita, a exames radiográfico e tomográfico do feto
Investigating 1,2,3,4,5,6-hexahydroazepino[4,3-b]indole as scaffold of butyrylcholinesterase-selective inhibitors with additional neuroprotective activities for Alzheimer's disease
Due to the role of butyrylcholinesterase (BChE)in acetylcholine hydrolysis in the late stages of the Alzheimer's disease (AD), inhibitors of butyrylcholinesterase (BChE)have been recently envisaged, besides acetylcholinesterase (AChE)inhibitors, as candidates for treating mild-to-moderate AD. Herein, synthesis and AChE/BChE inhibition activity of some twenty derivatives of 1,2,3,4,5,6-hexahydroazepino[4,3-b]indole (HHAI)is reported. Most of the newly synthesized HHAI derivatives achieved the inhibition of both ChE isoforms with IC50s in the micromolar range, with a structure-dependent selectivity toward BChE. Apparently, molecular volume and lipophilicity do increase selectivity toward BChE, and indeed the N2-(4-phenylbutyl)HHAI derivative 15d, which behaves as a mixed-type inhibitor, resulted the most potent (IC50 0.17 μM)and selective (>100-fold)inhibitor toward either horse serum and human BChE. Moreover, 15d inhibited in vitro self-induced aggregation of neurotoxic amyloid-β (Aβ)peptide and displayed neuroprotective effects in neuroblastoma SH-SY5Y cell line, significantly recovering (P < 0.001)cell viability when impaired by Aβ1-42 and hydrogen peroxide insults. Overall, this study highlighted HHAI as useful and versatile scaffold for developing new small molecules targeting some enzymes and biochemical pathways involved in the pathogenesis of AD. © 2019 Elsevier Masson SA