Soft γ-ray repeaters exhibit bursting emission in hard X-rays and soft γ-rays. During the active phase, they emit random short (milliseconds to several seconds long), hard-X-ray bursts, with peak ...luminosities
of 10
to 10
erg per second. Occasionally, a giant flare with an energy of around 10
to 10
erg is emitted
. These phenomena are thought to arise from neutron stars with extremely high magnetic fields (10
to 10
gauss), called magnetars
. A portion of the second-long initial pulse of a giant flare in some respects mimics short γ-ray bursts
, which have recently been identified as resulting from the merger of two neutron stars accompanied by gravitational-wave emission
. Two γ-ray bursts, GRB 051103 and GRB 070201, have been associated with giant flares
. Here we report observations of the γ-ray burst GRB 200415A, which we localized to a 20-square-arcmin region of the starburst galaxy NGC 253, located about 3.5 million parsecs away. The burst had a sharp, millisecond-scale hard spectrum in the initial pulse, which was followed by steady fading and softening over 0.2 seconds. The energy released (roughly 1.3 × 10
erg) is similar to that of the superflare
from the Galactic soft γ-ray repeater SGR 1806-20 (roughly 2.3 × 10
erg). We argue that GRB 200415A is a giant flare from a magnetar in NGC 253.
It is researched a wide class of parametric estimations of power spectral density based on principle of entropy maximum and autoregression observation model. At that there is distinguished the key ...parameter which is used model order. It is considered a problem of a priori uncertainty when true value of order is a priori unknown. It is proposed a new criterion for definition of order using finite sampling volume with purpose of overcome of the drawbacks of existing algorithms in conditions of small sampling. The principle of guaranteed significance level in a problem of complex statistic hypothesis verification is a basic principle of this criterion. In contrast to criteria of AIC, BIC, etc. this criterion is not related to determination of measurements inaccuracy, since it uses a conception of “significance level” of formed solution only. The efficiency of proposed criterion is researched theoretically and experimentally. An example of its application in a problem of spectral analysis of voice signals is considered. Recommendations about its practical application in the systems of digital signal processing are given.
On 2019 April 25.346 and 26.640 UT the Laser Interferometer Gravitational-Wave Observatory (LIGO) and Virgo gravitational-wave (GW) observatory announced the detection of the first candidate events ...in Observing Run 3 that contained at least one neutron star (NS). S190425z is a likely binary neutron star (BNS) merger at dL = 156 41 Mpc, while S190426c is possibly the first NS-black hole (BH) merger ever detected, at dL = 377 100 Mpc, although with marginal statistical significance. Here we report our optical follow-up observations for both events using the MMT 6.5 m telescope, as well as our spectroscopic follow-up of candidate counterparts (which turned out to be unrelated) with the 4.1 m SOAR telescope. We compare to publicly reported searches, explore the overall areal coverage and depth, and evaluate those in relation to the optical/near-infrared (NIR) kilonova emission from the BNS merger GW170817, to theoretical kilonova models, and to short gamma-ray burst (SGRB) afterglows. We find that for a GW170817-like kilonova, the partial volume covered spans up to about 40% for S190425z and 60% for S190426c. For an on-axis jet typical of SGRBs, the search effective volume is larger, but such a configuration is expected in at most a few percent of mergers. We further find that wide-field γ-ray and X-ray limits rule out luminous on-axis SGRBs, for a large fraction of the localization regions, although these searches are not sufficiently deep in the context of the γ-ray emission from GW170817 or off-axis SGRB afterglows. The results indicate that some optical follow-up searches are sufficiently deep for counterpart identification to about 300 Mpc, but that localizations better than 1000 deg2 are likely essential.
Two types of constitutive equations accounting for the stress mode and the loosening of the material during elastoplastic deformation are considered. The constitutive equations of one type include ...two nonlinear relationships between the first invariants of the stress and strain tensors and between the second invariants of the deviator tensors and include the third invariant of the stress deviator. The constitutive equations of the other type use equivalence stress containing the first and second invariants of the stress tensor. Literature experimental data for tubular isotropic specimens under tension, compression, torsion, and internal pressure are used for assessing the loosening of the material.
•Matrix conversion provides a high productivity and low cost of syngas production.•Kinetic modeling revealed three characteristic stages of methane matrix conversion.•Acetylene is the most problem ...impurity at matrix conversion of methane.•Important role of acetylene steam reforming in the post-flame zone.•Steam reforming of products in the last two stages increases yields of H2 and CO.
The conversion of natural gas to syngas is a key and most expensive stage of modern gas chemical technologies. As a promising alternative to existing technologies, a non-catalytic matrix conversion of natural gas to syngas was proposed. However, the reaction products, in addition to CO and H2, also contain unreacted methane, CO2 and acetylene. The latter is the most problem impurity, as it is a precursor of soot and other heavy products. In this work, the kinetic analysis of changes in the composition of the products during the matrix conversion of rich methane-air mixtures up to the establishment of the thermodynamic equilibrium was carried out. Three characteristic stages of the process were identified. The first stage of fast reactions involving oxygen is completed in a very short time (∼10−2 s at 1500 K) with almost complete oxygen consumption and the formation of CO, H2, CO2, H2O and some minor products of methane pyrolysis, mainly acetylene, but at their ratio, far from equilibrium. At the second stage, slow reactions of steam reforming of the formed products significantly increase the amount of hydrogen. The ratio CO2H2COH2O reaches an equilibrium value, but not the concentration of individual products due to incomplete conversion of acetylene and methane. At the third and longest stage, the system reaches equilibrium, and acetylene is not among the equilibrium products. The results of kinetic modeling and experimental study of partial oxidation of methane in matrix-type reformers have shown the important role of acetylene steam conversion in the post-flame zone. This reaction leads to a substantial decrease of methane and acetylene with a simultaneous increase in the yields of hydrogen and CO.
The problem statement is given and the algorithm for solving problems of plasticity for axisymmetric bodies made of isotropic materials with properties depending on a stress mode and plastic ...loosening is described. The constitutive equations of the theory of deformation processes along the trajectories of small curvature containing two nonlinear dependences are used. One of them implements the relationship between the first invariants of stress and strain tensors, and the other one implements the relationship between the second invariants of the corresponding deviators. The effect of the dependence of deformation curves on the stress mode and the plastic change in the bulk strain on the results of calculating the stress-strain state of the shell is studied.
This article introduces the novel technique to reduce the computation time for classifying a sequence of observations (frames), such as a video stream, where each observation is described by ...high-dimensional embeddings extracted by a deep neural network. By using the methodology of granular computing, an observed sequence is represented at various scales using different frame rates. The coarse-grained granule is described as an aggregation (mean pooling) of deep embeddings of an object from a few frames extracted with a low frame rate. A descriptor for a fine-grained granule is computed using the embeddings of most frames. The classifiers are learned for every granularity level. At the classification phase, the coarse-grained descriptor of the input sequence is fed into the first classifier, and the classes with high confidence scores fill a positive set from three-way decisions. The decision-making procedure is terminated at a granularity level for which the only one category is included in its positive set or the last fine-grained granule is reached. It is experimentally shown for the video-based facial expression recognition problem that our technique is up to 30 times faster than traditional processing of all frames without significant accuracy degradation.
ABSTRACT Using observations of the INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL), we place upper limits on the gamma-ray and hard X-ray prompt emission associated with the gravitational ...wave event GW150914, which was discovered by the LIGO/Virgo Collaboration. The omnidirectional view of the INTEGRAL/SPI-ACS has allowed us to constrain the fraction of energy emitted in the hard X-ray electromagnetic component for the full high-probability sky region of LIGO triggers. Our upper limits on the hard X-ray fluence at the time of the event range from erg cm−2 to erg cm−2 in the 75 keV-2 MeV energy range for typical spectral models. Our results constrain the ratio of the energy promptly released in gamma-rays in the direction of the observer to the gravitational wave energy E E . We discuss the implication of gamma-ray limits for the characteristics of the gravitational wave source, based on the available predictions for prompt electromagnetic emission.
Jasmonates are plant hormones that are involved in the regulation of different aspects of plant life, wherein their functions and molecular mechanisms of action in wheat are still poorly studied. ...With the aim of gaining more insights into the role of jasmonic acid (JA) in wheat growth, development, and responses to environmental stresses, we have generated transgenic bread wheat plants overexpressing
(
), one of the key genes of the JA biosynthesis pathway. Analysis of transgenic plants showed that
overexpression affects wheat development, including germination, growth, flowering time, senescence, and alters tolerance to environmental stresses. Transgenic wheat plants with high
expression levels have increased basal levels of JA, and up-regulated expression of
, a jasmonate biosynthesis pathway gene that is known to be regulated by a positive feedback loop that maintains and boosts JA levels. Transgenic wheat plants with high
expression levels are characterized by delayed germination, slower growth, late flowering and senescence, and improved tolerance to short-term freezing. The work demonstrates that genetic modification of the jasmonate pathway is a suitable tool for the modulation of developmental traits and stress responses in wheat.
Abstract
Swift J1818.0−1607 is a radio-loud magnetar with a spin period of 1.36 s and a dipolar magnetic field strength of
B
∼ 3 × 10
14
G, which is very young compared to the Galactic pulsar ...population. We report here on the long-term X-ray monitoring campaign of this young magnetar using XMM-Newton, NuSTAR, and Swift from the activation of its first outburst in 2020 March until 2021 October, as well as INTEGRAL upper limits on its hard X-ray emission. The 1–10 keV magnetar spectrum is well modeled by an absorbed blackbody with a temperature of
kT
BB
∼ 1.1 keV and apparent reduction in the radius of the emitting region from ∼0.6 to ∼0.2 km. We also confirm the bright diffuse X-ray emission around the source extending between ∼50″ and ∼110″. A timing analysis revealed large torque variability, with an average spin-down rate
ν
̇
∼
−2.3 × 10
−11
Hz
2
that appears to decrease in magnitude over time. We also observed Swift J1818.0−1607 with the Karl G. Jansky Very Large Array on 2021 March 22. We detected the radio counterpart to Swift J1818 measuring a flux density of
S
v
= 4.38 ± 0.05 mJy at 3 GHz and a half-ringlike structure of bright diffuse radio emission located at ∼90″ to the west of the magnetar. We tentatively suggest that the diffuse X-ray emission is due to a dust-scattering halo and that the radio structure may be associated with the supernova remnant of this young pulsar, based on its morphology.
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