3,983 research outputs found
Numerical study of synchrotron and inverse-Compton radiation from gamma-ray burst afterglows with decaying microturbulence
The multiwavelength observations of GRB afterglows, together with some
high-performance particle-in-cell simulations, hint that the magnetic field may
decay behind the shock front. In this work, we develop a numerical code to
calculate the evolution of the accelerated electron distribution, their
synchrotron and inverse-Compton (IC) spectra and accordingly the light curves
(LCs) under the assumption of decaying microturbulence (DM) downstream of the
shock, with the fluid proper
time since injection. We find: (1) The synchrotron spectrum in the DM model is
similar to that in the homogeneous turbulence (HT) model with very low magnetic
field strength. However, the difference in the IC spectral component is
relatively more obvious between them, due to the significant change of the
postshock electron energy distribution with DM. (2) If the magnetic field decay
faster, there are less electrons cool fast, and the IC spectral component
becomes weaker. (3) The LCs in the DM model decay steeper than in the HT model,
and the spectral evolution and the LCs in the DM model is similar to the HT
model where the magnetic field energy fraction decreases with observer time,
. (4) The DM model can naturally
produce a significant IC spectral component in TeV energy range, but due to the
Klein-Nishina suppression the IC power cannot be far larger than the
synchrotron power. We apply the DM model to describe the afterglow data of GRB
190114C and find the magnetic field decay exponent and the
electron spectral index . Future TeV observations of the IC emission
from GRB afterglows will further help to probe the poorly known microphysics of
relativistic shocks.Comment: 14 pages, 9 figures, 3 tables, submitted to MNRAS, comments welcom
Similarity Analysis of Projectile Penetration into Concrete
This paper presents a dimensionless model for the depth of penetration (DOP) of a projectile penetrating into a concrete target, based on the similarity theory involving intermediate asymptotics, complete similarity, and incomplete similarity. The calculated numerical results are in good agreement with previous experimental data, including two sets of full-scale and twenty-four sets of sub-scale penetration of non-deformable projectiles into concrete targets. Moreover, compared with several empirical and semi-empirical DOP models, the new model is applicable within a relatively broader range, including the penetration of both sub-scale and full-scale projectiles. For the limitations of the validity, dimensionless parameters Π3 = ϕt/ϕ larger than 12, Π4 = (ϕ3fc)/(Mv02) smaller than 0.1, and the initial impact velocity of the projectile less than about 900 to 1000m/s are necessary for the model
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