1,021 research outputs found
A Search For Supernova Remnants in The Nearby Spiral Galaxy M74 (NGC 628)
We have identified nine new SNR candidates in M74 with [S II]/H
0.4 as the basic criterion. We obtain [S II]/H ratio in the
range from 0.40 to 0.91 and H intensities from 2.8
erg cm s to 1.7 erg cm s. We
also present spectral follow-up observations of the SNR candidates and can
confirm only three of them (SNR2, SNR3, and SNR5). The lack of confirmation for
the rest might be due to the contamination by the nearby H II emission regions
as well as due to the inaccurate positioning of the long slit on these objects.
In addition, we search the Observatory archival data for the X-ray
counterparts to the optically identified candidates. We find positional
coincidence with only three SNR candidates, SNR1, SNR2, and SNR8. The spectrum
of SNR2 yields a shock temperature of 10.8 keV with an ionization timescale of
1.6 10 s cm indicating a relatively young remnant in an
early Sedov phase which is not supported by our optical wavelength analysis.
Given the high luminosity of 10 erg s and the characteristics of
the X-ray spectrum, we favor an Ultra Luminous X-ray Source interpretation for
this source associated with an SNR. We calculate an X-ray flux upper limit of
9.0 erg cm s for the rest of the SNRs
including spectroscopically identified SNR3 and SNR5.Comment: 10 pages, 8 figures, accepted to be published in A&
Radio light curves during the passage of cloud G2 near Sgr A*
We calculate radio light curves produced by the bow shock that is likely to
form in front of the G2 cloud when it penetrates the accretion disk of Sgr A*.
The shock acceleration of the radio-emitting electrons is captured
self-consistently by means of first-principles particle-in-cell simulations. We
show that the radio luminosity is expected to reach maximum in early 2013,
roughly a month after the bow shock crosses the orbit pericenter. We estimate
the peak radio flux at 1.4 GHz to be 1.4 - 22 Jy depending on the assumed orbit
orientation and parameters. We show that the most promising frequencies for
radio observations are in the 0.1<nu<1 GHz range, for which the bow shock
emission will be much stronger than the intrinsic radio flux for all the models
considered.Comment: 15 pages, 10 figures, accepted for publication in MNRA
Hard turning with variable micro-geometry PcBN tools
Cataloged from PDF version of article.This paper presents investigations on hard turning with variable edge design PcBN inserts. Turning of
hardened AISI 4340 steel with uniform and variable edge design PcBN inserts is conducted, forces and
tool wear are measured. 3D finite element modelling is utilized to predict chip formation, forces,
temperatures and tool wear on uniform and variable edge micro-geometry tools. Predicted forces and
tool wear contours are compared with experiments. The temperature distributions and tool wear
contours demonstrate the advantages of variable edge micro-geometry design.
2008 CIRP
Finite-temperature extension for cold neutron star equations of state
Observations of isolated neutron stars place constraints on the equation of
state (EOS) of cold, neutron-rich matter, while nuclear physics experiments
probe the EOS of hot, symmetric matter. Many dynamical phenomena, such as
core-collapse supernovae, the formation and cooling of proto-neutron stars, and
neutron star mergers, lie between these two regimes and depend on the EOS at
finite temperatures for matter with varying proton fractions. In this paper, we
introduce a new framework to accurately calculate the thermal pressure of
neutron-proton-electron matter at arbitrary density, temperature, and proton
fraction. This framework can be expressed using a set of five
physically-motivated parameters that span a narrow range of values for
realistic EOS and are able to capture the leading-order effects of degenerate
matter on the thermal pressure. We base two of these parameters on a new
approximation of the Dirac effective mass, with which we reproduce the thermal
pressure to within <~30% for a variety of realistic EOS at densities of
interest. Three additional parameters, based on the behavior of the symmetry
energy near the nuclear saturation density, allow for the extrapolation of any
cold EOS in beta-equilibrium to arbitrary proton fractions. Our model thus
allows a user to extend any cold nucleonic EOS, including piecewise-polytropes,
to arbitrary temperature and proton fraction, for use in calculations and
numerical simulations of astrophysical phenomena. We find that our formalism is
able to reproduce realistic finite-temperature EOS with errors of <~20% and
offers a 1-3 orders-of-magnitude improvement over existing ideal-fluid models.Comment: Accepted for publication in Ap
Hybrid Thermal-Nonthermal Synchrotron Emission from Hot Accretion Flows
We investigate the effect of a hybrid electron population, consisting of both
thermal and non-thermal particles, on the synchrotron spectrum, image size, and
image shape of a hot accretion flow onto a supermassive black hole. We find two
universal features in the emitted synchrotron spectrum: (i) a prominent
shoulder at low (< 10^11 Hz) frequencies that is weakly dependent on the shape
of the electron energy distribution, and (ii) an extended tail of emission at
high (> 10^13 Hz) frequencies whose spectral slope depends on the slope of the
power-law energy distribution of the electrons. In the low-frequency shoulder,
the luminosity can be up to two orders of magnitude greater than with a purely
thermal plasma even if only a small fraction (< 1%) of the steady-state
electron energy is in the non-thermal electrons. We apply the hybrid model to
the Galactic center source, Sgr A*. The observed radio and IR spectra imply
that at most 1% of the steady-state electron energy is present in a power-law
tail in this source. This corresponds to no more than 10% of the electron
energy injected into the non-thermal electrons and hence 90% into the thermal
electrons. We show that such a hybrid distribution can be sustained in the flow
because thermalization via Coulomb collisions and synchrotron self-absorption
are both inefficient. The presence of non-thermal electrons enlarges the size
of the radio image at low frequencies and alters the frequency dependence of
the brightness temperature. A purely thermal electron distributions produces a
sharp-edged image while a hybrid distribution causes strong limb brightening.
These effects can be seen up to frequencies ~10^11 Hz and are accessible to
radio interferometers.Comment: 33 pages with figures, to appear in the Astrophysical Journa
Interactions mechanism of commonly used drugs for the treatment of Covid-19
In this study conformation analysis of seven drugs commonly used in the treatment of COVID-19 was performed. The most stable conformers of the drug molecules were used as initial data for docking analysis. Using the Cavityplus program, the probable most active binding sites of both apo and holo forms of COVID-19 main protease enzyme (Mpro) and spike glycoprotein of SARSCoV-2 receptors were determined. The interaction mechanisms of the 7 FDA approved drugs (arbidol, colchicine, dexamethasone, favipiravir, galidesivir, hydroxychloroquine, remdesivir) were examined using the AutoDock Vina program. The six of the seven drugs were found to be more stable in binding to apo form of COVID-19 Mpro and spike glycoprotein. Moreover, a set of molecular mechanics (MM) Poisson-Boltzmann (PB) surface area (SA) calculations on the investigated drugs-protein systems were performed and the estimated binding free energy of remdesivir and the apo form of Mpro system was found to be the best. The interaction results of FDA drugs with the apo form of COVID-19 Mpro and spike glycoprotein can play an important role for the treatment of COVID-19.
KEY WORDS: COVID-19, Drugs, Molecular modelling, Conformational analysis, Molecular docking
Bull. Chem. Soc. Ethiop. 2020, 34(3), 613-623.
DOI: https://dx.doi.org/10.4314/bcse.v34i3.1
Anisotropic Emission from Multilayered Plasmon Resonator Nanocomposites of Isotropic Semiconductor Quantum Dots
Cataloged from PDF version of article.We propose and demonstrate a nanocomposite localized surface plasmon resonator
embedded into an artificial three-dimensional construction. Colloidal semiconductor quantum dots
are assembled between layers of metal nanoparticles to create a highly strong plasmon-exciton
interaction in the plasmonic cavity. In such a multilayered plasmonic resonator architecture of
isotropic CdTe quantum dots, we observed polarized light emission of 80% in the vertical
polarization with an enhancement factor of 4.4, resulting in a steady-state anisotropy value of
0.26 and reaching the highest quantum efficiency level of 30% ever reported for such CdTe quantum
dot solids. Our electromagnetic simulation results are in good agreement with the experimental
characterization data showing a significant emission enhancement in the vertical polarization, for
which their fluorescence decay lifetimes are substantially shortened by consecutive replication of our
unit cell architecture design. Such strongly plasmon-exciton coupling nanocomposites hold great
promise for future exploitation and development of quantum dot plasmonic biophotonics and
quantum dot plasmonic optoelectronics
Rapid and Precise Determination of Zero-Field Splittings by Terahertz Time-Domain Electron Paramagnetic Resonance Spectroscopy
Zero-field splitting (ZFS) parameters are fundamentally tied to the
geometries of metal ion complexes. Despite their critical importance for
understanding the magnetism and spectroscopy of metal complexes, they are not
routinely available through general laboratory-based techniques, and are often
inferred from magnetism data. Here we demonstrate a simple tabletop
experimental approach that enables direct and reliable determination of ZFS
parameters in the terahertz (THz) regime. We report time-domain measurements of
electron paramagnetic resonance (EPR) signals associated with THz-frequency
ZFSs in molecular complexes containing high-spin transition-metal ions. We
measure the temporal profiles of the free-induction decays of spin resonances
in the complexes at zero and nonzero external magnetic fields, and we derive
the EPR spectra via numerical Fourier transformation of the time-domain
signals. In most cases, absolute values of the ZFS parameters are extracted
from the measured zero-field EPR frequencies, and the signs can be determined
by zero-field measurements at two different temperatures. Field-dependent EPR
measurements further allow refined determination of the ZFS parameters and
access to the g-factor. The results show good agreement with those obtained by
other methods. The simplicity of the method portends wide applicability in
chemistry, biology and material science.Comment: 36 pages, 30 figures, 1 tabl
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