3,085 research outputs found
Modified evolution of stellar binaries from supermassive black hole binaries
The evolution of main sequence binaries resided in the galactic centre is
influenced a lot by the central super massive black hole (SMBH). Due to this
perturbation, the stars in a dense environment are likely to experience mergers
or collisions through secular or non-secular interactions. In this work, we
study the dynamics of the stellar binaries at galactic center, perturbed by
another distant SMBH. Geometrically, such a four-body system is supposed to be
decomposed into the inner triple (SMBH-star-star) and the outer triple
(SMBH-stellar binary-SMBH). We survey the parameter space and determine the
criteria analytically for the stellar mergers and the tidal disruption events
(TDEs). For a relative distant and equal masses SMBH binary, the stars have
more opportunities to merge as a result from the Lidov-Kozai(LK) oscillations
in the inner triple. With a sample of tight stellar binaries, our numerical
experiments reveal that a significant fraction of the binaries, ~70 per cent,
experience merger eventually. Whereas the majority of the stellar TDEs are
likely to occur at a close periapses to the SMBH, induced by the outer Kozai
effect. The tidal disruptions are found numerically as many as ~10 per cent for
a close SMBH binary that is enhanced significantly than the one without the
external SMBH. These effects require the outer perturber to have an inclined
orbit (>=40 degree) relatively to the inner orbital plane and may lead to a
burst of the extremely astronomical events associated with the detection of the
SMBH binary.Comment: 12 pages, 9 figures, MNRAS in pres
Negative feedback effects on star formation history and cosmic reionization
After considering the effects of negative feedback on the process of star
formation, we explore the relationship between star formation process and the
associated feedback, by investigating how the mechanical feedback from
supernovae(SNe) and radiative feedback from luminous objects regulate the star
formation rate and therefore affect the cosmic reionization.Based on our
present knowledge of the negative feedback theory and some numerical
simulations, we construct an analytic model in the framework of the Lambda cold
dark matter model. In certain parameter regions, our model can explain some
observational results properly. In large halos(T_vir>10000 K), both mechanical
and radiative feedback have a similar behavior: the relative strength of
negative feedback reduces as the redshift decreases. In contrast, in small
halos (T_vir<10000 K$) that are thought to breed the first stars at early time,
the radiative feedback gets stronger when the redshift decreases. And the star
formation rate in these small halos depends very weakly on the star-formation
efficiency. Our results show that the radiative feedback is important for the
early generation stars. It can suppress the star formation rate considerably.
But the mechanical feedback from the SNe explosions is not able to affect the
early star formation significantly. The early star formation in small-halo
objects is likely to be self-regulated. The radiative and mechanical feedback
dominates the star formation rate of the PopII/I stars all along. The feedback
from first generation stars is very strong and should not be neglected.
However, their effects on the cosmic reionization are not significant, which
results in a small contribution to the optical depth of Thomson scattering.Comment: 12 pages,6 figure
The State-of-the-art of Coordinated Ramp Control with Mixed Traffic Conditions
Ramp metering, a traditional traffic control strategy for conventional
vehicles, has been widely deployed around the world since the 1960s. On the
other hand, the last decade has witnessed significant advances in connected and
automated vehicle (CAV) technology and its great potential for improving
safety, mobility and environmental sustainability. Therefore, a large amount of
research has been conducted on cooperative ramp merging for CAVs only. However,
it is expected that the phase of mixed traffic, namely the coexistence of both
human-driven vehicles and CAVs, would last for a long time. Since there is
little research on the system-wide ramp control with mixed traffic conditions,
the paper aims to close this gap by proposing an innovative system architecture
and reviewing the state-of-the-art studies on the key components of the
proposed system. These components include traffic state estimation, ramp
metering, driving behavior modeling, and coordination of CAVs. All reviewed
literature plot an extensive landscape for the proposed system-wide coordinated
ramp control with mixed traffic conditions.Comment: 8 pages, 1 figure, IEEE INTELLIGENT TRANSPORTATION SYSTEMS CONFERENCE
- ITSC 201
Correlation effects for semiconducting single wall carbon nanotube: a density matrix renormalization group study
In this paper, we report the applicability of the density matrix
renormalization group(DMRG) approach to the cylindrical single wall carbon
nanotube (SWCN) for purpose of its correlation effect. By applying the DMRG
approach to the ++ model, with and being the hopping and
Coulomb energies between the nearest neighboring sites, respectively, and
the onsite Coulomb energy, we calculate the phase diagram for the SWCN with
chiral numbers (), which reflects the competition between the
correlation energy and . Within reasonable parameter ranges, we
investigate possible correlated groundstates, the lowest excitations and the
corresponding correlation functions in which the connection with the excitonic
insulator is particularly addressed.Comment: 1 source files, 5 figure
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