28,984 research outputs found
The dependence of tidal stripping efficiency on the satellite and host galaxy morphology
In this paper we study the tidal stripping process for satellite galaxies
orbiting around a massive host galaxy, and focus on its dependence on the
morphology of both satellite and host galaxy. For this purpose, we use three
different morphologies for the satellites: pure disc, pure bulge and a mixture
bulge+disc. Two morphologies are used for the host galaxies: bulge+disc and
pure bulge. We find that while the spheroidal stellar component experiences a
constant power-law like mass removal, the disc is exposed to an exponential
mass loss when the tidal radius of the satellite is of the same order of the
disc scale length. This dramatic mass loss is able to completely remove the
stellar component on time scale of 100 Myears. As a consequence two satellites
with the same stellar and dark matter masses, on the same orbit could either
retain considerable fraction of their stellar mass after 10 Gyrs or being
completely destroyed, depending on their initial stellar morphology. We find
that there are two characteristic time scales describing the beginning and the
end of the disc removal, whose values are related to the size of the disc. This
result can be easily incorporated in semi-analytical models. We also find that
the host morphology and the orbital parameters also have an effect on the
determining the mass removal, but they are of secondary importance with respect
to satellite morphology. We conclude that satellite morphology has a very
strong effect on the efficiency of stellar stripping and should be taken into
account in modeling galaxy formation and evolution.Comment: 11 pages, 9 figures; accepted for publication in MNRA
Adaptive and Robust Fault-Tolerant Tracking Control of Contact force of Pantograph-Catenary for High-Speed Trains
Abstract This paper presents a modified multi-body dynamic model and a linear time-invariant model with actuator faults (loss of effectiveness faults, bias faults) and matched and unmatched uncertainties. Based on the fault model, a class of adaptive and robust tracking controllers are proposed which are adjusted online to tolerate the time-varying loss of effectiveness faults and bias faults, and compensate matched disturbances without the knowledge of bounds. For unmatched uncertainties, optimal control theory is added to the controller design processes. Simulations on a pantograph are shown to verify the efficiency of the proposed fault-tolerant design approach
Pattern Division Multiple Access with Large-scale Antenna Array
In this paper, pattern division multiple access with large-scale antenna
array (LSA-PDMA) is proposed as a novel non-orthogonal multiple access (NOMA)
scheme. In the proposed scheme, pattern is designed in both beam domain and
power domain in a joint manner. At the transmitter, pattern mapping utilizes
power allocation to improve the system sum rate and beam allocation to enhance
the access connectivity and realize the integration of LSA into multiple access
spontaneously. At the receiver, hybrid detection of spatial filter (SF) and
successive interference cancellation (SIC) is employed to separate the
superposed multiple-domain signals. Furthermore, we formulate the sum rate
maximization problem to obtain the optimal pattern mapping policy, and the
optimization problem is proved to be convex through proper mathematical
manipulations. Simulation results show that the proposed LSA-PDMA scheme
achieves significant performance gain on system sum rate compared to both the
orthogonal multiple access scheme and the power-domain NOMA scheme.Comment: 6 pages, 5 figures, this paper has been accepted by IEEE VTC
2017-Sprin
Central mass and luminosity of Milky Way satellites in the LCDM model
It has been pointed out that the Galactic satellites all have a common mass
around 1e7 Msun within 300 pc (M03), while they span almost four order of
magnitudes in luminosity (Mateo et al. 1993, Strigari et al. 2008). It is
argued that this may reflect a specific scale for galaxy formation or a scale
for dark matter clustering. Here we use numerical simulations coupled with a
semi-analytic model for galaxy formation, to predict the central mass and
luminosity of galactic satellites in the LCDM model. We show that this common
mass scale can be explained within the Cold Dark Matter scenario when the
physics of galaxy formation is taken into account. The narrow range of M03
comes from the narrow distribution of circular velocities at time of accretion
(peaking around 20 km/s) for satellites able to form stars and the not tight
correlation between halo concentration and circular velocity. The wide range of
satellite luminosities is due to a combination of the mass at time of accretion
and the broad distribution of accretion redshifts for a given mass. This causes
the satellites baryonic content to be suppressed by photo-ionization to very
different extents. Our results favor the argument that the common mass M03
reflects a specific scale (circular velocity ~ 20 km/s) for star formation.Comment: 5 pages, 3 figures. References added, discussion enlarged, new
version of Figure 3. Minor changes to match the version accepted for
publication on ApJ Letter
β-catenin ameliorates myocardial infarction by preventing YAP-associated apoptosis
Objective: To explore whether the effect of β-catenin on MI and MI-induced cardiomyocyte apoptosis is YAP-dependent.
Methods: The authors established an MI rat model by ligating the anterior descending branch of the left coronary artery, and an MI cell model by treating cardiomyocytes with H2O2.
Results: β-catenin downregulation was observed in MI cardiac tissues and in H2O2-treated cardiomyocytes. Lentiviral-CTNNB1 was administered to MI rats to upregulate β-catenin expression in MI cardiac tissue. β-catenin recovery reduced the myocardial infarct area, fibrosis, and apoptotic cell death in MI rats. H2O2 treatment attenuated cell viability and induced cell death in cardiomyocytes, whereas β-catenin overexpression partially reversed these changes. Moreover, H2O2 treatment caused the deactivation of Yes-Associated Protein (YAP), as detected by increased YAP phosphorylation and reduced the nuclear localization of YAP. Upregulation of β-catenin expression reactivated YAP in H2O2-treated cardiomyocytes. Reactivation of YAP was achieved by administration of Mitochonic Acid-5 (MA-5) to H2O2-treated cardiomyocytes, and deactivation of YAP by CIL56 treatment in β-catenin-overexpressing H2O2-treated cardiomyocytes. MA-5 administration increased cell viability and repressed apoptosis in H2O2-treated cardiomyocytes, whereas CIL56 treatment counteracted the effects of β-catenin overexpression on cell survival and apoptosis.
Conclusions: The present data indicate that β-catenin and YAP are effective treatment targets for MI, blocking the apoptotic death of cardiomyocytes
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