90 research outputs found
Classifying globular clusters and applying them to estimate the mass of the Milky Way
We combine the kinematics of 159 globular clusters (GCs) provided by the Gaia
Early Data Release 3 (EDR3) with other observational data to classify the GCs,
and to estimate the mass of the Milky Way (MW). We use the age-metallicity
relation, integrals of motion, action space and the GC orbits to identify the
GCs as either formed in-situ (Bulge and Disk) or ex situ (via accretion). We
find that have formed in situ, may be related to known merger
events: Gaia-Sausage-Enceladus, the Sagittarius dwarf galaxy, the Helmi
streams, the Sequoia galaxy, and the Kraken galaxy. We also further identify
three new sub-structures associated with the Gaia-Sausage-Enceladus. The
remaining of GCs are unrelated to the known mergers and thought to be
from small accretion events. We select 46 GCs which have radii kpc
and obtain the anisotropy parameter , which is
lower than the recent result using the sample of GCs in Gaia Data Release 2,
but still in agreement with it by considering the error bar. By using the same
sample, we obtain the MW mass inside the outermost GC as , and the corresponding
. The estimated mass is
consistent with the results in many recent studies. We also find that the
estimated and mass depend on the selected sample of GCs. However, it is
difficult to determine whether a GC fully traces the potential of the MW.Comment: 32 pages, 11 figures, Accepted to RA
Classifying globular clusters and applying them to estimate the mass of the Milky Way
We combine the kinematics of 159 globular clusters (GCs) provided by the Gaia
Early Data Release 3 (EDR3) with other observational data to classify the GCs,
and to estimate the mass of the Milky Way (MW). We use the age-metallicity
relation, integrals of motion, action space and the GC orbits to identify the
GCs as either formed in-situ (Bulge and Disk) or ex situ (via accretion). We
find that have formed in situ, may be related to known merger
events: Gaia-Sausage-Enceladus, the Sagittarius dwarf galaxy, the Helmi
streams, the Sequoia galaxy, and the Kraken galaxy. We also further identify
three new sub-structures associated with the Gaia-Sausage-Enceladus. The
remaining of GCs are unrelated to the known mergers and thought to be
from small accretion events. We select 46 GCs which have radii kpc
and obtain the anisotropy parameter , which is
lower than the recent result using the sample of GCs in Gaia Data Release 2,
but still in agreement with it by considering the error bar. By using the same
sample, we obtain the MW mass inside the outermost GC as , and the corresponding
. The estimated mass is
consistent with the results in many recent studies. We also find that the
estimated and mass depend on the selected sample of GCs. However, it is
difficult to determine whether a GC fully traces the potential of the MW.Comment: 32 pages, 11 figures, Accepted to RA
Slope Position Rather Than Thinning Intensity Affects Arbuscular Mycorrhizal Fungi (AMF) Community in Chinese Fir Plantations
Background and Objectives: Arbuscular mycorrhizal fungi (AMF) play a crucial role in individual plant capability and whole ecosystem sustainability. Chinese fir, one of the most widely planted tree species in southern China, forms associations with AMF. However, it is still unclear what impacts thinning management applied to Chinese fir plantations has on the structure and diversity of soil AMF communities. This research attempts to bridge this knowledge gap.
Materials and Methods: A thinning experiment was designed on different slope positions in Chinese fir plantations to examine the impacts of slope position and thinning intensity on colonization, diversity, and community composition of AMF.
Results: Our research showed that the altitudinal slope position had significant effects on colonization, diversity, and community composition of AMF in Chinese fir plantations. In addition, the interaction between slope position and thinning intensity had significant effects on AMF diversity. Colonization by AMF on the lower slope position was significantly higher than on the upper slope position, while AMF diversity on the upper slope position was higher than on the middle and lower slope positions. Glomus was the most abundant genus in all slope positions, especially on the middle and lower slope positions. The relative abundance of Diversispora was significantly different among slope positions with absolute dominance on the upper slope position. Scutellospora was uniquely found on the upper slope position. Furthermore, soil Mg and Mn contents and soil temperature positively affected AMF community composition at the operational taxonomic unit (OTU) level. Conclusions: These findings suggested that slope position should be considered in the management of Chinese fir plantations. Furthermore, both chemical fertilization and AMF augmentation should be undertaken on upper hill slope positions as part of sustainable management practices for Chinese fir plantations
A Fast Transient Backend to Detect FRBs with the Tianlai Dish Pathfinder Array
The Tianlai Dish Pathfinder array is a radio interferometer array consisting
of 16 six meter dish antennas. The original digital backend integration time is
at the seconds level, designed for HI intensity mapping experiment. A new
digital backend with millisecond response is added to enable it to search for
fast radio burst (FRB) during its observations. The design and calibration of
this backend, and the real time search pipeline for it are described in this
paper. It is capable of forming 16 digital beams for each linear polarisation,
covering an area of 19.6 square degrees. The search pipeline is capable of
searching for, recording and classifying FRBs automatically in real time. In
commissioning, we succeeded in capturing the signal pulses from the pulsars PSR
B0329+54 and B2021+51.Comment: 16 pages, 14 figures, RAA accepte
Probing lepton flavor violation signal via e+ e- (gamma gamma) ---> l(i) anti-l(j) in the littlest Higgs model with T-parity at the ILC
In the littlest Higgs model with T-parity, the new interactions between the
mirror leptons and the Standard Model leptons can induce some lepton flavor
violation (LFV) processes at loop level. We study the possibility of the ILC to
probe the LFV production processes . Our results show that the rates of can reach 1 fb in optimal cases after reasonable kinematical
cuts, which implies that these processes may be observed at the ILC
Forecasting the Dark Energy Measurement with Baryon Acoustic Oscillations: Prospects for the LAMOST surveys
The Large Area Multi-Object Spectroscopic Telescope (LAMOST) is a dedicated
spectroscopic survey telescope being built in China, with an effective aperture
of 4 meters and equiped with 4000 fibers. Using the LAMOST telescope, one could
make redshift survey of the large scale structure (LSS). The baryon acoustic
oscillation (BAO) features in the LSS power spectrum provide standard rulers
for measuring dark energy and other cosmological parameters. In this paper we
investigate the meaurement precision achievable for a few possible surveys: (1)
a magnitude limited survey of all galaxies, (2) a survey of color selected red
luminous galaxies (LRG), and (3) a magnitude limited, high density survey of
z<2 quasars. For each survey, we use the halo model to estimate the bias of the
sample, and calculate the effective volume. We then use the Fisher matrix
method to forecast the error on the dark energy equation of state and other
cosmological parameters for different survey parameters. In a few cases we also
use the Markov Chain Monte Carlo (MCMC) method to make the same forecast as a
comparison. The fiber time required for each of these surveys is also
estimated. These results would be useful in designing the surveys for LAMOST.Comment: Replaced with version accepted by MNRA
Associated production of neutral toppion with a pair of heavy quarks in collisions
We have studied a neutral toppion production process in the topcolor-assisted technicolor(TC2) model. We
find that the cross section of is much
larger than that of . On the other hand,
the cross section can be obviously enhanced with the increasing of c.m.energy.
With GeV, the cross section of production can
reach the level of a few fb. The results show that is the most ideal channel to detect
neutral toppion due to the clean SM background. With such sufficient signals
and clean background, neutral toppion could be detected at TESLA with high
c.m.energy.Comment: 11 pages, 5 figure
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