286 research outputs found
Determination of fundamental properties of an M31 globular cluster from main-sequence photometry
M31 globular cluster B379 is the first extragalactic cluster, the age of
which was determined by main-sequence photometry. In this method, the age of a
cluster is obtained by fitting its CMD with stellar evolutionary models.
However, different stellar evolutionary models use different parameters of
stellar evolution, such as range of stellar masses, different opacities and
equations of state, and different recipes, and so on. So, it is interesting to
check whether different stellar evolutionary models can give consistent results
for the same cluster. Brown et al. (2004a) constrained the age of B379 by
comparing its CMD with isochrones of the 2006 VandenBerg models. Using SSP
models of BC03 and its multi-photometry, Ma et al. (2007) independently
determined the age of B379, which is in good agreement with the determination
of Brown et al. (2004a). The BC03 models are calculated based on the Padova
evolutionary tracks. It is necessary to check whether the age of B379 which,
being determined based on the Padova evolutionary tracks, is in agreement with
the determination of Brown et al. (2004a). So, in this paper, we re-determine
its age using isochrones of the Padova stellar evolutionary models. In
addition, the metal abundance, the distance modulus, and the reddening value
for B379 are also determined in this paper. The results obtained in this paper
are consistent with the previous determinations, which including the age
obtained by Brown et al. (2004a). So, this paper confirms the consistence of
the age scale of B379 between the Padova isochrones and the 2006 VandenBerg
isochrones, i.e. the results' comparison between Brown et al. (2004a) and Ma et
al. (2007) is meaningful. The results obtained in this paper are: the
metallicity [M/H]=-0.325, the age Gyr, the reddening value
E(B-V)=0.08, and the distance modulus .Comment: Accepted for Publication in PASP, 7 pages, 1 figure and 1 tabl
A Calibration Method for Wide Field Multicolor Photometric System
The purpose of this paper is to present a method to self-calibrate the
spectral energy distribution (SED) of objects in a survey based on the fitting
of an SED library to the observed multi-color photometry. We adopt for
illustrative purposes the Vilnius (Strizyz and Sviderskiene 1972) and Gunn &
Stryker (1983) SED libraries. The self-calibration technique can improve the
quality of observations which are not taken under perfectly photometric
conditions. The more passbands used for the photometry, the better the results.
This technique has been applied to the BATC 15-passband CCD survey.Comment: LateX file, 1 PS file, submitted to PASP number 99-025 The English
has been improved and some mistakes have been correcte
Spectral Energy Distributions of M81 Globular Clusters in BATC Multicolor Survey
In this paper, we give the spectral energy distributions of 42 M81 globular
clusters in 13 intermediate-band filters from 4000 to 10000 A, using the CCD
images of M81 observed as part of the BATC multicolor survey of the Sky. The
BATC multicolor filter system is specifically designed to exclude most of the
bright and variable night-sky emission lines including the OH forest. Hence, it
can present accurate SEDs of the observed objects. These spectral energy
distributions are low-resolution spectra, and can reflect the stellar
populations of the globular clusters. This paper confirms the conclusions of
Schroder et al. that, M81 contains clusters as young as a few Gyrs, which also
were observed in both M31 and M33Comment: Accepted for Publication in PASP, 10 pages, 3 figure
Research on Precipitation Prediction Model Based on Extreme Learning Machine Ensemble
Precipitation is a significant index to measure the degree of drought and flood in a region, which directly reflects the local natural changes and ecological environment. It is very important to grasp the change characteristics and law of precipitation accurately for effectively reducing disaster loss and maintaining the stable development of a social economy. In order to accurately predict precipitation, a new precipitation prediction model based on extreme learning machine ensemble (ELME) is proposed. The integrated model is based on the extreme learning machine (ELM) with different kernel functions and supporting parameters, and the submodel with the minimum root mean square error (RMSE) is found to fit the test data. Due to the complex mechanism and factors affecting precipitation change, the data have strong uncertainty and significant nonlinear variation characteristics. The mean generating function (MGF) is used to generate the continuation factor matrix, and the principal component analysis technique is employed to reduce the dimension of the continuation matrix, and the effective data features are extracted. Finally, the ELME prediction model is established by using the precipitation data of Liuzhou city from 1951 to 2021 in June, July and August, and a comparative experiment is carried out by using ELM, long-term and short-term memory neural network (LSTM) and back propagation neural network based on genetic algorithm (GA-BP). The experimental results show that the prediction accuracy of the proposed method is significantly higher than that of other models, and it has high stability and reliability, which provides a reliable method for precipitation prediction
Parallel Implementation of Katsevich's FBP Algorithm
For spiral cone-beam CT, parallel computing is an effective
approach to resolving the problem of heavy computation burden. It
is well known that the major computation time is spent in the
backprojection step for either filtered-backprojection (FBP) or
backprojected-filtration (BPF) algorithms. By the cone-beam cover
method [1], the backprojection procedure is driven by cone-beam
projections, and every cone-beam projection can be backprojected
independently. Basing on this fact, we develop a parallel
implementation of Katsevich's FBP algorithm. We do all the
numerical experiments on a Linux cluster. In one typical
experiment, the sequential reconstruction time is 781.3 seconds,
while the parallel reconstruction time is 25.7 seconds with 32
processors
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