221 research outputs found
VLBI Observations of Water Masers in Onsala 1: Massive Binary Star Forming Site?
We present proper motions of water masers toward the Onsala 1 star forming
region, observed with the Japanese VLBI network at three epochs spanning 290
days. We found that there are two water maser clusters (WMC1 and WMC2)
separated from each other by 1".6 (2900 AU at a distance of 1.8 kpc). The
proper motion measurement reveals that WMC1 is associated with a bipolar
outflow elongated in the east-west direction with an expansion velocity of
69+-11 km/s. WMC1 and WMC2 are associated with two 345 GHz continuum dust
emission sources, and located 2" (3600 AU) east from the core of an
ultracompact HII region traced by 8.4 GHz radio continuum emission. This
indicates that star formation activity of Onsala 1 could move from the west
side of ultracompact HII region to the east side of two young stellar objects
associated with the water masers. We also find that WMC1 and UC HII region
could be gravitationally bound. Their relative velocity along the line of sight
is 3 km/s, and total mass is 37 Mo. Onsala 1 seems to harbor a binary star at
different evolutionary stage.Comment: 9 pages, 4 figures, accepted for PAS
Towards Understanding the Mechanism of Contrastive Learning via Similarity Structure: A Theoretical Analysis
Contrastive learning is an efficient approach to self-supervised
representation learning. Although recent studies have made progress in the
theoretical understanding of contrastive learning, the investigation of how to
characterize the clusters of the learned representations is still limited. In
this paper, we aim to elucidate the characterization from theoretical
perspectives. To this end, we consider a kernel-based contrastive learning
framework termed Kernel Contrastive Learning (KCL), where kernel functions play
an important role when applying our theoretical results to other frameworks. We
introduce a formulation of the similarity structure of learned representations
by utilizing a statistical dependency viewpoint. We investigate the theoretical
properties of the kernel-based contrastive loss via this formulation. We first
prove that the formulation characterizes the structure of representations
learned with the kernel-based contrastive learning framework. We show a new
upper bound of the classification error of a downstream task, which explains
that our theory is consistent with the empirical success of contrastive
learning. We also establish a generalization error bound of KCL. Finally, we
show a guarantee for the generalization ability of KCL to the downstream
classification task via a surrogate bound
Efficient Model Selection for Predictive Pattern Mining Model by Safe Pattern Pruning
Predictive pattern mining is an approach used to construct prediction models
when the input is represented by structured data, such as sets, graphs, and
sequences. The main idea behind predictive pattern mining is to build a
prediction model by considering substructures, such as subsets, subgraphs, and
subsequences (referred to as patterns), present in the structured data as
features of the model. The primary challenge in predictive pattern mining lies
in the exponential growth of the number of patterns with the complexity of the
structured data. In this study, we propose the Safe Pattern Pruning (SPP)
method to address the explosion of pattern numbers in predictive pattern
mining. We also discuss how it can be effectively employed throughout the
entire model building process in practical data analysis. To demonstrate the
effectiveness of the proposed method, we conduct numerical experiments on
regression and classification problems involving sets, graphs, and sequences
Pilot VLBI Survey of SiO v=3 J=1--0 Maser Emission around Evolved Stars
In this Letter, we report detections of SiO v=3 J=1--0 maser emission in very
long baseline interferometric (VLBI) observations towards 4 out of 12
long-period variable stars: WX Psc, R Leo, W Hya, and T Cep. The detections
towards WX Psc and T Cep are new ones. We also present successful astrometric
observations of SiO v=2 and v=3 J=1--0 maser emissions associated with two
stars: WX Psc and W Hya and their position-reference continuum sources:
J010746.0+131205 and J135146.8-291218 with the VLBI Exploration of Radio
Astrometry (VERA). The relative coordinates of the position-reference continuum
source and SiO v=3 maser spots were measured with respect to those of an SiO
v=2 maser spot adopted as fringe-phase reference. Thus the faint continuum
sources were inversely phase-referenced to the bright maser sources. It implies
possible registration of multiple SiO maser line maps onto a common coordinate
system with 10 microarcsecond-level accuracy.Comment: 5 Pages, 3 figures, Fig.3 and Tab. 2 were corrected; Publications of
the Astronomical Society of Japan, Vol. 64, No. 6 issued on 2012 December 2
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