417 research outputs found
A Linear Programming Approach for Molecular QSAR analysis
Small molecules in chemistry can be represented as graphs. In a quantitative structure-activity relationship (QSAR) analysis, the central task is to find a regression function that predicts the activity of the molecule in high accuracy. Setting a QSAR as a primal target, we propose a new linear programming approach to the graph-based regression problem. Our method extends the graph classification algorithm by Kudo et al. (NIPS 2004), which is a combination of boosting and graph mining. Instead of sequential multiplicative updates, we employ the linear programming boosting (LP) for regression. The LP approach allows to include inequality constraints for the parameter vector, which turns out to be particularly useful in QSAR tasks where activity values are sometimes unavailable. Furthermore, the efficiency is improved significantly by employing multiple pricing
Rotationally-Driven Fragmentation for the Formation of the Binary Protostellar System L1551 IRS 5
Either bulk rotation or local turbulence is widely invoked to drive
fragmentation in collapsing cores so as to produce multiple star systems. Even
when the two mechanisms predict different manners in which the stellar spins
and orbits are aligned, subsequent internal or external interactions can drive
multiple systems towards or away from alignment thus masking their formation
process. Here, we demonstrate that the geometrical and dynamical relationship
between the binary system and its surrounding bulk envelope provide the crucial
distinction between fragmentation models. We find that the circumstellar disks
of the binary protostellar system L1551 IRS 5 are closely parallel not just
with each other but also with their surrounding flattened envelope.
Measurements of the relative proper motion of the binary components spanning
nearly 30 yr indicate an orbital motion in the same sense as the envelope
rotation. Eliminating orbital solutions whereby the circumstellar disks would
be tidally truncated to sizes smaller than are observed, the remaining
solutions favor a circular or low-eccentricity orbit tilted by up to
25 from the circumstellar disks. Turbulence-driven fragmentation
can generate local angular momentum to produce a coplanar binary system, but
which bears no particular relationship with its surrounding envelope. Instead,
the observed properties conform with predictions for rotationally-driven
fragmentation. If the fragments were produced at different heights or on
opposite sides of the midplane in the flattened central region of a rotating
core, the resulting protostars would then exhibit circumstellar disks parallel
with the surrounding envelope but tilted from the orbital plane as is observed.Comment: Accepted for publication in Ap
Space-efficient Feature Maps for String Alignment Kernels
String kernels are attractive data analysis tools for analyzing string data.
Among them, alignment kernels are known for their high prediction accuracies in
string classifications when tested in combination with SVM in various
applications. However, alignment kernels have a crucial drawback in that they
scale poorly due to their quadratic computation complexity in the number of
input strings, which limits large-scale applications in practice. We address
this need by presenting the first approximation for string alignment kernels,
which we call space-efficient feature maps for edit distance with moves
(SFMEDM), by leveraging a metric embedding named edit sensitive parsing (ESP)
and feature maps (FMs) of random Fourier features (RFFs) for large-scale string
analyses. The original FMs for RFFs consume a huge amount of memory
proportional to the dimension d of input vectors and the dimension D of output
vectors, which prohibits its large-scale applications. We present novel
space-efficient feature maps (SFMs) of RFFs for a space reduction from O(dD) of
the original FMs to O(d) of SFMs with a theoretical guarantee with respect to
concentration bounds. We experimentally test SFMEDM on its ability to learn SVM
for large-scale string classifications with various massive string data, and we
demonstrate the superior performance of SFMEDM with respect to prediction
accuracy, scalability and computation efficiency.Comment: Full version for ICDM'19 pape
More supplements to a class of logarithmically completely monotonic functions associated with the gamma function
In this article, a necessary and sufficient condition and a necessary
condition are established for a function involving the gamma function to be
logarithmically completely monotonic on . As applications of the
necessary and sufficient condition, some inequalities for bounding the psi and
polygamma functions and the ratio of two gamma functions are derived.Comment: 8 page
Protostellar collapse: rotation and disk formation
We present some important conclusions from recent calculations pertaining to
the collapse of rotating molecular cloud cores with axial symmetry,
corresponding to evolution of young stellar objects through classes 0 and begin
of class I. Three main issues have been addressed: (1) The typical timescale
for building up a preplanetary disk - once more it turned out that it is of the
order of one free-fall time which is decisively shorter than the widely assumed
timescale related to the so-called 'inside-out collapse'; (2) Redistribution of
angular momentum and the accompanying dissipation of kinetic (rotational)
energy - together these processes govern the mechanical and thermal evolution
of the protostellar core to a large extent; (3) The origin of
calcium-aluminium-rich inclusions (CAIs) - due to the specific pattern of the
accretion flow, material that has undergone substantial chemical and
mineralogical modifications in the hot (exceeding 900 K) interior of the
protostellar core may have a good chance to be advectively transported outward
into the cooler remote parts (beyond 4 AU, say) of the growing disk and to
survive there until it is incorporated into a meteoritic body.Comment: 4 pages, 4 figure
Kinematic Structure of Molecular Gas around High-mass Star YSO, Papillon Nebula, in N159 East in the Large Magellanic Cloud
We present the ALMA Band 3 and Band 6 results of 12CO(2-1), 13$CO(2-1),
H30alpha recombination line, free-free emission around 98 GHz, and the dust
thermal emission around 230 GHz toward the N159 East Giant Molecular Cloud
(N159E) in the Large Magellanic Cloud (LMC). LMC is the nearest active
high-mass star forming face-on galaxy at a distance of 50 kpc and is the best
target for studing high-mass star formation. ALMA observations show that N159E
is the complex of filamentary clouds with the width and length of ~1 pc and 5
pc - 10 pc, respectively. The total molecular mass is 0.92 x 10^5 Msun from the
13CO(2-1) intensity. N159E harbors the well-known Papillon Nebula, a compact
high-excitation HII region. We found that a YSO associated with the Papillon
Nebula has the mass of 35 Msun and is located at the intersection of three
filamentary clouds. It indicates that the formation of the high-mass YSO was
induced by the collision of filamentary clouds. Fukui et al. 2015 reported a
similar kinematic structure toward a YSO in the N159 West region which is
another YSO that has the mass larger than 35 Msun in these two regions. This
suggests that the collision of filamentary clouds is a primary mechanism of
high-mass star formation. We found a small molecular hole around the YSO in
Papillon Nebula with sub-pc scale. It is filled by free-free and H30alpha
emission. Temperature of the molecular gas around the hole reaches ~ 80 K. It
indicates that this YSO has just started the distruction of parental molecular
cloud.Comment: 28 pages, 7 figures. Submitted to Ap
Probabilistic Clustering of Time-Evolving Distance Data
We present a novel probabilistic clustering model for objects that are
represented via pairwise distances and observed at different time points. The
proposed method utilizes the information given by adjacent time points to find
the underlying cluster structure and obtain a smooth cluster evolution. This
approach allows the number of objects and clusters to differ at every time
point, and no identification on the identities of the objects is needed.
Further, the model does not require the number of clusters being specified in
advance -- they are instead determined automatically using a Dirichlet process
prior. We validate our model on synthetic data showing that the proposed method
is more accurate than state-of-the-art clustering methods. Finally, we use our
dynamic clustering model to analyze and illustrate the evolution of brain
cancer patients over time
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