150 research outputs found
Consistency of Oblique Decision Tree and its Boosting and Random Forest
Classification and Regression Tree (CART), Random Forest (RF) and Gradient
Boosting Tree (GBT) are probably the most popular set of statistical learning
methods. However, their statistical consistency can only be proved under very
restrictive assumptions on the underlying regression function. As an extension
to standard CART, the oblique decision tree (ODT), which uses linear
combinations of predictors as partitioning variables, has received much
attention. ODT tends to perform numerically better than CART and requires fewer
partitions. In this paper, we show that ODT is consistent for very general
regression functions as long as they are continuous. Then, we prove the
consistency of the ODT-based random forest (ODRF), whether fully grown or not.
Finally, we propose an ensemble of GBT for regression by borrowing the
technique of orthogonal matching pursuit and study its consistency under very
mild conditions on the tree structure. After refining existing computer
packages according to the established theory, extensive experiments on real
data sets show that both our ensemble boosting trees and ODRF have noticeable
overall improvements over RF and other forests
Direct observation of magnon-phonon coupling in yttrium iron garnet
The magnetic insulator yttrium iron garnet (YIG) with a ferrimagnetic
transition temperature of 560 K has been widely used in microwave and
spintronic devices. Anomalous features in the spin Seeback effect (SSE)
voltages have been observed in Pt/YIG and attributed to the magnon-phonon
coupling. Here we use inelastic neutron scattering to map out low-energy spin
waves and acoustic phonons of YIG at 100 K as a function of increasing magnetic
field. By comparing the zero and 9.1 T data, we find that instead of splitting
and opening up gaps at the spin wave and acoustic phonon dispersion
intersecting points, magnon-phonon coupling in YIG enhances the hybridized
scattering intensity. These results are different from expectations of
conventional spin-lattice coupling, calling for new paradigms to understand the
scattering process of magnon-phonon interactions and the resulting
magnon-polarons.Comment: 5 pages, 4 figures, PRB in pres
Topological triply-degenerate point with double Fermi arcs
Unconventional chiral particles have recently been predicted to appear in
certain three dimensional (3D) crystal structures containing three- or
more-fold linear band degeneracy points (BDPs). These BDPs carry topological
charges, but are distinct from the standard twofold Weyl points or fourfold
Dirac points, and cannot be described in terms of an emergent relativistic
field theory. Here, we report on the experimental observation of a topological
threefold BDP in a 3D phononic crystal. Using direct acoustic field mapping, we
demonstrate the existence of the threefold BDP in the bulk bandstructure, as
well as doubled Fermi arcs of surface states consistent with a topological
charge of 2. Another novel BDP, similar to a Dirac point but carrying nonzero
topological charge, is connected to the threefold BDP via the doubled Fermi
arcs. These findings pave the way to using these unconventional particles for
exploring new emergent physical phenomena
Familiarity-based Collaborative Team Recognition in Academic Social Networks
Collaborative teamwork is key to major scientific discoveries. However, the
prevalence of collaboration among researchers makes team recognition
increasingly challenging. Previous studies have demonstrated that people are
more likely to collaborate with individuals they are familiar with. In this
work, we employ the definition of familiarity and then propose MOTO
(faMiliarity-based cOllaborative Team recOgnition algorithm) to recognize
collaborative teams. MOTO calculates the shortest distance matrix within the
global collaboration network and the local density of each node. Central team
members are initially recognized based on local density. Then MOTO recognizes
the remaining team members by using the familiarity metric and shortest
distance matrix. Extensive experiments have been conducted upon a large-scale
data set. The experimental results show that compared with baseline methods,
MOTO can recognize the largest number of teams. The teams recognized by MOTO
possess more cohesive team structures and lower team communication costs
compared with other methods. MOTO utilizes familiarity in team recognition to
identify cohesive academic teams. The recognized teams are in line with
real-world collaborative teamwork patterns. Based on team recognition using
MOTO, the research team structure and performance are further analyzed for
given time periods. The number of teams that consist of members from different
institutions increases gradually. Such teams are found to perform better in
comparison with those whose members are from the same institution
Autonomous analysis of infrared images for condition diagnosis of HV cable accessories
Infrared thermography has been used as a key means for the identification of overheating defects in power cable accessories. At present, analysis of thermal imaging pictures relies on human visual inspections, which is time-consuming and laborious and requires engineering expertise. In order to realize intelligent, autonomous recognition of infrared images taken from electrical equipment, previous studies reported preliminary work in preprocessing of infrared images and in the extraction of key feature parameters, which were then used to train neural networks. However, the key features required manual selection, and previous reports showed no practical implementations. In this contribution, an autonomous diagnosis method, which is based on the Faster RCNN network and the Mean-Shift algorithm, is proposed. Firstly, the Faster RCNN network is trained to implement the autonomous identification and positioning of the objects to be diagnosed in the infrared images. Then, the Mean-Shift algorithm is used for image segmentation to extract the area of overheating. Next, the parameters determining the temperature of the overheating parts of cable accessories are calculated, based on which the diagnosis are then made by following the relevant cable condition assessment criteria. Case studies are carried out in the paper, and results show that the cable accessories and their overheating regions can be located and assessed at different camera angles and under various background conditions via the autonomous processing and diagnosis methods proposed in the paper
Learned Local Attention Maps for Synthesising Vessel Segmentations
Magnetic resonance angiography (MRA) is an imaging modality for visualising
blood vessels. It is useful for several diagnostic applications and for
assessing the risk of adverse events such as haemorrhagic stroke (resulting
from the rupture of aneurysms in blood vessels). However, MRAs are not acquired
routinely, hence, an approach to synthesise blood vessel segmentations from
more routinely acquired MR contrasts such as T1 and T2, would be useful. We
present an encoder-decoder model for synthesising segmentations of the main
cerebral arteries in the circle of Willis (CoW) from only T2 MRI. We propose a
two-phase multi-objective learning approach, which captures both global and
local features. It uses learned local attention maps generated by dilating the
segmentation labels, which forces the network to only extract information from
the T2 MRI relevant to synthesising the CoW. Our synthetic vessel segmentations
generated from only T2 MRI achieved a mean Dice score of in
testing, compared to state-of-the-art segmentation networks such as transformer
U-Net () and nnU-net(), while using only a
fraction of the parameters. The main qualitative difference between our
synthetic vessel segmentations and the comparative models was in the sharper
resolution of the CoW vessel segments, especially in the posterior circulation
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