276 research outputs found
High resolution numerical-relativity simulations for the merger of binary magnetized neutron stars
We perform high-resolution magnetohydrodynamics simulations of binary neutron
star mergers in numerical relativity on the Japanese supercomputer K. The
neutron stars and merger remnants are covered by a grid spacing of 70\,m, which
yields the highest-resolution results among those derived so far. By an
in-depth resolution study, we clarify several amplification mechanisms of
magnetic fields during the binary neutron star merger for the first time.
First, the Kelvin-Helmholtz instability developed in the shear layer at the
onset of the merger significantly amplifies the magnetic fields. A hypermassive
neutron star (HMNS) formed after the merger is then subject to the
nonaxisymmetric magnetorotational instability, which amplifies the magnetic
field in the HMNS. These two amplification mechanisms cannot be found with
insufficient-resolution runs. We also show that the HMNS eventually collapses
to a black hole surrounded by an accretion torus which is strongly magnetized
at birth.Comment: 5 pages, 4 figures, to be appeared in PRD rapid communicatio
High-resolution magnetohydrodynamics simulation of black hole-neutron star merger: Mass ejection and short gamma-ray burst
We report results of a high-resolution numerical-relativity simulation for
the merger of black hole-magnetized neutron star binaries on Japanese
supercomputer "K". We focus on a binary that is subject to tidal disruption and
subsequent formation of a massive accretion torus. We find the launch of
thermally driven torus wind, subsequent formation of a funnel wall above the
torus and a magnetosphere with collimated poloidal magnetic field, and high
Blandford-Znajek luminosity. We show for the first time this picture in a
self-consistent simulation. The turbulence-like motion induced by the
non-axisymmetric magnetorotational instability as well as the Kelvin-Helmholtz
instability inside the accretion torus works as an agent to drive the mass
accretion and converts the accretion energy to thermal energy, which results in
the generation of a strong wind. By an in-depth resolution study, we reveal
that high resolution is essential to draw such a picture. We also discuss the
implication for the r-process nucleosynthesis, the radioactively-powered
transient emission, and short gamma-ray bursts.Comment: 8 pages, 8 figures, to be appeared in PR
Effect of Suplatast Tosilate on Antileukotriene Non-Responders with Mild-to-Moderate Persistent Asthma
ABSTRACTBackgroundImmunomodulatory therapy has been recently introduced for the management of asthma. Suplatast tosilate (ST), a new immune-modifying drug, is known to improve the airway function by inhibiting the release of Th-2 cytokines. However, its efficacy as a controller listed in the guideline, Global Initiative for Asthma 2005 has not been established. In this study we investigated the role of ST in leukotriene receptor antagonist (LTRA) non-responders with mild-to-moderate persistent asthma before initiating corticosteroids inhalation therapy.MethodsThis was a prospective open-level clinical trial. LTRAs was given to 41 patients with asthma for 4 weeks and clinical efficacy was assessed using daily symptom scores. The 10 patients, aged 2.5-8.5 years, who failed to show clinical improvement, were defined as LTRA non-responders. After a 1-week washout period, the efficacy of ST was investigated and compared with LTRA non-responders for the following 4 weeks.ResultsLTRA non-responders showed a significant improvement in the average symptom score, peak expiratory flow, use of rescue medication and the proportion of symptom-free days with ST therapy.ConclusionsST is a good choice for patients who have failed to respond to LTRAs. ST should therefore be added to the list of treatment options for such patients
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
Growing Neural Gas with Different Topologies for 3D Space Perception
Three-dimensional space perception is one of the most important capabilities for an autonomous mobile robot in order to operate a task in an unknown environment adaptively since the autonomous robot needs to detect the target object and estimate the 3D pose of the target object for performing given tasks efficiently. After the 3D point cloud is measured by an RGB-D camera, the autonomous robot needs to reconstruct a structure from the 3D point cloud with color information according to the given tasks since the point cloud is unstructured data. For reconstructing the unstructured point cloud, growing neural gas (GNG) based methods have been utilized in many research studies since GNG can learn the data distribution of the point cloud appropriately. However, the conventional GNG based methods have unsolved problems about the scalability and multi-viewpoint clustering. In this paper, therefore, we propose growing neural gas with different topologies (GNG-DT) as a new topological structure learning method for solving the problems. GNG-DT has multiple topologies of each property, while the conventional GNG method has a single topology of the input vector. In addition, the distance measurement in the winner node selection uses only the position information for preserving the environmental space of the point cloud. Next, we show several experimental results of the proposed method using simulation and RGB-D datasets measured by Kinect. In these experiments, we verified that our proposed method almost outperforms the other methods from the viewpoint of the quantization and clustering errors. Finally, we summarize our proposed method and discuss the future direction on this research
Learning Domain Invariant Representations by Joint Wasserstein Distance Minimization
Domain shifts in the training data are common in practical applications of
machine learning, they occur for instance when the data is coming from
different sources. Ideally, a ML model should work well independently of these
shifts, for example, by learning a domain-invariant representation. Moreover,
privacy concerns regarding the source also require a domain-invariant
representation. In this work, we provide theoretical results that link domain
invariant representations -- measured by the Wasserstein distance on the joint
distributions -- to a practical semi-supervised learning objective based on a
cross-entropy classifier and a novel domain critic. Quantitative experiments
demonstrate that the proposed approach is indeed able to practically learn such
an invariant representation (between two domains), and the latter also supports
models with higher predictive accuracy on both domains, comparing favorably to
existing techniques.Comment: 20 pages including appendix. Under Revie
マウスガードの自律神経活動への影響 : 瞳孔フラッシュ応答による定量的評価
Background:Recently, it has been reported that mouth guards (MGs), which reduce the incidence and severity of traumatic oral injuries in contact sports, may actually affect sports performance. We have observed that a majority of subjects showed improved dynamic visual acuity during head rotation when using a MG, but subjects who were unwilling to use a MG showed the opposite effect. Thus, we hypothesized that unpleasant sensations due to MGs may decrease sports performance.Methods:In this study, we measured autonomic nervous system activity to evaluate unpleasant sensations objectively and quantitatively by measuring the pupillary flash response (PFR) and heart rate variability (HRV), before, during, and after wearing 3- and 5-mm-thick custom-made MGs in 10 healthy subjects.Results:It was found that the 5-mm MG had a higher incidence of unpleasant sensations (50% of subjects) than did the 3-mm MG (10%). PFR (not HRV) analysis showed that both sympathetic and parasympathetic nervous system activities increased in subjects with unpleasant sensations.Conclusions:We suggest that the unpleasant sensation induced this unusual autonomic nervous system response, which could not be detected by traditional methods such as HRV analysis. By using PFR analysis, it is possible to make MGs without unpleasant sensations for better sports performance.博士(医学)・乙第1306号・平成24年11月27日Copyright © 2012 Japanese Stomatological Society. Published by Elsevier Japan K
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