22 research outputs found
A Study on Deep CNN Structures for Defect Detection From Laser Ultrasonic Visualization Testing Images
The importance of ultrasonic nondestructive testing has been increasing in
recent years, and there are high expectations for the potential of laser
ultrasonic visualization testing, which combines laser ultrasonic testing with
scattered wave visualization technology. Even if scattered waves are
visualized, inspectors still need to carefully inspect the images. To automate
this, this paper proposes a deep neural network for automatic defect detection
and localization in LUVT images. To explore the structure of a neural network
suitable to this task, we compared the LUVT image analysis problem with the
generic object detection problem. Numerical experiments using real-world data
from a SUS304 flat plate showed that the proposed method is more effective than
the general object detection model in terms of prediction performance. We also
show that the computational time required for prediction is faster than that of
the general object detection model
Simulation-Aided Deep Learning for Laser Ultrasonic Visualization Testing
In recent years, laser ultrasonic visualization testing (LUVT) has attracted
much attention because of its ability to efficiently perform non-contact
ultrasonic non-destructive testing.Despite many success reports of deep
learning based image analysis for widespread areas, attempts to apply deep
learning to defect detection in LUVT images face the difficulty of preparing a
large dataset of LUVT images that is too expensive to scale. To compensate for
the scarcity of such training data, we propose a data augmentation method that
generates artificial LUVT images by simulation and applies a style transfer to
simulated LUVT images.The experimental results showed that the effectiveness of
data augmentation based on the style-transformed simulated images improved the
prediction performance of defects, rather than directly using the raw simulated
images for data augmentation
Erythrocyte-Rich Thrombus Is Associated with Reduced Number of Maneuvers and Procedure Time in Patients with Acute Ischemic Stroke Undergoing Mechanical Thrombectomy
Background: Only few studies have investigated the relationship between the histopathology of retrieved thrombi and clinical outcomes. This study aimed to evaluate thrombus composition and its association with clinical, laboratory, and neurointerventional findings in patients treated by mechanical thrombectomy due to acute large vessel occlusion. Methods: At our institution, 79 patients were treated by mechanical thrombectomy using a stent retriever and/or aspiration catheter between August 2015 and August 2016. The retrieved thrombi were quantitatively analyzed to quantify red blood cells, white blood cells, and fibrin by area. We divided the patients into two groups – a fibrin-rich group and an erythrocyte-rich group – based on the predominant composition in the thrombus. The groups were compared for imaging, clinical, and neurointerventional data. Results: The retrieved thrombi from 43 patients with acute stroke from internal carotid artery, middle cerebral artery, or basilar artery occlusion were histologically analyzed. Erythrocyte-rich thrombi were present in 18 cases, while fibrin-rich thrombi were present in 25 cases. A cardioembolic etiology was significantly more prevalent among the patients with fibrin-rich thrombi than among those with erythrocyte-rich thrombi. Attenuation of thrombus density as shown on computed tomography images was greater in patients with erythrocyte-rich thrombi than in those with fibrin-rich thrombi. All other clinical and laboratory characteristics remained the same. Patients with erythrocyte-rich thrombi had a smaller number of recanalization maneuvers, shorter procedure times, a shorter time interval between arrival and recanalization, and a higher percentage of stent retrievers in the final recanalization procedure. The occluded vessels did not differ significantly. Conclusions: In this study, erythrocyte-rich thrombus was associated with noncardioembolic etiology, higher thrombus density, and reduced procedure time
Plasma Wakefield Acceleration Experiments in Overdense Regime Driven by Narrow Bunches
Experiments of plasma wakefield acceleration driven by narrow bunches were performed in overdense regime at the University of Tokyo. Changes of energy and beam size of test bunches caused by the driven bunches were observed. Acceleration gradient about 1 MeV/m was observed. Introduction Plasma wakefield acceleration is one of the methods which are proposed in order to obtain an acceleration gradient high enough for the next generation of linear colliders[1]. The concept has been first tested experimentally in 1988 at the Argonne National Laboratory[2]. More recently, gradient of 20 MeV/m has been produced by a train of bunches from the 500 MeV linac at KEK[3]. In this experiments, we have investigated dependence of acceleration characteristics on the plasma density in the overdense regime, in which plasma density is higher than the beam density. The drive beams were narrow; in other words, the product of plasma wavenumber and the beam size was less than unity. Changes in size and ener..