Dielectric energy storage capacitors have advantages such as ultra-high power density, extremely fast charge and discharge speed, long service lifespan and are significant for pulsed power system, ...smart power grid, and power electronics. Polypropylene (PP) is one of the most widely used dielectric materials for dielectric energy storage capacitors. It is of interest to investigate how to improve its electrical breakdown strength by nanodoping and the influencing mechanism of nanodoping on the electrical breakdown properties of polymer nanocomposites. PP/Al₂O₃ nanocomposite dielectric materials with various weight fraction of nanoparticles are fabricated by melt-blending and hot-pressing methods. Thermally stimulated current, surface potential decay, and dc electrical breakdown experiments show that deep trap properties and associated molecular chain motion are changed by incorporating nanofillers into polymer matrix, resulting in the variations in conductivity and dc electrical breakdown field of nanocomposite dielectrics. Then, a charge transport and molecular displacement modulated electrical breakdown model is utilized to simulate the dc electrical breakdown behavior. It is found that isolated interfacial regions formed in nanocomposite dielectrics at relatively low loadings reduce the effective carrier mobility and strengthen the interaction between molecular chains, hindering the transport of charges and the displacement of molecular chains with occupied deep traps. Accordingly, the electrical breakdown strength is enhanced at relatively low loadings. Interfacial regions may overlap in nanocomposite dielectrics at relatively high loadings so that the effective carrier mobility decreases and the interaction between molecular chains may be weakened. Consequently, the molecular motion is accelerated by electric force, leading to the decrease in electrical breakdown strength. The experiments and simulations reveals that the influence of nanodoping on dc electrical breakdown properties may origin from the changes in the charge transport and molecular displacement characteristics caused by interfacial regions in nanocomposite dielectrics.
Purpose:
This article presents a general procedural framework to assess the point-by-point precision in mapped dose associated with the intrinsic uncertainty of a deformable image registration (DIR) ...for any arbitrary patient.
Methods:
Dose uncertainty is obtained via a three-step process. In the first step, for each voxel in an imaging pair, a cluster of points is obtained by an iterative DIR procedure. In the second step, the dispersion of the points due to the imprecision of the DIR method is used to compute the spatial uncertainty. Two different ways to quantify the spatial uncertainty are presented in this work. Method A consists of a one-dimensional analysis of the modules of the position vectors, whereas method B performs a more detailed 3D analysis of the coordinates of the points. In the third step, the resulting spatial uncertainty estimates are used in combination with the mapped dose distribution to compute the point-by-point dose standard deviation. The process is demonstrated to estimate the dose uncertainty induced by mapping a 62.6 Gy dose delivered on maximum exhale to maximum inhale of a ten-phase four-dimensional lung CT.
Results:
For the demonstration lung image pair, the standard deviation of inconsistency vectors is found to be up to 9.2 mm with a mean
σ
of 1.3 mm. This uncertainty results in a maximum estimated dose uncertainty of 29.65 Gy if method A is used and 21.81 Gy for method B. The calculated volume with dose uncertainty above 10.00 Gy is
602
cm
3
for method A and
1422
cm
3
for method B.
Conclusions:
This procedure represents a useful tool to evaluate the precision of a mapped dose distribution due to the intrinsic DIR uncertainty in a patient. The procedure is flexible, allowing incorporation of alternative intrinsic error models.
Polypropylene (PP), with high breakdown strength, low dissipation and good processibility, is one of the most widely used dielectric material for power equipment, especially in power capacitors and ...power cables. The improvement of PP-based dielectric material can benefit the properties enhancement of power capacitors and cables, and thus to meet with the rapid development of the power system. Nanocomposite provided a promising orientation to reach the target and recent research approaches of PP nanocomposite for power equipment were reviewed in this paper. In this paper, we linked the nanofillers to the improved properties of PP nanocomposite, and categorised the research works into nanoclay/PP composites, metal oxide/PP nanocomposite, conductive particles/PP nanocomposite, and PP core–shell nanocomposites chronologically, corresponding to the enhanced thermal and mechanical property, breakdown strength property and energy storage property, respectively. Based on the achieved approaches, prospective for future research was proposed, providing a worth-considering direction for the future work.
•DIC is used to observe the deformation process of the PFRG.•Fiber factor is Introduced as an index to evaluate PE fiber.•Fiber factor increases, fracture toughness first increases and then ...decreases.•Fracture toughness calculation model of PFRG is established.
The influence of polyethylene fiber and water-binder ratio on the fracture properties of high toughness geopolymer is studied in this paper. Polyethylene fibers with 6 vol fractions (0, 0.25%, 0.45%, 0.65%, 0.85%, 1.05% and 1.25%) and different lengths (6 mm and 12 mm) were mixed into geopolymers having various water-binder ratios (0.35 and 0.38). A total of 26 experimental groups of polyethylene fiber reinforced geopolymer (PFRG) for notched beams were set up to observe the development process of displacement and deformation field during the three-point bending test by digital image correlation (DIC). The length, width, and height of the specimen were 160 mm, 40 mm, and 40 mm, respectively, with the initial crack length of 10 mm. The fracture test loading was displacement control, and the loading rate was 0.5 mm/min. The results indicated that the fiber factor (product of fiber length-diameter ratio and volume fraction) for PFRG can describe the comprehensive effect of fiber length and content. The literature shows that the fiber factor effectively improves the fracture performance of concrete materials, but the fracture toughness does not monotonously increase with the increase of the fiber factor. The fracture toughness of PFRG increased first and then decreased with the increase of fiber factor. The gain ratio of initial cracking toughness and unstable fracture toughness was reached to 4.395 and 6.332, respectively. Particularly, the optimum fiber factor can be set as 580.65. The fracture toughness of PFRG with a water-binder ratio of 0.35 was generally greater than that of 0.38. The gain ratio of unstable fracture toughness was greater than that of initial cracking toughness. This increased gain ratio indicates that the polyethylene fiber fully exerts its crack resistance effect only after the cracks appear in the specimen. By comparing the fracture toughness gain ratio of this paper with other literature, it is found that polyethylene fiber has a good toughening effect on geopolymer. Additionally, a fracture toughness prediction model was established via regression analysis, considering fiber factor and water-binder ratio as independent variables. The dense fiber factor Fd of polyethylene in this paper can be set as 600, which is higher than that of the other fibers due to its greater stiffness.
The performance of existing image-based training models in evaluating bowel preparation on colonoscopy videos was relatively low, and only a few models used external data to prove their ...generalization. Therefore, this study attempted to develop a more precise and stable AI system for assessing bowel preparation of colonoscopy video.
We proposed a system named ViENDO to assess the bowel preparation quality, including two CNNs. First, Information-Net was used to identify and filter out colonoscopy video frames unsuitable for Boston bowel preparation scale (BBPS) scoring. Second, BBPS-Net was trained and tested with 5,566 suitable short video clips through three-dimensional (3D) convolutional neural network (CNN) technology to detect BBPS-based insufficient bowel preparation. Then, ViENDO was applied to complete withdrawal colonoscopy videos from multiple centers to predict BBPS segment scores in clinical settings. We also conducted a human-machine contest to compare its performance with endoscopists.
In video clips, BBPS-Net for determining inadequate bowel preparation generated an area under the curve of up to 0.98 and accuracy of 95.2%. When applied to full-length withdrawal colonoscopy videos, ViENDO assessed bowel cleanliness with an accuracy of 93.8% in the internal test set and 91.7% in the external dataset. The human-machine contest demonstrated that the accuracy of ViENDO was slightly superior compared to most endoscopists, though no statistical significance was found.
The 3D-CNN-based AI model showed good performance in evaluating full-length bowel preparation on colonoscopy video. It has the potential as a substitute for endoscopists to provide BBPS-based assessments during daily clinical practice.
Protection from hardware attacks such as snoopers and mod chips has been receiving increasing attention in computer architecture. This paper presents a new combined memory encryption/authentication ...scheme. Our new split counters for counter-mode encryption simultaneously eliminate counter overflow problems and reduce per-block counter size, and we also dramatically improve authentication performance and security by using the Galois/Counter Mode of operation (GCM), which leverages counter-mode encryption to reduce authentication latency and overlap it with memory accesses. Our results indicate that the split-counter scheme has a negligible overhead even with a small (32KB) counter cache and using only eight counter bits per data block. The combined encryption/authentication scheme has an IPC overhead of 5% on average across SPEC CPU 2000 benchmarks, which is a significant improvement over the 20% overhead of existing encryption/authentication schemes.
In this paper we study collective additive tree spanners for special families of graphs including planar graphs, graphs with bounded genus, graphs with bounded tree-width, graphs with bounded ...clique-width, and graphs with bounded chordality. We say that a graph
G
=(
V
,
E
)
admits a system of
μ
collective additive tree
r
-spanners
if there is a system
of at most
μ
spanning trees of
G
such that for any two vertices
x
,
y
of
G
a spanning tree
exists such that
d
T
(
x
,
y
)≤
d
G
(
x
,
y
)+
r
. We describe a general method for constructing a “small” system of collective additive tree
r
-spanners with small values of
r
for “well” decomposable graphs, and as a byproduct show (among other results) that any weighted planar graph admits a system of
collective additive tree 0-spanners, any weighted graph with tree-width at most
k
−1 admits a system of
k
log
2
n
collective additive tree 0-spanners, any weighted graph with clique-width at most
k
admits a system of
k
log
3/2
n
collective additive tree
-spanners, and any weighted graph with size of largest induced cycle at most
c
admits a system of log
2
n
collective additive tree
-spanners and a system of 4log
2
n
collective additive tree
-spanners (here,
is the maximum edge weight in
G
). The latter result is refined for weighted weakly chordal graphs: any such graph admits a system of 4log
2
n
collective additive tree
-spanners. Furthermore, based on this collection of trees, we derive a compact and efficient routing scheme for those families of graphs.
Display omitted
•A nickel phosphate modified silicon nanowires arrays were obtained.•The nickel phosphate modified silicon nanowires showed good photoelectrochemical performance.•The nickel phosphate ...modified silicon nanowires could fasten the charge transfer.
Solar-driven photoelectrochemical (PEC) hydrogen production is a promising and environmentally friendly approach to relieve energy crisis and serve the carbon neutrality goal. Silicon nanowires (SiNWs), as one of p-type semiconductors, have more negative conduction band position than the water-resolved hydrogen potential, and wide range of light absorption due to their narrow band gap. Their PEC performance can be further improved by co-catalysts, and they can be used as photocathodes for hydrogen production. In this work, nickel phosphate (Ni3(PO4)2) was in situ decorated onto the SiNWs via a chemical vapor deposition (CVD). The Ni3(PO4)2 nanoparticles with diameters of about 20 to 50 nm were uniformly distributed on SiNWs arrays to construct heterostructures (Ni3(PO4)2-SiNWs). The Ni3(PO4)2-SiNWs composite showed a low onset potential to trigger water reduction. Compared with SiNWs, the Ni3(PO4)2-SiNWs composite had a much higher photocurrent and better PEC hydrogen production performance, which exhibited a stable photocurrent density of 16 mA cm−2 at 0 V (vs. reversible hydrogen electrode (RHE)) under simulated amplitude modulation (AM) 1.5G solar irradiation. This work provided a new solution to obtain nickel phosphate and fabricate the SiNWs-based photocathode.
•Cognitive load and storage interference are independently manipulated.•Recall performance is impaired by interference from a processing task.•Attention cannot help to reduce the interference induced ...performance impairment.
In the present study, we examined the hypothesis that the storage interference in working memory can be removed by attention. A dual-task paradigm was employed in Experiment 1 and 2, in which participants performed a color memory task and an RSVP letter detection task concurrently. The cognitive load of the RSVP letter detection task and the storage interference caused by the RSVP letter detection task was manipulated independently. That is, the produced storage-interference difference between the low and high interference conditions was comparable between the low and high cognitive load conditions, whereas the available attentional resources were different under the two cognitive load conditions. Since there were more attentional resources in the low load condition, the removal hypothesis predicts that differences in recall performance between the low and high interference conditions should be larger in high load than in low load, i.e., there would be an interaction between load and interference. However, the results of the two experiments did not show such an interaction. In Experiment 3, we manipulated the time available for the removal mechanism to work while inducing both the storage interference and processing interference. The results showed no sign of interference removal. Thus, the present results provided solid evidence to challenge the removal hypothesis.
Purpose:
To optimize modeling of interfractional anatomical variation during active breath-hold radiotherapy in lung cancer using principal component analysis (PCA).
Methods:
In 12 patients analyzed, ...weekly CT sessions consisting of three repeat intrafraction scans were acquired with active breathing control at the end of normal inspiration. The gross tumor volume (GTV) and lungs were delineated and reviewed on the first week image by physicians and propagated to all other images using deformable image registration. PCA was used to model the target and lung variability during treatment. Four PCA models were generated for each specific patient: (1) Individual models for the GTV and each lung from one image per week (week to week, W2W); (2) a W2W composite model of all structures; (3) individual models using all images (weekly plus repeat intrafraction images, allscans); and (4) composite model with all images. Models were reconstructed retrospectively (using all available images acquired) and prospectively (using only data acquired up to a time point during treatment). Dominant modes representing at least 95% of the total variability were used to reconstruct the observed anatomy. Residual reconstruction error between the model-reconstructed and observed anatomy was calculated to compare the accuracy of the models.
Results:
An average of 3.4 and 4.9 modes was required for the allscans models, for the GTV and composite models, respectively. The W2W model required one less mode in 40% of the patients. For the retrospective composite W2W model, the average reconstruction error was
0.7
±
0.2
mm
, which increased to
1.1
±
0.5
mm
when the allscans model was used. Individual and composite models did not have significantly different errors (
p
=
0.15
, paired
t
-test). The average reconstruction error for the prospective models of the GTV stabilized after four measurements at
1.2
±
0.5
mm
and for the composite model after five measurements at
0.8
±
0.4
mm
.
Conclusions:
Retrospective PCA models were capable of reconstructing original GTV and lung shapes and positions within several millimeters with three to four dominant modes, on average. Prospective models achieved similar accuracy after four to five measurements.
PDF
