709 research outputs found
A gauge-invariant and current-continuous microscopic ac quantum transport theory
There had been consensus on what the accurate ac quantum transport theory was
until some recent works challenged the conventional wisdom. Basing on the
non-equilibrium Green's function formalism for time-dependent quantum
transport, we derive an expression for the dynamic admittance that satisfies
gauge invariance and current continuity, and clarify the key concept in the
field. The validity of our now formalism is verified by first-principles
calculation of the transient current through a carbon-nanotube-based device
under the time-dependent bias voltage. Moreover, the previously well-accepted
expression for dynamic admittance is recovered only when the device is a
perfect conductor at a specific potential
The Eco-design and Green Manufacturing of a Refrigerator
AbstractThe paper introduces the Energy-related Products(ErP)directive and its late evolution. Both the general and the particular eco-design requirements of a refrigerator are presented. The criteria of standby/off are listed as well. The assumptions made for the modeling of the product and source of the database are put forward. There are 11 factors of environmental impacts used in the evaluation software EIME. The environmental impact of manufacturing, distribution, use and the end of life is analyzed according to a certain refrigerator. The results show that three factors are significant, which are electricity consumed by the refrigerator in the use stage, the raw materials of metal and plastics in the manufacturing. The solution to these problems is provided. The introduction of eco-design to development phase of a product is urgent nowadays
Improved Algebraic Algorithm On Point Projection For BĂ©zier Curves
International audienceThis paper presents an improved algebraic pruning method for point projection for BĂ©zier curves. It first turns the point projection into a root finding problem, and provides a simple but easily overlooked method to avoid finding invalid roots which is obviously irrelative to the closest point. The continued fraction method and its expansion are utilized to strengthen its robustness. Since NURBS curves can be easily turned into BĂ©zier form, the new method also works with NURBS curves. Examples are presented to illustrate the efficiency and robustness of the new method
HDR Video Reconstruction with a Large Dynamic Dataset in Raw and sRGB Domains
High dynamic range (HDR) video reconstruction is attracting more and more
attention due to the superior visual quality compared with those of low dynamic
range (LDR) videos. The availability of LDR-HDR training pairs is essential for
the HDR reconstruction quality. However, there are still no real LDR-HDR pairs
for dynamic scenes due to the difficulty in capturing LDR-HDR frames
simultaneously. In this work, we propose to utilize a staggered sensor to
capture two alternate exposure images simultaneously, which are then fused into
an HDR frame in both raw and sRGB domains. In this way, we build a large scale
LDR-HDR video dataset with 85 scenes and each scene contains 60 frames. Based
on this dataset, we further propose a Raw-HDRNet, which utilizes the raw LDR
frames as inputs. We propose a pyramid flow-guided deformation convolution to
align neighboring frames. Experimental results demonstrate that 1) the proposed
dataset can improve the HDR reconstruction performance on real scenes for three
benchmark networks; 2) Compared with sRGB inputs, utilizing raw inputs can
further improve the reconstruction quality and our proposed Raw-HDRNet is a
strong baseline for raw HDR reconstruction. Our dataset and code will be
released after the acceptance of this paper
Quantifying U-Net Uncertainty in Multi-Parametric MRI-based Glioma Segmentation by Spherical Image Projection
The projection of planar MRI data onto a spherical surface is equivalent to a
nonlinear image transformation that retains global anatomical information. By
incorporating this image transformation process in our proposed spherical
projection-based U-Net (SPU-Net) segmentation model design, multiple
independent segmentation predictions can be obtained from a single MRI. The
final segmentation is the average of all available results, and the variation
can be visualized as a pixel-wise uncertainty map. An uncertainty score was
introduced to evaluate and compare the performance of uncertainty measurements.
The proposed SPU-Net model was implemented on the basis of 369 glioma patients
with MP-MRI scans (T1, T1-Ce, T2, and FLAIR). Three SPU-Net models were trained
to segment enhancing tumor (ET), tumor core (TC), and whole tumor (WT),
respectively. The SPU-Net model was compared with (1) the classic U-Net model
with test-time augmentation (TTA) and (2) linear scaling-based U-Net (LSU-Net)
segmentation models in terms of both segmentation accuracy (Dice coefficient,
sensitivity, specificity, and accuracy) and segmentation uncertainty
(uncertainty map and uncertainty score). The developed SPU-Net model
successfully achieved low uncertainty for correct segmentation predictions
(e.g., tumor interior or healthy tissue interior) and high uncertainty for
incorrect results (e.g., tumor boundaries). This model could allow the
identification of missed tumor targets or segmentation errors in U-Net.
Quantitatively, the SPU-Net model achieved the highest uncertainty scores for
three segmentation targets (ET/TC/WT): 0.826/0.848/0.936, compared to
0.784/0.643/0.872 using the U-Net with TTA and 0.743/0.702/0.876 with the
LSU-Net (scaling factor = 2). The SPU-Net also achieved statistically
significantly higher Dice coefficients, underscoring the improved segmentation
accuracy.Comment: 31 pages, 9 figures, 1 tabl
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