200 research outputs found
Synthesis, Processing and Characterization of Polymer Derived Ceramic Nanocomposite Coating Reinforced with Carbon Nanotube Preforms
Ceramics have a number of applications as coating material due to their high hardness, wear and corrosion resistance, and the ability to withstand high temperatures. Critical to the success of these materials is the effective heat transfer through a material to allow for heat diffusion or effective cooling, which is often limited by the low thermal conductivity of many ceramic materials. To meet the challenge of improving the thermal conductivity of ceramics without lowering their performance envelope, carbon nanotubes were selected to improve the mechanical properties and thermal dispersion ability due to its excellent mechanical properties and high thermal conductivity in axial direction. However, the enhancements are far lower than expectation resulting from limited carbon nanotube content in ceramic matrix composites and the lack of alignment. These problems can be overcome if ceramic coatings are reinforced by carbon nanotubes with good dispersion and alignment. In this study, the well-dispersed and aligned carbon nanotubes preforms were achieved in the form of vertically aligned carbon nanotubes (VACNTs) and Buckypaper. Polymer derived ceramic (PDC) was selected as the matrix to fabricate carbon nanotube reinforced ceramic nanocomposites through resin curing and pyrolysis. The SEM images indicates the alignment of carbon nanotubes in the PDC nanocomposites. The mechanical and thermal properties of the PDC nanocomposites were characterized through Vickers hardness measurement and Thermogravimetric Analysis. The ideal anisotropic properties of nanocomposites were confirmed by estimating the electrical conductivity in two orthogonal directions
Advanced NOMA Assisted Semi-Grant-Free Transmission Schemes for Randomly Distributed Users
Non-orthogonal multiple access (NOMA) assisted semi-grant-free (SGF)
transmission has recently received significant research attention due to its
outstanding ability of serving grant-free (GF) users with grant-based (GB)
users' spectrum, {\color{blue}which can greatly improve the spectrum efficiency
and effectively relieve the massive access problem of 5G and beyond networks.
In this paper, we investigate the performance of SGF schemes under more
practical settings.} Firstly, we study the outage performance of the best user
scheduling SGF scheme (BU-SGF) by considering the impacts of Rayleigh fading,
path loss, and random user locations. Then, a fair SGF scheme is proposed by
applying cumulative distribution function (CDF)-based scheduling (CS-SGF),
which can also make full use of multi-user diversity. Moreover, by employing
the theories of order statistics and stochastic geometry, we analyze the outage
performances of both BU-SGF and CS-SGF schemes. Results show that full
diversity orders can be achieved only when the served users' data rate is
capped, which severely limit the rate performance of SGF schemes. To further
address this issue, we propose a distributed power control strategy to relax
such data rate constraint, and derive closed-form expressions of the two
schemes' outage performances under this strategy. Finally, simulation results
validate the fairness performance of the proposed CS-SGF scheme, the
effectiveness of the power control strategy, and the accuracy of the
theoretical analyses.Comment: 41 pages, 8 figure
Dynamic Resource Management in CDRT Systems through Adaptive NOMA
This paper introduces a novel adaptive transmission scheme to amplify the
prowess of coordinated direct and relay transmission (CDRT) systems rooted in
non-orthogonal multiple access principles. Leveraging the maximum ratio
transmission scheme, we seamlessly meet the prerequisites of CDRT while
harnessing the potential of dynamic power allocation and directional antennas
to elevate the system's operational efficiency. Through meticulous derivations,
we unveil closed-form expressions depicting the exact effective sum throughput.
Our simulation results adeptly validate the theoretical analysis and vividly
showcase the effectiveness of the proposed scheme.Comment: 11 pages, 7 figures, submitted to IEEE journal for revie
On Secure NOMA-Aided Semi-Grant-Free Systems
Semi-grant-free (SGF) transmission scheme enables grant-free (GF) users to
utilize resource blocks allocated for grant-based (GB) users while maintaining
the quality of service of GB users. This work investigates the secrecy
performance of non-orthogonal multiple access (NOMA)-aided SGF systems. First,
analytical expressions for the exact and asymptotic secrecy outage probability
(SOP) of NOMA-aided SGF systems with a single GF user are derived. Then, the
SGF systems with multiple GF users and a best-user scheduling scheme is
considered. By utilizing order statistics theory, closed-form expressions for
the exact and asymptotic SOP are derived. Monte Carlo simulation results
demonstrate the effects of system parameters on the SOP of the considered
system and verify the accuracy of the developed analytical results. The results
indicate that both the outage target rate for GB and the secure target rate for
GF are the main factors of the secrecy performance of SGF systems
LightBTSeg: A lightweight breast tumor segmentation model using ultrasound images via dual-path joint knowledge distillation
The accurate segmentation of breast tumors is an important prerequisite for
lesion detection, which has significant clinical value for breast tumor
research. The mainstream deep learning-based methods have achieved a
breakthrough. However, these high-performance segmentation methods are
formidable to implement in clinical scenarios since they always embrace high
computation complexity, massive parameters, slow inference speed, and huge
memory consumption. To tackle this problem, we propose LightBTSeg, a dual-path
joint knowledge distillation framework, for lightweight breast tumor
segmentation. Concretely, we design a double-teacher model to represent the
fine-grained feature of breast ultrasound according to different semantic
feature realignments of benign and malignant breast tumors. Specifically, we
leverage the bottleneck architecture to reconstruct the original Attention
U-Net. It is regarded as a lightweight student model named Simplified U-Net.
Then, the prior knowledge of benign and malignant categories is utilized to
design the teacher network combined dual-path joint knowledge distillation,
which distills the knowledge from cumbersome benign and malignant teachers to a
lightweight student model. Extensive experiments conducted on breast ultrasound
images (Dataset BUSI) and Breast Ultrasound Dataset B (Dataset B) datasets
demonstrate that LightBTSeg outperforms various counterparts.Comment: 7 pages, 7 figures, conferenc
Trajectory and power design for aerial CRNs with colluding eavesdroppers
Unmanned aerial vehicles (UAVs) can provide wireless access services to
terrestrial users without geographical limitations and will become an essential
part of the future communication system. However, the openness of wireless
channels and the mobility of UAVs make the security of UAV-based communication
systems particularly challenging. This work investigates the security of aerial
cognitive radio networks (CRNs) with multiple uncertainties colluding
eavesdroppers. A cognitive aerial base station transmits messages to cognitive
terrestrial users using the spectrum resource of the primary users. All
secondary terrestrial users and illegitimate receivers jointly decode the
received message. The average secrecy rate of the aerial CRNs is maximized by
jointly optimizing the UAV's trajectory and transmission power. An iterative
algorithm based on block coordinate descent and successive convex approximation
is proposed to solve the non-convex mixed-variable optimization problem.
Numerical results verify the effectiveness of our proposed algorithm and show
that our scheme improves the secrecy performance of airborne CRNs.Comment: 10 pages, 7 figures.submitted to the IEEE journal for revie
Different MRI-based radiomics models for differentiating misdiagnosed or ambiguous pleomorphic adenoma and Warthin tumor of the parotid gland: a multicenter study
PurposeTo evaluate the effectiveness of MRI-based radiomics models in distinguishing between Warthin tumors (WT) and misdiagnosed or ambiguous pleomorphic adenoma (PA).MethodsData of patients with PA and WT from two centers were collected. MR images were used to extract radiomic features. The optimal radiomics model was found by running nine machine learning algorithms after feature reduction and selection. To create a clinical model, univariate logistic regression (LR) analysis and multivariate LR were used. The independent clinical predictors and radiomics were combined to create a nomogram. Two integrated models were constructed by the ensemble and stacking algorithms respectively based on the clinical model and the optimal radiomics model. The models’ performance was evaluated using the area under the curve (AUC).ResultsThere were 149 patients included in all. Gender, age, and smoking of patients were independent clinical predictors. With the greatest average AUC (0.896) and accuracy (0.839) in validation groups, the LR model was the optimal radiomics model. In the average validation group, the radiomics model based on LR did not have a higher AUC (0.795) than the clinical model (AUC = 0.909). The nomogram (AUC = 0.953) outperformed the radiomics model in terms of discrimination performance. The nomogram in the average validation group had a highest AUC than the stacking model (0.914) or ensemble model (0.798).ConclusionMisdiagnosed or ambiguous PA and WT can be non-invasively distinguished using MRI-based radiomics models. The nomogram exhibited excellent and stable diagnostic performance. In daily work, it is necessary to combine with clinical parameters for distinguishing between PA and WT
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