240 research outputs found
Large eddy simulation of a turbulent flow in a 5 x 5 rod bundle with a mixing vane spacer grid
In fuel assemblies of pressurized water reactors (PWRs), mixing-vane spacer grids are extensively employed to array fuel rods and enhance inter- and intra-subchannel mixing. The turbulent flow downstream of spacer grids is essential knowledge to support the design of spacer grids and mixing vanes. As a high-fidelity approach for turbulence simulation, large eddy simulation (LES) results are assessed with the high-resolution flow field measured with particle image velocimetry (PIV). The LES results reveal a mixing vane effect on vortex structures and Reynolds stresses. The mechanism of vortex generation at the mixing vanes and the development downstream of the spacer grid are visualized by the Q-criterion. The distributions of the root mean square fluctuating velocity and Reynolds stresses decay rapidly downstream of the spacer grid. The secondary flow intensity downstream of the spacer grid predicted by LES is evaluated and follows an exponentially decaying law with distance from the spacer grid
Adversarial Attacks and Defenses for Semantic Communication in Vehicular Metaverses
For vehicular metaverses, one of the ultimate user-centric goals is to
optimize the immersive experience and Quality of Service (QoS) for users on
board. Semantic Communication (SemCom) has been introduced as a revolutionary
paradigm that significantly eases communication resource pressure for vehicular
metaverse applications to achieve this goal. SemCom enables high-quality and
ultra-efficient vehicular communication, even with explosively increasing data
traffic among vehicles. In this article, we propose a hierarchical
SemCom-enabled vehicular metaverses framework consisting of the global
metaverse, local metaverses, SemCom module, and resource pool. The global and
local metaverses are brand-new concepts from the metaverse's distribution
standpoint. Considering the QoS of users, this article explores the potential
security vulnerabilities of the proposed framework. To that purpose, this study
highlights a specific security risk to the framework's SemCom module and offers
a viable defense solution, so encouraging community researchers to focus more
on vehicular metaverse security. Finally, we provide an overview of the open
issues of secure SemCom in the vehicular metaverses, notably pointing out
potential future research directions
GDNF secreted from adipose-derived stem cells stimulates VEGF-independent angiogenesis
Adipose tissue stroma contains a population of mesenchymal stem cells (MSC) promote new blood vessel formation and stabilization. These adipose-derived stem cells (ASC) promote de novo formation of vascular structures in vitro. We investigated the angiogenic factors secreted by ASC and discovered that glial-derived neurotrophic factor (GDNF) is a key mediator for endothelial cell network formation. It was found that both GDNF alone or present in ASC-conditioned medium (ASC-CM) stimulated capillary network formation by using human umbilical vein endothelial cells (HUVECs) and such an effect was totally independent of vascular endothelial growth factor (VEGF) activity. Additionally, we showed stimulation of capillary network formation by GDNF, but not VEGF, could be blocked by the Ret (rearranged during transfection) receptor antagonist RPI-1, a GDNF signaling inhibitor. Furthermore, GDNF were found to be overexpressed in cancer cells that were resistant to the anti-angiogenic treatment using the VEGF antibody. Cancer cells in the liver hepatocellular carcinoma (HCC), a non-nervous related cancer, highly overexpressed GDNF as compared to normal liver cells. Our data strongly suggest that, in addition to VEGF, GDNF secreted by ASC and HCC cells, may be another important factor promoting pathological neovascularization. Thus, GDNF may be a potential therapeutic target for HCC and obesity treatments
Abnormal expression of an ADAR2 alternative splicing variant in gliomas downregulates adenosine-to-inosine RNA editing
BACKGROUND: RNA editing is catalyzed by adenosine deaminases acting on RNA (ADARs). ADAR2 is the main enzyme responsible for recoding editing in humans. Adenosine-to-inosine (A-to-I) editing at the Q/R site is reported to be decreased in gliomas; however, the expression of ADAR2 mRNA was not greatly affected. METHODS: We determined ADAR2 mRNA expression in human glioblastoma cell lines and in normal human glial cells by real-time RT-PCR. We also determined ADAR2 mRNA expression in 44 glioma tissues and normal white matter. After identifying an alternative splicing variant (ASV) of ADAR2 in gliomas, we performed sequencing. We then classified glioblastomas based on the presence (+) or absence (–) of the ASV to determine the correlations between ASV + and malignant features of glioblastomas, such as invasion, peritumoral brain edema, and survival time. RESULTS: There were no significant differences in ADAR2 mRNA expression among human glioblastoma cell lines or in gliomas compared with normal white matter (all p > 0.05). The ASV, which contained a 47-nucleotide insertion in the ADAR2 mRNA transcript, was detected in the U251 and BT325 cell lines, and in some glioma tissues. The expression rate of ASV differed among gliomas of different grades. ASV + glioblastomas were more malignant than ASV – glioblastomas. CONCLUSIONS: ADAR2 is a family of enzymes in which ASVs result in differences in enzymatic activity. The ADAR2 ASV may be correlated with the invasiveness of gliomas. Identification of the mechanistic characterization of ADAR2 ASV may have future potential for individualized molecular targeted-therapy for glioma
Ions-induced Epitaxial Growth of Perovskite Nanocomposites for Highly Efficient Light-Emitting Diodes with EQE Exceeding 30%
Cesium lead bromide (CsPbBr3) is a widely used emitter for perovskite
light-emitting diodes (PeLEDs), benefiting from its large carrier mobility,
high color purity and good thermal stability. However, the three-dimensional
CsPbBr3 films encounter challenges due to their massive intrinsic defects and
weak exciton binding effect, which limited their electroluminescence
efficiency. To address this issue, the prevailing approach is to confine
carriers by reducing dimensionality or size. Nonetheless, this method results
in an increase in surface trap states due to the larger surface-to-volume ratio
and presents difficulties in carrier injection and transport after reducing
lattice splitting to smaller sizes. Here, we successfully achieved proper
control over film crystallization by introducing sodium ions, which facilitate
the epitaxial growth of zero-dimensional Cs4PbBr6 on the surface of CsPbBr3,
forming large grain matrixes where CsPbBr3 is encapsulated by Cs4PbBr6.
Notably, the ions-induced epitaxial growth enables the CsPbBr3 emitter with
significantly reduced trap states, and generates coarsened nanocomposites of
CsPbBr3&Cs4PbBr6 with grain size that surpass the average thickness of the thin
perovskite film, resulting in a wavy surface conducive to light out-coupling.
Additionally, another additive of formamidinium chloride was incorporated to
assist the growth of nanocomposites with larger size and lower defects as well
as better carrier injection and transportation. As a result, our demonstrated
PeLEDs based on the coarsened nanocomposites exhibit low nonradiative
recombination, enhanced light extraction and well-balanced carrier
transportation, leading to high-performance devices. The champion device
achieved an external quantum efficiency of 31.0% at the emission peak of 521 nm
with a narrow full width at half-maximum (FWHM) of 18 nm
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