Highlights
The crystalline Fe/MnO@C core–shell nanocapsules embedded in porous amorphous carbon matrix (FMCA) was prepared by a novel confinement strategy of modified arc-discharge method.
The ...heterogeneous crystalline–amorphous nanocrystals disperse evenly and exhibit improvement of static magnetization and excellent electromagnetic absorption properties.
The adding MnO
2
confines degree of graphitization and contributes to form amorphous carbon. Dielectric loss and microwave absorption are achieved adjustable.
Crystalline Fe/MnO@C core–shell nanocapsules inlaid in porous amorphous carbon matrix (FMCA) was synthesized successfully with a novel confinement strategy. The heterogeneous Fe/MnO nanocrystals are with approximate single-domain size which gives rise to natural resonance in 2–18 GHz. The addition of MnO
2
confines degree of graphitization catalyzed by iron and contributes to the formation of amorphous carbon. The heterogeneous materials composed of crystalline–amorphous structures disperse evenly and its density is significantly reduced on account of porous properties. Meanwhile, adjustable dielectric loss is achieved by interrupting Fe core aggregation and stacking graphene conductive network. The dielectric loss synergistically with magnetic loss endows the FMCA enhanced absorption. The optimal reflection loss (RL) is up to − 45 dB, and the effective bandwidth (RL < − 10 dB) is 5.0 GHz with 2.0 mm thickness. The proposed confinement strategy not only lays the foundation for designing high-performance microwave absorber, but also offers a general duty synthesis method for heterogeneous crystalline–amorphous composites with tunable composition in other fields.
The phase transition process of the MnO
2
phase with increases in Co
2+
doping can be described by the Ouroboros symbol. The undoped sample is pure δ-MnO
2
with nanosheets structures. Then a small ...amount of Co
2+
ions changes the final products and generates α-MnO
2
nanofibres in the δ-MnO
2
matrix. The products become pure α-MnO
2
with an appropriate amount of Co added. However, when the Co amount continues to increase, the amount of α-MnO
2
decreases in the products and turns back to form pure δ-MnO
2
in the end. Analysing the electromagnetic absorption performance, the relationship between the properties and the proportion of δ-MnO
2
/α-MnO
2
in the powders adjusted by Co
2+
doping has been explored, and the composites of δ-/α-MnO
2
show better absorption ability than the single-phase samples. As a result, the optimal reflection loss (RL) is −54.8 dB, and the effective absorption bandwidth can cover the Ku band at a thickness of 2.2 mm and the X band at a thickness of 3.1 mm with 50 wt.% filler loading ratios. This research might shed new light on the improvement of novel microwave absorption materials.
CircRNA
circ-PRDM5
(
PR/SET domain 5
) (circ-PRDM5) is overexpressed in age-related cataracts. Nevertheless, the biological role of circ-PRDM5 in posterior capsule opacities (PCO) (a common ...complication after cataract surgery) is unclear. Human lens epithelial cells SRA01/04 (LECs) were stimulated with TGF-β2 (transforming growth factor beta-2) to mimic the PCO model in vitro. Cell viability, migration, and invasion were determined by MTT, transwell, or wound-healing assays. Protein levels of EMT (epithelial-to-mesenchymal transition) markers and
COL1A2
(collagen type I alpha 2 chain) were analyzed by western blotting (WB). Relative expression of
circ-PRDM5
,
miR-92b-3p
, and
COL1A2
mRNA was analyzed by qRT-PCR. The targeting relationship was confirmed by dual-luciferase reporter and RIP assays. We observed that
circ-PRDM5
and
COL1A2
were upregulated in PCO tissues and TGF-β2-treated LECs, while
miR-92b-3p
was downregulated. Both
circ-PRDM5
and
COL1A2
knockdown impaired TGF-β2-induced LEC migration, invasion, and EMT. Also,
circ-PRDM5
could adsorb
miR-92b-3p
to regulate
COL1A2
expression. Furthermore,
miR-92b-3p
inhibitor offset
circ-PRDM5
knockdown-mediated influence on migration, invasion, and EMT of LECs under TGF-β2 stimulation. Also,
COL1A2
overexpression overturned the repressive influence of
miR-92b-3p
mimic on TGF-β2-induced LEC migration, invasion, and EMT. In summary, TGF-β2-induced circ-PRDM5 facilitated LEC migration, invasion, and EMT by adsorbing miR-92b-3p and increasing
COL1A2
expression, offering new insights into the development of PCO.
A 10-kV/400-V 500-kVA Electronic Power Transformer Wang, Dan; Tian, Jie; Mao, Chengxiong ...
IEEE transactions on industrial electronics (1982),
2016-Nov., 2016-11-00, 20161101, Letnik:
63, Številka:
11
Journal Article
Recenzirano
This paper presents the design and development of a three-phase 10-kV/400-V 500-kVA electronic power transformer (EPT). The power circuit is designed in a modular fashion, i.e., the main circuit ...consists of many identical ac-dc-dc-ac modules (abbreviated as power modules). Each power module consists of a high-voltage power cell, a low-voltage power cell (LVPC), a medium-frequency isolation transformer, and a filter. The corresponding control and protection system is developed. A special three-stage startup strategy is designed to shorten the startup time and reduce the startup inrush current. The negative-sequence current compensation is introduced in the input stage to handle the unbalanced loads. To keep the dc-link voltages balanced, an individual dc voltage balancing controller based on regulating the output power of each parallel LVPC is proposed. The detailed control hardware design and software implementation are discussed. The functions of this 10-kV EPT prototype are verified through the laboratory and field tests. The results are shown in this paper. Currently, the prototype is operating in the industrial power grid.
In view of the exceptional ability of curvature in connecting missing edges and structures, we propose novel sparse reconstruction models via the Euler’s elastica energy. In particular, we firstly ...extend the Euler’s elastica regularity into the nonlocal formulation to fully take the advantages of the pattern redundancy and structural similarity in image data. Due to its non-convexity, non-smoothness and nonlinearity, we regard both local and nonlocal elastica functional as the weighted total variation for a good trade-off between the runtime complexity and performance. The splitting techniques and alternating direction method of multipliers (ADMM) are used to achieve efficient algorithms, the convergence of which is also discussed under certain assumptions. The weighting function occurred in our model can be well estimated according to the local approach. Numerical experiments demonstrate that our nonlocal elastica model achieves the state-of-the-art reconstruction results for different sampling patterns and sampling ratios, especially when the sampling rate is extremely low.
Display omitted
•The prominent soft magnetic properties are ascribed to their special coherent microstructure.•A short-time ball-milling does not change the coherent BCC/ L21 structure of MEA ...powders.•The prominent soft magnetic and high resistivity, which contributes to the excellent electromagnetic wave-absorbing properties.•Al1.5Co3.5Fe3.5 flake powders possess the maximum effective bandwidth of 7.01 GHz with a sample thickness of 1.7 mm.
Magnetic alloy powders show a great superiority in the balance of permittivity and permeability for electromagnetic (EM) wave-absorption. However, it is necessary to enhance their effective absorption bandwidth (Δf) and impedance matching due to their insufficient soft-magnetic properties and low resistivity, which would be solved by high/medium-entropy alloys (HEAs/MEAs). In this report, we designed Al1.5Co3.5Fe3.5 and Al1.5Co3Fe3Cr MEAs with prominent soft-magnetic property and high resistivity. It is contributed to the special coherent microstructure with ultrafine magnetic body-centered-cubic nanoprecipitates uniformly-distributed into the L21 matrix, which could not be changed by ball-milling. Thus, alloy powders possess excellent EM properties, as evidenced by the minimum reflection loss of −42.2 dB at 14.52 GHz and the largest Δf = 7.01 GHz in 5 h-milled Al1.5Co3.5Fe3.5, better than existing alloy powders. The wave-absorbing behavior of MEA powders was discussed from both permittivity and permeability. The current findings offer a useful design strategy for developing high-performance absorbers.
The curvature regularities are well-known for providing strong priors in the continuity of edges, which have been applied to a wide range of applications in image processing and computer vision. ...However, these models are usually non-convex, non-smooth, and highly nonlinear, the first-order optimality condition of which are high-order partial differential equations. Thus, numerical computation is extremely challenging. In this paper, we estimate the discrete mean curvature and Gaussian curvature on the local
3
×
3
stencil, based on the fundamental forms in differential geometry. By minimizing certain functions of curvatures over the image surface, it yields a kind of weighted image surface minimization problem, which can be efficiently solved by the alternating direction method of multipliers. Numerical experiments on image restoration and inpainting are implemented to demonstrate the effectiveness and superiority of the proposed curvature-based model compared to state-of-the-art variational approches.
A 1.5 kV, 35 kW, 1 kHz silicon steel core medium-frequency transformer is designed and prototyped for a 10 kV, 0.5 MW electronic power transformer. This transformer uses 0.18 mm silicon steel as core ...material due to the advantages of easy processing, high saturation flux density, low noise, and low cost. The detailed design considerations and an optimal design method are presented in this paper. Different from the previous work on medium-frequency transformer design, the proposed approach takes ripples into account. Core loss model under square wave excitation with ripple and winding loss model considering sideband harmonics are established. Besides, two-dimensional finite-element simulations are adopted to obtain ac/dc resistance factors. Finally, the proposed approach is verified by experiments on prototype. The test results show performance better than expected, with desirable no-load loss and power density of 2.9623 × 10 6 W/m 3 .
Flaky carbonyl iron particles/nano silicon dioxide/Polyurethane (FCIP/SiO
2
/PU) composites coatings were fabricated. And FCIP were fabricated from sphere carbonyl iron particles (SCIP) by ball ...milling. The electromagnetic parameters of absorbers (SCIP, FCIP and SiO
2
) and the reflection loss (RL) of coatings were measured in the frequency range of 2–18 GHz. The results showed that the complex permeability and absorbing properties of FCIP are significantly enhanced compared with SCIP because of its smaller thickness and easy magnetization plane. In addition, as a low dielectric material, SiO
2
can build more wave-transmission channels and optimize the impedance matching, making more electromagnetic wave transmitting into the coatings and being attenuated. Due to the addition of SiO
2
, the absorbing properties and effective absorption bandwidth of coatings are further enhanced. The reflection loss values exceeding − 10 dB can be obtained in the frequency range of 8.5–18 GHz with a thickness of 1 mm.
Highlights
A multifunctional microwave modulator is developed for electromagnetic protection, infrared stealth and operating temperature monitoring over wide temperature ranges for the first time.
...Microwave modulator achieves the integration of two electromagnetic protection mechanisms, microwave absorption and radiation deflection.
Microwave modulator demonstrates the maximum effective bandwidth of 5.2 GHz with a thickness of only 1.5 mm in the temperature range 298–673 K.
High-temperature electromagnetic (EM) protection materials integrated of multiple EM protection mechanisms and functions are regarded as desirable candidates for solving EM interference over a wide temperature range. In this work, a novel microwave modulator is fabricated by introducing carbonyl iron particles (CIP)/resin into channels of carbonized wood (C-wood). Innovatively, the spaced arrangement of two microwave absorbents not only achieves a synergistic enhancement of magnetic and dielectric losses, but also breaks the translational invariance of EM characteristics in the horizontal direction to obtain multiple phase discontinuities in the frequency range of 8.2–18.0 GHz achieving modulation of reflected wave radiation direction. Accordingly, CIP/C-wood microwave modulator demonstrates the maximum effective bandwidth of 5.2 GHz and the maximum EM protection efficiency over 97% with a thickness of only 1.5 mm in the temperature range 298–673 K. Besides, CIP/C-wood microwave modulator shows stable and low thermal conductivities, as well as monotonic electrical conductivity-temperature characteristics, therefore it can also achieve thermal infrared stealth and working temperature monitoring in wide temperature ranges. This work provides an inspiration for the design of high-temperature EM protection materials with multiple EM protection mechanisms and functions.
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