Significantly Enhanced Breakdown Strength and Energy Density in Nanocomposites by Synergic Modulation of Structural Design and Low-Loading Nanofibers.

Polymer-based dielectric nanocomposites have attracted great attention due to the advantages of high-power density and stability. However, due to the limited breakdown strength (Eb) of the dielectrics, the unsatisfactory energy density becomes the bottleneck that restricts their applications. Here, newly designed sandwich-structured nanocomposites are proposed, which includes the introduction of low-loading 0.4BiFeO3-0.6SrTiO3 (BFSTO) nanofibers into the poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) matrix as the polarization layer (B-layer) to offer high permittivity and the selection of poly(methylmethacrylate) (PMMA)/P(VDF-HFP) all-organic blend film as the insulation layer (P-layer) to improve Eb of the nanocomposites. The optimized sandwich-structured PBP nanocomposite exhibits significant enhancement in Eb (668.6 MV/m), generating a discharged energy density of 17.2 J/cm3. The dielectric and Kelvin probe force microscope results corroborate that the outer P-layer has a low surface charge density, which can markedly impede the charge injection from the electrode/dielectric interface and thereby suppress the leakage current inside the nanocomposite. Furthermore, both the finite element simulations and capacitive series models demonstrate that the homogenized distribution of electric field in the PBP sandwich-structured nanocomposite favors the improvement of energy storage performance. This work not only provides insightful guidance into the in-depth understanding of the dielectric breakdown mechanism in sandwich-structured nanocomposites but also offers a novel paradigm for the development of polymer-based nanocomposites with high Eb and discharged energy density.

A High Quality-Factor Optical Modulator with Hybrid Graphene-Dielectric Metasurface Based on the Quasi-Bound States in the Continuum.

In this paper, we combine the dielectric metasurface with monolayer graphene to realize a high quality(Q)-factor quasi-BIC-based optical modulator, and the corresponding modulation performances are investigated by using the finite-difference time-domain (FDTD) method, which can be well fitting by the Fano formula based on the temporal couple-mode theory. The results demonstrate that bound states in the continuum (BIC) will turn into the quasi-BIC with high Q-factor by breaking the symmetry of every unit of the metasurface. Meanwhile, the amplitude and bandwidth of transmission based on the quasi-BIC mode can be efficiently adjusted by changing the Fermi energy (EF) of monolayer graphene, and the maximum difference in transmission up to 0.92 is achieved. Moreover, we also discuss the influence of the asymmetry degree to further investigate the modulation effect of graphene on the quasi-BIC mode.

Space-Confined Synthesis of Core-Shell BaTiO3@Carbon Microspheres as a High-Performance Binary Dielectric System for Microwave Absorption.

Binary dielectric composites are viewed as a kind of promising candidate for conventional magnetic materials in the field of microwave absorption. Herein, we demonstrate the successful fabrication of core-shell BaTiO3@carbon microspheres through a space-confined strategy. The electromagnetic properties of BaTiO3@carbon microspheres can be easily tailored by manipulating the relative content of carbon shells. It is confirmed that dielectric loss of these composites mainly benefits from conductivity loss, dipole orientation polarization, and interfacial polarization, and the core-shell configuration shows its positive contribution to the reinforcement of interfacial polarization. When the content of carbon shells is optimized, the as-obtained composite will display excellent microwave-absorption performance due to decent attenuation and well-matched impedance. The strongest reflection loss can reach up to -88.5 dB at 6.9 GHz with the absorber thickness of 3.0 mm, and the qualified bandwidth below -10.0 dB covers 9.0-12.0 GHz, when the thickness is designated at 2.0 mm. Such a performance in the X band is superior to those of most typical binary dielectric systems. More importantly, these BaTiO3@carbon microspheres maintain good performance after being treated under high-temperature and acidic conditions for a long time, manifesting their promising prospect for practical application. It is believed that these results may be helpful for the development of multicomponent dielectric systems as high-performance microwave absorbing materials.

Microwave plasma assisted reduction synthesis of hexagonal cobalt nanosheets with enhanced electromagnetic performances.

In this study, we employed a microwave plasma assisted reduction (MPAR) method to prepare metallic nanoparticles with desirable morphology. Compared with the hydrogen thermal reduction technique, the MPAR technique could greatly maintain the original morphology of self-sacrificing precursors, as well as proving to be highly efficient, energy-saving and pollution-free. Taking ferromagnetic metallic Co as a forerunner, Co nanosheets with inerratic hexagonal morphology were successfully synthesized on a large scale uniformly. The lateral dimension of the achieved Co nanosheets is in the range of 3∼5 µm with tens of nanometers in thickness. The intact hexagonal flaky shape of Co nanosheets is beneficial for improving dielectric loss by increasing electric channels and interfacial polarization. Consequently, the minimum reflection loss could reach up to -71 dB at a thin thickness of 1.2 mm. Furthermore, the effective bandwidth (RL < -10 dB) could be achieved in a wide range of 2.8∼18 GHz by integrating the thickness from 5.0∼1.0 mm, which provides the possibility for applications in electromagnetic shielding and radar stealth fields. It is believed that the MPAR technique is suitable for designing and preparing novel microwave absorbers on the basis of appropriate precursors, providing new opportunities to acquire high-performance microwave absorbers in the future.

Action-Attending Graphic Neural Network.

The motion analysis of human skeletons is crucial for human action recognition, which is one of the most active topics in computer vision. In this paper, we propose a fully end-to-end action-attending graphic neural network (A2GNN) for skeleton-based action recognition, in which each irregular skeleton is structured as an undirected attribute graph. To extract high-level semantic representation from skeletons, we perform the local spectral graph filtering on the constructed attribute graphs like the standard image convolution operation. Considering not all joints are informative for action analysis, we design an actionattending layer to detect those salient action units (AUs) by adaptively weighting skeletal joints. Herein the filtering responses are parameterized into a weighting function irrelevant to the order of input nodes. To further encode continuous motion variations, the deep features learnt from skeletal graphs are gathered along consecutive temporal slices and then fed into a recurrent gated network. Finally, the spectral graph filtering, action-attending and recurrent temporal encoding are integrated together to jointly train for the sake of robust action recognition as well as the intelligibility of human actions. To evaluate our A2GNN, we conduct extensive experiments on four benchmark skeletonbased action datasets, including the large-scale challenging NTU RGB+D dataset. The experimental results demonstrate that our network achieves the state-of-the-art performances.

Effect of Graphene Nanowall Size on the Interfacial Strength of Carbon Fiber Reinforced Composites.

Graphene nanowalls (GNWs) with different sizes (i.e., length and height) were grown directly on the surface of individual carbon fibers (CFs) using a radio frequency plasma-enhanced chemical vapor deposition (RF-PECVD) technique. The size was controlled by varying the deposition time. The GNW-modified CFs were embedded into epoxy resin matrix to prepare a series of carbon-fiber-reinforced composites (CFRCs). The results indicated that GNWs were remarkably effective in improving the interfacial shear strength (IFSS) and interlaminar shear strength (ILSS) of the carbon-fiber-reinforced composites. The enhancement effect on the strength strongly depended on the size of GNWs. It increased with the increase in the GNWs’ size and reached the maximum upon the incorporation of GNWs that were grown for 45 min. Noticeable increases of 222.8% and 41.1% were observed in IFSS and ILSS, respectively. The enhancement mechanism was revealed by means of scanning electron microscope (SEM) fractography analysis. However, further increase of GNW size led to no more improvement in the shear strength. It could result from the increased defect concentration and wrinkle size in the GNWs, which deteriorated the strength.

Microstructure Evolution and Mechanical Behavior of 2219 Aluminum Alloys Additively Fabricated by the Cold Metal Transfer Process.

In this research, four different welding arc modes including conventional cold metal transfer (CMT), CMT-Pulse (CMT-P), CMT-Advanced (CMT-ADV), and CMT pulse advanced (CMT-PADV) were used to deposit 2219-Al wire. The effects of different arc modes on porosity, pore size distribution, microstructure evolution, and mechanical properties were thoroughly investigated. The statistical analysis of the porosity and its size distribution indicated that the CMT-PADV process gave the smallest pore area percentage and pore aspect ratio, and had almost no larger pores. The results from optical microscopy, scanning electron microscopy, and fractographic morphology proved that uniform and fine equiaxed grains, evenly distributed Al2Cu second phase particles were formed during the CMT-PADV process. Furthermore, the X-ray diffraction test ascertained that the CMT-PADV sample had the smallest lattice parameter and the highest solute Cu content. Besides, the tensile strength could reach 283 MPa, the data scattering was the smallest, and the strength scattering of the sample in the horizontal direction was the shortest. In addition, the strength properties were nearly isotropic, with only 5 MPa difference in the vertical and horizontal directions. The above mentioned results indicated that the mechanical properties of 2219 aluminum alloy was improved using the CMT-PADV arc mode.

Identification of oligopeptide-binding protein (OppA) and its role in the virulence of Streptococcus suis serotype 2.

The oligopeptide permease (Opp) cassette, an oligopeptide transport system belongs to the superfamily of ATP-binding cassette (ABC) transporter, is widely distributed in bacteria, including Streptococcus suis (S. suis). It is encoded by the opp operon containing oppA, oppB, oppC, oppD, and oppF. In addition to the uptake of peptide, the oppA gene also plays an important role in virulence of many pathogens. In this study, an oppA homologue from the highly virulent S. suis serotype 2 (S. suis 2) strain 05ZYH33 was identified. Flow cytometry and Western blot confirmed that OppA is a surface immunogenic protein and is expressed during S. suis 2 infection. To explore the role of oppA in S. suis 2 growth and pathogenicity, an isogenic 05ZYH33 mutant of oppA (△oppA) was obtained by homologous recombination. Although the complementary strain was not obtained due to the △oppA strain is not transformable, the current data revealed that deletion of the oppA gene in S. suis 2 has greatly affected its growth and virulence. Our data revealed that the growth rate is significantly slow for the △oppA. Adherence of the △oppA strain to human epithelial cells is greatly reduced comparing to the wild strain. Mouse infection experiment showed that inactivation of oppA greatly attenuated the high pathogenicity of S. suis 2. The observed results suggest that OppA is a surface-exposed protein and plays important roles in the growth and pathogenicity of S. suis 2.

Streptococcus suis DivIVA Protein Is a Substrate of Ser/Thr Kinase STK and Involved in Cell Division Regulation.

Streptococcus suis serotype 2 is an important swine pathogen and an emerging zoonotic agent that causes severe infections. Recent studies have reported a eukaryotic-like Ser/Thr protein kinase (STK) gene and characterized its role in the growth and virulence of different S. suis 2 strains. In the present study, phosphoproteomic analysis was adopted to identify substrates of the STK protein. Seven proteins that were annotated to participate in different cell processes were identified as potential substrates, which suggests the pleiotropic effects of stk on S. suis 2 by targeting multiple pathways. Among them, a protein characterized as cell division initiation protein (DivIVA) was further investigated. In vitro analysis demonstrated that the recombinant STK protein directly phosphorylates threonine at amino acid position 199 (Thr-199) of DivIVA. This effect could be completely abolished by the T199A mutation. To determine the specific role of DivIVA in growth and division, a divIVA mutant was constructed. The ΔdivIVA strain exhibited impaired growth and division, including lower viability, enlarged cell mass, asymmetrical division caused by aberrant septum, and extremely weak pathogenicity in a mouse infection model. Collectively, our results reveal that STK regulates the cell growth and virulence of S. suis 2 by targeting substrates that are involved in different biological pathways. The inactivation of DivIVA leads to severe defects in cell division and strongly attenuates pathogenicity, thereby indicating its potential as a molecular drug target against S. suis.

Hydrothermal synthesis of stable metallic 1T phase WS2 nanosheets for thermoelectric application.

Two-dimensional materials have gained great attention as a promising thermoelectric (TE) material due to their unique density of state with confined electrons and holes. Here, we synthesized 1T phase tungsten disulfide (WS2) nanosheets with high TE performance via the hydrothermal method. Flexible WS2 nanosheets restacked thin films were fabricated by employing the vacuum filtration technique. The measured electrical conductivity was 45 S cm-1 with a Seebeck coefficient of +30 µV K-1 at room temperature, indicating a p-type characteristic. Furthermore, the TE performance could be further improved by thermal annealing treatment. It was found the electrical conductivity could be enhanced 2.7 times without sacrificing the Seebeck coefficient, resulting in the power factor of 9.40 µW m-1 K-2. Moreover, such 1T phase WS2 nanosheets possess high phase stability since the TE properties maintained constant at least half one year in the air atmosphere. Notably, other kinds of 1T phase transitional metal dichalcogenides (TMDCs) with excellent TE performance also could be imitated by using the procedure in this work. Finally, we believe a variety of materials based on 1T phase TMDCs nanosheets have great potential as candidate for future TE applications.

2D/3D perovskite hybrids as moisture-tolerant and efficient light absorbers for solar cells.

The lifetime and power conversion efficiency are the key issues for the commercialization of perovskite solar cells (PSCs). In this paper, the development of 2D/3D perovskite hybrids (CA2PbI4/MAPbIxCl3-x) was firstly demonstrated to be a reliable method to combine their advantages, and provided a new concept for achieving both stable and efficient PSCs through the hybridization of perovskites. 2D/3D perovskite hybrids afforded significantly-improved moisture stability of films and devices without encapsulation in a high humidity of 63 ± 5%, as compared with the 3D perovskite (MAPbIxCl3-x). The 2D/3D perovskite-hybrid film did not undergo any degradation after 40 days, while the 3D perovskite decomposed completely under the same conditions after 8 days. The 2D/3D perovskite-hybrid device maintained 54% of the original efficiency after 220 hours, whereas the 3D perovskite device lost all the efficiency within only 50 hours. Moreover, the 2D/3D perovskite hybrid achieved comparable device performances (PCE: 13.86%) to the 3D perovskite (PCE: 13.12%) after the optimization of device fabrication conditions.

Palladium-catalyzed cycloisomerizations of (Z)-1-iodo-1,6-dienes: iodine atom transfer and mechanistic insight to alkyl iodide reductive elimination.

A palladium-catalyzed iodine atom transfer cycloisomerization of (Z)-1-iodo-1,6-diene has been developed, which provides a facile method to construct six-memebered heterocycles bearing an alkyl iodide group. The ligand screening shows that both the type and the quantity of ligand impose significant influences on this transformation, and the combination of 30 mol % 1,1'-bis(diphenylphosphino)ferrocene (DPPF) and 10 mol % Pd(OAc)(2) is the optimal choice. The catalytic cycle, consisting of oxidative addition of Pd(0) to vinyl iodide, intramolecular alkene insertion, and alkyl iodide reductive elimination, has been proposed and eventually supported by convincing evidence from a series of control experiments. More importantly, these control experiments disclose some features of the event of alkyl iodide reductive elimination: (1) this reductive elimination is proved to be a stereospecific process; and (2) both alkyl iodide oxidative addition and reductive elimination are not effected by a TEMPO additive. Besides its ability to undergo oxidative addition, the catalyst (palladium + DPPF) could also promote a radical transfer process. The findings described in this paper will be helpful for further development of the metal-catalyzed formation of a carbon-halide bond.

Amine-catalyzed (3+n) annulations of 2-(acetoxymethyl)buta-2,3-dienoates with 1,n-bisnucleophiles (n = 3-5).

A tertiary amine-catalyzed formal (3+n) annulation of 2-(acetoxymethyl)buta-2,3-dienoate with 1,n-binucleophiles has been developed, which provides a facile entry to heterocyclic compounds. The mechanism, involving tandem S(N)2'-S(N)2' substitution and Michael addition, has also been established.

Rhodium-catalyzed cycloaddition of 1,6-enynes with 2-bromophenylboronic acids: synthesis of a multi-substituted dihydronaphthalene scaffold.

A formal [2 + 2 + 2] cycloaddition of a 1,6-enyne with 2-bromophenylboronic acid has been realized to construct a multi-substituted dihydronaphthalene scaffold, in which the direct reductive elimination mechanism of aryl-Rh(iii)-C(sp(3)) species has been established to form an aryl-C(sp(3)) bond.

Nitric oxide induces promyelocytic cell growth arrest and apoptosis through deactivation of Akt pathway.

It is NO that mediates the inhibitory effect of IFN-gamma, MIP-1alpha and TNFalpha on hematopoiesis. However, the mechanism for NO effect on the hematopoietic system is likely to not clear. In the current work, we demonstrates that NO can directly suppress the colony formation of granulocyte/macrophage in vitro. Using a granulocyte/macrophage progenitor (GMP) model, HL-60 cell line, we show that NO inhibits the proliferation of HL-60 cells by inducing G0/G1 arrest and apoptosis in a dose- and time-dependent manner. Exposure of HL-60 cells to 1mM SNP for 2-48h results in marked decrease in Akt activation and Bad phosphorylation. Constitutively active Akt overexpression reduces NO-induced apoptosis and cell cycle arrest in HL-60 cells. A further investigation on apoptosis related protein shows that NO induces Bid cleavage and Bax expression but down-regulates the expression of Bcl-2 and Bcl-xL. We also demonstrate here that G0/G1 arrest is resulted from NO-induced disruption of cell cycle balance, which is mediated by up-regulation of p21(waf/cip1), p27(kip1) and down-regulation of cyclin D1, cyclin E. In brief, NO-induced apoptosis and G0/G1 arrest is mediated through regulation of apoptosis and cell cycle related protein, which may depend on Akt deactivation by NO, ultimately led to its inhibitory effect on hematopoiesis.

[Differential gene expression profile of keloids: a study with cDNA microarray].

OBJECTIVE: To investigate the differentially expressed genes in keloids in comparison with normal skin using cDNA microarray. METHODS: The cDNA microarray consisting of 8064 clones of human genes was employed to detect and screen the differentially expressed genes in keloid and normal skin tissues. Semi-quantitative RT-PCR was applied to verify the results of gene microarray. RESULTS: Totally 277 differentially expressed genes were identified in keloids in comparison with normal skin tissue, including 163 up-regulated genes and 114 down-regulated ones according to the designed data filter criteria. These differentially expressed genes belonged to 26 different functional gene families involving different biological processes. RT-PCR yielded results were consistent with those of microarray study. CONCLUSION: A variety of genes are involved in the formation of keloids. The 277 differentially expressed genes comprise the differential gene expression profile of keloids and describe the general changes in the gene expressions in keloid at transcriptional level. Further analysis of the identified genes might help reveal the molecular mechanism of abnormal scarring.

Diagnosis and treatment of pancreatolithiasis: report of 16 cases.

BACKGROUND: Pancreatolithiasis is rarely recognized clinically. This study was undertaken to assess the value of ultrasonography in the diagnosis of 16 patients with pancreatolithiasis and its treatment with pancreatolithotomy plus side-to-side pancreaticojejunostomy. Extracorporeal shock wave lithotripsy was also used in some patients. METHODS: In the 16 patients with pancreatolithiasis treated at our hospital from 1977 to June 2002, 3 patients were complicated by pancreatic cancer, 2 pancreatic head cyst, and 1 choledochal cyst. Ten patients underwent operation, 3 received endoscopic sphincterotomy (EST), and 3 refused operation and left the hospital. RESULTS: Epigastric pain was the major symptom of the disease. Ultrasonography was the best choice for the diagnosis of the disease in addition to CT for determining characteristics and location of pancreatolithiasis associated with pancreatic cancer, ERCP for showing pancreatic stone, and EST for detecting stone in the pancreatic head. Pancreatolithotomy plus side-to-side pancreaticojejunostomy was used for the treatment of pancreatolithiasis. CONCLUSIONS: Ultrasonography is the first choice for the diagnosis of pancreatolithiasis. Pancreatolithotomy plus side-to-side pancreaticojejunostomy is the best choice for the treatment of pancreatolithiasis. CT is of great value in determining characteristics and locations of pancreatolithiasis associated with pancreatic cancer. For patients with pancreatolithiasis associated with pancreatic cancer, surgical treatment should follow the principles of individualized therapy.

[Impact of early-stage hepatic ischemia-reperfusion injury on other organs of rats].

OBJECTIVE: To investigate the influence of hepatic ischemia-reperfusion on other organs of rats during the early stage of injury. METHODS: Twenty-five healthy male SD rats were randomized equally into 5 groups according to the different time points in the course of hepatic vascular occlusion and reperfusion, namely pre-occlusion, the end of occlusion, and after 0.5, 2.0 and 6.0 h reperfusion, respectively. In each group the rats were killed to obtain samples at the specified time points. The contents of malondialdehyde (MDA) and superoxide dismutase (SOD) in the lung, kidney, pancreas and heart were measured in pre-occlusion and 6-hour reperfusion groups. The triphosphate (ATPase) activity in heart tissues, the contents of MDA and the activity of SOD in blood and the blood biochemistry were observed in different groups. RESULTS: The activity of SOD and ATPase were decreased (P<0.05) after the ischemia-reperfusion as compared with those before ischemia, but the contents of MDA, ALT, AST BUN, AMY and CK-MB increased significantly (P<0.05). CONCLUSION: Liver ischemia-reperfusion can induce injury to other organs at the early stage of reperfusion.

[Three-dimensional dynamic contrast-enhanced magnetic resonance angiography in liver transplantation].

OBJECTIVE: To investigate the clinical value of three-dimensional dynamic contrast-enhanced magnetic resonance (MR) angiography in the liver transplantation. METHODS: MR scanning was performed both before and after the operation in 9 patients elected for liver transplantation, and after three-dimensional reconstruction at a computer workstation, the three- dimensional images of the inferior vena cava, hepatic veins, portal vein and bile duct were obtained. RESULTS: The three- dimensional images could be rotated in space to show the size, shape, lining of the veins and anatomic relationships between each other. CONCLUSION: Three-dimensional dynamic contrast-enhanced MR angiography can be of value in liver transplantation.

Multiple organ injury at early stage of intestinal and hepatic ischemia-reperfusion in rats.

OBJECTIVE: To investigate the early-stage multiple organ injuries in rats subjected to intestinal and hepatic ischemia-reperfusion. METHODS: Seventy-five normal male Wistar rats were randomized equally into hepatic ischemia, intestinal ischemia and intestinal-hepatic ischemia groups. Before and at the end of occlusion (45 min), as well as at the time points of 0.5, 2.0 and 6.0 h during the reperfusion, respectively, 5 rats from each group were killed to obtain samples for determination of the contents of malondialdehyde (MDA), superoxide dismutase (SOD) in the blood, lung, kidney, pancreas and heart tissues, along with blood urea nitrogen (BUN), amylase (AMY), and creatine kinase MB (CK-MB). RESULTS: The activity of SOD was decreased (P<0.05) and MDA, BUN, AMY and CK-MB levels increased significantly (P<0.05) after ischemia-reperfusion as compared with those before ischemia. CONCLUSIONS: Intestinal and hepatic ischemia-reperfusion can induce injury of multiple organs at early stage. With the same duration of ischemia-reperfusion, intestinal ischemia may induce severer injury than hepatic ischemia.