Cubic CoSe2@carbon as polysulfides adsorption-catalytic mediator for fast redox kinetics and advanced stability lithium-sulfur batteries.

Although lithium-sulfur batteries (LSBs) are an attractive next-generation rechargeable battery with high theoretical energy density (2600 Wh kg-1) and specific capacity (1675 mA h g-1), the shuttle of soluble lithium polysulfides (LiPSs) is still the protruding obstacle to accelerate the redox reaction of LSBs. Here, cubic cobalt diselenide@carbon (CoSe2@C) derived from zeolite imidazole framework-67 (ZIF-67) was employed as the functional coating of polypropylene (PP) separator to efficiently adsorb and catalyze polysulfides, inhibit "shuttle effect" and improve the electrochemical reaction kinetics of LSBs. The CoSe2@C offers larger mesopore proportion of 77.19 % and abundant active sites to ensure space as a secondary reaction region, and infiltration of electrolyte and rapid transport of Li+. The involved adsorption and catalysis effect are discussed by static adsorption experiment, XPS, and Li2S nucleation kinetics analysis. The results show that CoSe2@C exhibits strong adsorption effect and catalytic activity on LiPSs, and CoSe2@C/PP cells display fast Li+ diffusion and improved redox kinetics (high Li2S nucleation peak current of 0.27 mA and deposition capacity of 148.46 mA h g-1). Ascribe to these advantages, the CoSe2@C/PP cell provides an initial discharge specific capacity of 1335.01 mA h g-1 at 0.1 C and a fine reversible capacity at 5.0 C, and achieves stable and durable lifespan with an average capacity decay rate of 0.12 % over 400 cycles at 0.5 C. This work could promote the practical application of metal selenides in the key components and devices for LSBs.

Bottom Electrode Effects on Piezoelectricity of Pb(Zr0.52,Ti0.48)O3 Thin Film in Flexible Sensor Applications.

Piezoelectric thin films grown on a mechanical, flexible mica substrate have gained significant attention for their ability to convert mechanical deformation into electrical energy though a curved surface. To extract the generated charge from the PZT thin films, bottom electrodes are typically grown on mica substrates. However, this bottom electrode also serves as a buffering layer for the growth of PZT films, and its impact on the piezoelectric properties of PZT thin films remains understudied. In this work, the effect of Pt and LaNiO3 bottom electrodes on the piezoelectric effect of a Pb(Zr0.52,Ti0.48)O3 thin film was investigated. It was observed that the PZT thin films on LNO/Mica substrate possessed weaker stress, stronger (100) preferred orientation, and higher remanent polarization, which is beneficial for a higher piezoelectric response theoretically. However, due to insufficient grain growth resulting in more inactive grain boundaries and lattice imperfections, the piezoelectric coefficient of the PZT thin film on LNO/Mica was smaller than that of the PZT thin film on a Pt/Mica substrate. Therefore, it is concluded that, under the current experimental conditions, PZT films grown with Pt as the bottom electrode are better suited for applications in flexible piezoelectric sensor devices. However, when using LNO as the bottom electrode, it is possible to optimize the grain size of PZT films by adjusting the sample preparation process to achieve piezoelectric performance exceeding that of the PZT/Pt/Mica samples.

Association between obesity indicators and cardiometabolic disease in Chinese adults.

BACKGROUND: Obesity is an established risk factor for cardiometabolic disease. Different measurements of obesity with cardiometabolic disease have been compared in recent studies in Western countries. However, obesity-related criteria for the Chinese population differ from the standard World Health Organization guidelines, and similar research in Chinese adults is limited. MEASURES: Data were obtained from a comprehensive intervention project involving a community population with cardiovascular and cerebrovascular risk factors in Shenzhen in 2015. A total of 4,000 participants (1,605 men and 2,395 women) with a mean age of 56.01±9.78 years were included in this study. Categorical data are reported as percentages, and continuous data are reported as mean ± standard deviation. Logistic regression analyses were conducted to examine the associations of body mass index (BMI), waist circumference (WC), and neck circumference (NC) with hypertension, diabetes, and dyslipidemia among Chinese adults. RESULTS: The participants had a mean BMI of 24.25±3.33 kg/m2, mean NC of 33.59±4.16 cm, and mean WC of 82.44±9.84 cm (men: 85.46±9.10 cm, women: 80.40±9.81 cm). Blood pressure, plasma glucose, and lipid levels in the BMI, WC, and NC groups were statistically significant (p < 0.05). BMI, WC, and NC were positively correlated with systolic blood pressure, diastolic blood pressure, fasting plasma glucose, total cholesterol, and triglyceride and negatively correlated with low-density lipoprotein cholesterol (p < 0.05), while the risk of hypertension, diabetes, and dyslipidemia increased with an increase in BMI, WC, and NC (p < 0.05). One SD of BMI, WC, and NC resulted in an increase of 41%, 22%, and 31% risk of hypertension; 45%, 34%, and 47% risk of diabetes; and 37%, 32%, and 23% risk of dyslipidemia, respectively. CONCLUSIONS: Compared to BMI and NC, WC was more strongly associated with cardiometabolic diseases in Chinese adults.

Improving the DC Dielectric Properties of XLPE with Appropriate Content of Dicumyl Peroxide for HVDC Cables Insulation.

In this research, crosslinked polyethylene (XLPE) is developed with selective content of dicumyl peroxide (DCP), and the influence of microstructural properties and chemical composition on the mechanical and direct current (DC) dielectric properties are investigated. The measurements for the microstructural analysis are taken by gel permeation chromatography (GPC), differential scanning calorimetry (DSC), gel content test and Fourier transform infrared (FTIR). The mechanical properties of XLPE are evaluated by hot-set test. The results of microstructural and chemical composition show that the increase in DCP content increases the crosslinking degree from 74.3% to 81.6%, reduces the crystallinity/lamella thickness from 36.8% to 35.5%/7.6-7.1 nm, reduces the average molecular weight between two crosslinks by 0.01 kg/mol and reduces the oxidation level/carbonyl index. The increase in DCP in XLPE samples decreases the permanent elongation from 2.2% to 0% and elongation rate from 300% to 80% of the cable insulation. The rise in DCP content increases the crosslinking degree due to which the DC resistivity and activation energy is increased. The DC breakdown strength at 30-90 °C is increased due to the increase in crosslinking degree and reduction in carbonyl index/oxidation level. The space charge accumulation is measured at 30 °C under 20-60 kV/mm, resulting in less homo-charges and hetero-charges with the increase in DCP. It is proven that the role of appropriate DCP content is vital in increasing the DC dielectric performance, internal material characteristics and mechanical performance of XLPE.

High Energy Density and Temperature Stability in PVDF/PMMA via In Situ Polymerization Blending.

Dielectrics with improved energy density have long-standing demand for miniature and lightweight energy storage capacitors for electrical and electronic systems. Recently, polyvinylidene fluoride (PVDF)-based ferroelectric polymers have shown attractive energy storage performance, such as high dielectric permittivity and high breakdown strength, and are regarded as one of the most promising candidates. However, the non-negligible energy loss and inferior temperature stability of PVDF-based polymers deteriorated the energy storage performance or even the thermal runaway, which could be ascribed to vulnerable amorphous regions at elevated temperatures. Herein, a new strategy was proposed to achieve high energy density and high temperature stability simultaneously of PVDF/PMMA blends by in situ polymerization. The rigidity of the amorphous region was ideally strengthened by in situ polymerization of methyl methacrylate (MMA) monomers in a PVDF matrix to obtain PVDF/PMMA blends. The atomic force microscopic study of the microstructure of etched films showed the ultra-homogenous distribution of PMMA with high glass transition temperature in the PVDF matrix. Consequently, the temperature variation was remarkably decreased, while the high polarization response was maintained. Accordingly, the high energy density of ∼8 J/cm3 with ∼80% efficiency was achieved between 30 and 90 °C in PVDF/PMMA films with 39-62% PMMA content, outperforming most of the dielectric polymers. Our work could provide a general solution to substantially optimize the temperature stability of dielectric polymers for energy storage applications and other associated functions.

Achieving Good Temperature Stability of Dielectric Constant by Constructing Composition Gradient in (Pb1-x,Lax)(Zr0.65,Ti0.35)O3 Multilayer Thin Films.

Ferroelectrics with a high dielectric constant are ideal materials for the fabrication of miniaturized and integrated electronic devices. However, the dielectric constant of ferroelectrics varies significantly with the change of temperature, which is detrimental to the working stability of electronic devices. This work demonstrates a new strategy to design a ferroelectric dielectric with a high temperature stability, that is, the design of a multilayer relaxor ferroelectric thin film with a composition gradient. As a result, the fabricated up-graded (Pb,La)(Zr0.65,Ti0.35)O3 multilayer thin film showed a superior temperature stability of the dielectric constant, with variation less than 7% in the temperature range from 30 °C to 200 °C, and more importantly, the variation was less than 2.5% in the temperature range from 75 °C to 200 °C. This work not only develops a dielectric material with superior temperature stability, but also demonstrates a promising method to enhance the temperature stability of ferroelectrics.

Phase Field Modeling on By-Product Migration in Crosslinking Polymers for HVDC Cable Insulation Applications.

Cross-linking by-products has been considered as one of the crucial factors for dielectric properties of cross-linked polyethylene, which plays an important role in the insulation performance of high voltage direct current (HVDC) cables. It migrates across cable insulation incorporating space charge effect, temperature variation of conductivity, etc., which makes it a long-standing puzzle of manipulating the electric field distribution for HVDC cable insulation, especially with the increasing voltage level. Nevertheless, there still lacks a theoretical model describing the migration of the by-products, especially for cable insulation with sizeable dimensions. In this article, a phase field model is established to simulate the migration of acetophenone (i.e., one of the by-products) through calculating the free energy landscape considering the competition between the diffusion driven by concentration gradient and the uphill diffusion caused by by-product aggregation. The results show that the time-dependence migration during degassing leads to an uneven distribution of acetophenone across the cable insulation, which is in good coincidence with the measured results for a full-size cable. Accordingly, the distortion of the electric field in HVDC cable insulation due to the radial distribution variation of acetophenone has been estimated regarding the relationship between by-product content and conductivity, and a method of manipulating the distribution of acetophenone is proposed to optimize the distribution of the electric field in cable insulation. Our work provides a numerical approach for the simulation of by-product migration in crosslinked polymers for insulation applications.

Charge Accumulation in the Homo-Crosslinked-Polyethylene Bilayer.

The homo-crosslinked-polyethylene (H-XLPE) bilayer simplifies the returned insulation structure of the factory joint in submarine cables, and its dielectric property is key to the reliability of the power transmission system. In this paper, we investigated the charge accumulation phenomenon in a secondary thermocompression H-XLPE bilayer using the pulse electro-acoustic method. The charge accumulation reduces its overall breakdown strength when compared with XLPE. According to X-ray diffraction measurement and thermal analysis results, the specimen forms a homo-junction region between the bilayers, which has overlapping spherulites with a thick lamella, high crystallinity, and high surface free energy. The charge accumulation can be ascribed to fused lamellas and the crystal imperfection of the homo-junction region, which restricts the charge transport process and exhibits a higher number of deep traps. This study emphasizes the importance of the homo-junction region in the H-XLPE bilayer, which should be considered in the design and operation of factory joint insulation.

Microstructure, Mechanical and Tribological Properties of Si3N4/Mo-Laminated Composites.

(1) Background: the applications of ceramic materials in a friction pair and a moving pair are limited, just because of their poor toughness and unsatisfactory tribological characteristics. In view of this, Mo as a soft metal layer was added into a Si3N4 matrix to improve its toughness and tribological characteristics. (2) Methods: The microstructure and metal/ceramic transition layer were examined using X-ray diffraction, scanning electron microscope, electron dispersive X-ray spectroscopy, and Vickers hardness. Bending strength and fracture toughness were also measured. Tribological characteristics were obtained on the pin-on-disc wear tester. (3) Results: It can be found that the multilayer structure could improve the fracture toughness of laminated composite compared with single-phase Si3N4, but the bending strength was significantly reduced. Through microstructure observation, the transition layer of Si3N4/Mo-laminated composite was revealed as follows: Si3N4→MoSi2→Mo5Si3→Mo3Si→Mo. Moreover, the addition of the Mo interface to silicon nitride ceramic could not significantly improve the tribological properties of Si3N4 ceramic against titanium alloy in seawater, and the friction coefficients and wear rates of the sliding pairs increased with the increase in load. (4) Conclusions: The process failed to simultaneously improve the comprehensive mechanical properties and tribological performance of Si3N4 ceramic by adding Mo as the soft interfacial layer. However, the utilization of metal interfacial layers to enhance the toughness of ceramics was further recognized and has potential significance for the optimization of ceramic formulation.

Direct Evidence of Ice Crystallization Inhibition by Dielectric Relaxation of Hydrated Ions.

In this paper, the inhibition effect of an alternative current (AC) electric field on ice crystallization in 0.9 wt % NaCl aqueous solution was confirmed thermodynamically with characterization. An innovative experimental and analytical method, combining differential scanning calorimeter (DSC) measurement with an externally applied electric field was created by implanting microelectrodes in a sample crucible. It was found that the ice crystallization, including pure ice and salty ice, was obviously inhibited after field cooling with an external AC electric field in a frequency range of 100 k-10 MHz, and the crystallization ratio was related to frequency. Compared with non-field cooling, the crystallization ratio of ice crystals was reduced to less than 20% when E = 57.8 kV/m and f = 1 MHz. The dielectric spectrum results show that this inhibition effect of an alternating electric field on ice crystal growth is closely related to the dielectric relaxation process of hydrated ions.

Trirelaxor Ferroelectric Material with Giant Dielectric Permittivity over a Wide Temperature Range.

Advanced ferroelectrics with a combination of large dielectric response and good temperature stability are crucial for many technologically important electronic devices and electrical storage/power equipment. However, the two key factors usually do not go hand in hand, and achieving high permittivity is normally at the expense of sacrificing temperature stability. This trade-off relation is eased but not fundamentally remedied using relaxor-type materials which are known to have a diffuse permittivity peak at their relaxor transition temperatures. Here, we report an anomalous trirelaxor phenomenon in a barium titanate system and show that it can lead to a giant dielectric permittivity (εr ≈ 18 000) over a wide temperature range (Tspan ≈ 34K), which successfully overcomes a long-standing permittivity-stability trade-off. Moreover, the enhancement in the dielectric properties also yields a desired temperature-insensitive electrocaloric performance for the trirelaxor ferroelectrics. Microstructure characterization and phase-field simulations reveal a mixture of tetragonal, orthorhombic, and rhombohedral polar nanoregions over a broad temperature window in trirelaxor ferroelectrics, which is responsible for this combination of giant dielectric permittivity and good temperature stability. This finding provides an effective approach in designing advanced ferroelectrics with high performance and thermal stability.

Crosslinking Dependence of Direct Current Breakdown Performance for XLPE-PS Composites at Different Temperatures.

In this paper, crosslinked polyethylene-polystyrene (XLPE-PS) composites with different degrees of crosslinking were fabricated by using different crosslinking agent contents and their direct current (DC) breakdown performance at 30~90 °C was investigated. Results show that with the increase of the degree of crosslinking, the crystallinity of XLPE-PS composites decreases gradually, but their DC breakdown strength demonstrates an increasing trend at 30~90 °C and the enhancement also increases with the rise of temperature. And as the degree of crosslinking increases, the elastic modulus of XLPE-PS composites is reduced and the loss tangent peak temperature decreases but the peak shifts to a lower value, which reveals the suppression of the relaxation process for crystallites. It is believed that high DC breakdown strength with good temperature stability for XLPE-PS composites with a larger degree of crosslinking is attributable to the presence of PS and suppression in the formation of crystallites due to crosslinking.

Enhanced Temperature Stability of High Energy Density Ferroelectric Polymer Blends: The Spatial Confinement Effect.

Thermal stability of polymer structure is a key to achieve stable energy density at elevated temperature for ferroelectric-polymer-based capacitors. Here, a poly (vinylidene fluoride) / polymethyl methacrylate (PMMA) blend with a stabilized spherulite structure displaying steady energy density around 7.8-9.8 J cm-3 across the temperature range up to 70 °C is reported, which outperforms most neat ferroelectric polymers at elevated temperature. The microstructure of the blend observed by atomic force microscopy exhibits an alternating lamellar structure (crystalline/mixed amorphous layers) within spherulites, which might be rationalized by PMMA being gradually expelled from the spherulite and finally staying between PVDF lamellae during crystallization. The structure with rigid amorphous layers can induce a spatial confinement effect of chain motion and structural change under thermal stress, which is evidenced by temperature-insensitive long period in small-angle X-ray scattering measurements. The enhanced thermal stability of energy storage can be attributed to the constraint on free volume and carrier transportation caused by the spatial confinement. Our findings provide a strategy to attain temperature-stable high-energy-density ferroelectric polymers for energy storage capacitors.

Enhanced High-Temperature DC Dielectric Performance of Crosslinked Polyethylene with a Polystyrene Pinning Structure.

In this paper, we propose a method on improving direct current (DC) dielectric performance by designing a polystyrene (PS) pinning crosslinked polyethylene (XLPE) for the application of insulation materials on high voltage direct current (HVDC) extruded cable. Electrical experimental results show that the addition of PS (1-5 phr, parts per hundreds of resin) can significantly reduce DC conductivity and increase DC breakdown strength of XLPE in the test temperature range of 30-90 °C. Microstructure investigation shows PS distributed as particles could participate in the formation of a crosslinking network with the help of a crosslinking agent, thus forming a polymer pinning structure at the interface between XLPE and PS. It is believed that such a special design strengthens the structure of XLPE, which leads to the improved DC dielectric performance at elevated temperatures. Our findings may contribute a new solution for developing HVDC cable insulation materials.

Enhancing the Energy Density of Tricritical Ferroelectrics for Energy Storage Applications.

Recently, tricritical ferroelectrics have been drawn tremendous attention, owing to their ultrahigh dielectric permittivities of up to εr > 5 × 104, and their consideration for prototype materials in the development of high-performance energy storage devices. Nevertheless, such a materials system suffers from the disadvantage of low breakdown strength, which makes its energy density far from the satisfactory level for practical application. In this paper, a material-modification approach has been reported, for improving the dielectric strength for tricritical ferroelectric materials Ba(Ti1-xSnx)O3 (BTS) through doping with Bi1.5ZnNb1.5O7 (BZN) additives. The results suggest that the electric strength has been largely improved in the modified tricritical ferroelectric material (BTSx-yBZN), and the associated energy density reaches Ue = 1.15 J/cm³. Further microstructure investigation indicates that the modified tricritical ferroelectric material exhibits homogenous fine grains with perovskite structure in crystal symmetry, and the BZN may help to form a special structure that could enhance the breakdown strength. The findings may advance the material design and development of high-energy storage materials.

Temperature Dependence of Mechanical, Electrical Properties and Crystal Structure of Polyethylene Blends for Cable Insulation.

There is a long-standing puzzle concerning whether polyethylene blends are a suitable substitution for cable-insulation-used crosslinking polyethylene (XLPE) especially at elevated temperatures. In this paper, we investigate temperature dependence of mechanical, electrical properties of blends with 70 wt % linear low density polyethylene (LLDPE) and 30 wt % high density polyethylene (HDPE) (abbreviated as 70 L-30 H). Our results show that the dielectric loss of 70 L-30 H is about an order of magnitude lower than XLPE, and the AC breakdown strength is 22% higher than XLPE at 90 °C. Moreover, the dynamic mechanical thermal analysis (DMA) measurement and hot set tests suggest that the blends shows optimal mechanical properties especially at high temperature with considerable temperature stability. Further scanning electron microscope (SEM) observation and X-ray diffraction (XRD) analysis uncover the reason for the excellent high temperature performance and temperature stability, which can be ascribed to the uniform fine-spherulite structure in 70 L-30 H blends with high crystallinity sustaining at high temperature. Therefore, our findings may enable the potential application of the blends as cable insulation material with higher thermal-endurance ability.

Power Flow in a Large-Core Multimode Fiber under External Perturbation and its Applications.

Large core optical multimode fiber provides benefits such as a large light-coupling tolerance, easy handling, and delivery of higher light power without undesirable nonlinear effects. In this research, we exploit the effects of external perturbation on the power flow within the large core fiber and present two relevant applications, namely a perturbation sensor and a doughnut beam tuner. Since conventional multimode fiber power flow model does not take into consideration the perturbation effect, we modify the power flow model so that the influence of time varying perturbation can be theoretically analyzed. Based on our theory, we further conduct the numerical simulation and experiments on these two applications. For the fiber vibration sensor, the proposed numerical model shows that the sensor sensitivity depends on the intensity profile of the launched beam and also the higher-order harmonics that were not reported previously can become interferences to affect the signal. For the beam tuner application, we prove both theoretically and experimentally that the doughnut intensity profile at the fiber output can be tuned in real-time by applying external perturbations to the fiber. We expect that the results can be useful to further exploit the external perturbation on large core fiber in various applications.

Enhancing dielectric permittivity for energy-storage devices through tricritical phenomenon.

Although dielectric energy-storing devices are frequently used in high voltage level, the fast growing on the portable and wearable electronics have been increasing the demand on the energy-storing devices at finite electric field strength. This paper proposes an approach on enhancing energy density under low electric field through compositionally inducing tricriticality in Ba(Ti,Sn)O3 ferroelectric material system with enlarged dielectric response. The optimal dielectric permittivity at tricritical point can reach to εr = 5.4 × 104, and the associated energy density goes to around 30 mJ/cm3 at the electric field of 10 kV/cm, which exceeds most of the selected ferroelectric materials at the same field strength. The microstructure nature for such a tricritical behavior shows polarization inhomogeneity in nanometeric scale, which indicates a large polarizability under external electric field. Further phenomenological Landau modeling suggests that large dielectric permittivity and energy density can be ascribed to the vanishing of energy barrier for polarization altering caused by tricriticality. Our results may shed light on developing energy-storing dielectrics with large permittivity and energy density at low electric field.

Investigation on sensitivity enhancement for optical fiber speckle sensors.

We present a detailed theoretical and experimental study on the sensitivity enhancement for multimode fiber (MMF) speckle sensor. Using mode coupling theory, we derive an expression showing that the sensitivity of the MMF speckle sensor depends on the intensity profile of the MMF modes. Particularly, we use our theory to study the influence of the spatial filtering window on the sensitivity, and the experimental results have found a good agreement with the theory. Our results suggest that the sensitivity of an MMF speckle sensor can be greatly enhanced by adjusting the size and location of the spatial filtering window. An 80-fold improvement on sensitivity was achieved in our experiment, as compared with the conventional MMF speckle sensor with the filtering window placed at the center of the speckle field.

Influences of Electromagnetic Energy on Bio-Energy Transport through Protein Molecules in Living Systems and Its Experimental Evidence.

The influences of electromagnetic fields (EMFs) on bio-energy transport and its mechanism of changes are investigated through analytic and numerical simulation and experimentation. Bio-energy transport along protein molecules is performed by soliton movement caused by the dipole-dipole electric interactions between neighboring amino acid residues. As such, EMFs can affect the structure of protein molecules and change the properties of the bio-energy transported in living systems. This mechanism of biological effect from EMFs involves the amino acid residues in protein molecules. To study and reveal this mechanism, we simulated numerically the features of the movement of solitons along protein molecules with both a single chain and with three channels by using the Runge-Kutta method and Pang's soliton model under the action of EMFs with the strengths of 25,500, 51,000, 76,500, and 102,000 V/m in the single-chain protein, as well as 17,000, 25,500, and 34,000 V/m in the three-chain protein, respectively. Results indicate that electric fields (EFs) depress the binding energy of the soliton, decrease its amplitude, and change its wave form. Also, the soliton disperses at 102,000 V/m in a single-chain protein and at 25,500 and 34,000 V/m in three-chain proteins. These findings signify that the influence of EMFs on the bio-energy transport cannot be neglected; however, these variations depend on both the strength and the direction of the EF in the EMF. This direction influences the biological effects of EMF, which decrease with increases in the angle between the direction of the EF and that of the dipole moment of amino acid residues; however, randomness at the macroscopic level remains. Lastly, we experimentally confirm the existence of a soliton and the validity of our conclusion by using the infrared spectra of absorption of the collagens, which is activated by another type of EF. Thus, we can affirm that both the described mechanism and the corresponding theory are correct and that EMFs or EFs can influence the features of energy transport in living systems and thus have certain biological effects.