•n-Alkane concentration varied among different submerged plants.•Algal n-alkane concentration very low.•Aquatic plants contained high relative amount of long chain homologues.•Submerged plant ...n-alkane contribution to lacustrine sediments should be considered.•Algae contributed n-alkanes minimally to the lake sediments.
Long chain n-alkanes (C27–C33) in lake sediment records are commonly considered to be terrestrial plant biomarkers when reconstructing paleoclimatic and paleolimnological history. However, the extent to which their accumulation is influenced by n-alkanes originating from algae and submerged plants is largely unclear. Furthermore, to our knowledge, few studies have systematically analyzed the variation in n-alkane concentration or distributions between different submerged plant and algal species. We systematically investigated the n-alkane distributions of 13 algae (including 10 Cladophora and 3 Spirogyra), 68 submerged plants (including 37 Potamogeton, 7 Myriophyllum, 4 Ruppiaceae and 20 Chara) and 13 terrestrial plants (including 7 grasses and 6 shrubs) from 16 Qinghai-Tibetan Plateau lakes. The results indicate that the total n-alkane (C21–C33) concentration varied between different submerged plants. Potamogeton, Myriophyllum and Ruppiaceae exhibited high concentration, with average values 235.8, 295.9 and 275.9μg/g, respectively. These values were slightly higher than the concentrations found in terrestrial plant leaves (avg. 206.4μg/g), whereas the average concentration in Chara was only 2.0μg/g, significantly lower than that of other submerged plants. Similarly, the concentration in algae was also very low, with average values of 2.0μg/g and 4.0μg/g for Cladophora and Spirogyra, respectively. Submerged plant and algal long chain (C27–C33) alkanes accounted for a large proportion of the total C21–C33n-alkanes, with average ratios (long chain vs. total n-alkanes) of 20, 3, 22 and 27% for Potamogeton, Myriophyllum, Ruppiaceae and Chara, respectively. Cladophora and Spirogyra exhibited average ratios of 34% and 65%, respectively. Therefore, submerged plant long chain n-alkane contributions to lacustrine sediments, especially those of Potamogeton and Ruppiaceae, should not be considered negligible due to their high n-alkane concentration. Conversely, some algae, such as Cladophora and Spirogyra, minimally contributed n-alkanes to the lake sediments.
This paper proposes a four-plate compact capacitive coupler and its circuit model for large air-gap distance capacitive power transfer (CPT). The four plates are arranged vertically, instead of ...horizontally, to save space in the electric vehicle charging application. The two plates that are on the same side are placed close to each other to maintain a large coupling capacitance, and they are of different sizes to maintain the coupling between the primary and secondary sides. The circuit model of the coupler is presented, considering all six coupling capacitors. The LCL compensation topology is used to resonate with the coupler and provide high voltage on the plates to transfer high power. The circuit model of the coupler is simplified to design the parameters of the compensation circuit. Finite-element analysis is employed to simulate the coupling capacitance and design the dimensions of the coupler. The circuit performance is simulated in LTspice to design the specific parameter values. A prototype of the CPT system was designed and constructed with the proposed vertical plate structure. The prototype achieved an efficiency of 85.87% at 1.88-kW output power with a 150-mm air-gap distance.
This paper proposes a six-plate capacitive coupler for large air-gap capacitive power transfer to reduce electric field emissions to the surrounding environment. Compared to the conventional ...four-plate horizontal structure, the six-plate coupler contains two additional plates above and below the inner four-plate coupler to provide a shielding effect. Since there is a capacitive coupling between every two plates, the six-plate coupler results in a circuit model consisting of 15 coupling capacitors. This complex model is first simplified to an equivalent three-port circuit model, and then to a two-port circuit model which is used in circuit analysis and parameter design. This six-plate coupler can eliminate the external parallel capacitor in the previous LCLC topology, which results in the LCL compensation and reduces the system cost. Due to the symmetry of the coupler structure, the voltage between shielding plates is limited, which reduces electric field emissions. Finite element analysis by Maxwell is used to simulate the coupling capacitors and electric field distribution. Compared to the four-plate horizontal and vertical structures, the six-plate coupler can significantly reduce electric field emissions and expand the safety area from 0.9 to 0.1 m away from the coupler in the well-aligned case. A 1.97 kW prototype is implemented to validate the six-plate coupler, which achieves a power density of 1.95 kW/m 2 and a dc-dc efficiency of 91.6% at an air-gap of 150 mm. Experiments also show that the output power maintains 65% of the well-aligned value at 300 mm X misalignment, and 49% at 300 mm Y misalignment.
Approximately 90% of gas hydrates are buried in fine-grained sediments, especially in the South China Sea. The potential instability of fine-grained sediments induced by hydrate dissociation requires ...investigation of the shear strength and pore pressure response of sediments during hydrate recovery. To date, most studies have focused on the undrained mechanical behavior of gas hydrate–bearing sand or gas hydrate–free clay — few studies have examined gas hydrate–bearing fine-grained sediments. Because of the low-permeability and water-saturated characteristics of the sediments in the South China Sea, a series of undrained triaxial shear tests were performed on water-saturated methane hydrate-bearing clayey–silty sediments in this area. The experimental results show that the failure strength of methane hydrate–bearing sediments (MHBSs) increases with the increase in hydrate saturation and initial effective mean stress. The excess pore-water pressure of MHBSs remains positive during shear. Cohesion in the Mohr–Coulomb model increases with the increase in hydrate saturation, while the internal friction angle in the Mohr–Coulomb model has little dependence on the hydrate saturation.
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•A new theory named “crossover relaxor ferroelectrics” were reported.•Crossover relaxor 0.9BBNT-0.1SSN ceramic processes high Wrec of 2.02 J/cm3 and η of 90.18% at ...206 kV/cm.•0.9BBNT-0.1SSN ceramic exhibits strong chemical and electrical uniformity.•The excellent thermal stability, frequency stability, and cycle life stability have been achieved in 0.9BBNT-0.1SSN ceramic.
With a view to the rapid development of pulsed power capacitors, the demands for higher energy density, energy efficiency, and stability have increased significantly. A large amount of research has been devoted to the energy storage field of dielectric ceramics, however, scientific and effective strategy to design novel materials with excellent energy storage performance is still lacking. In this work, a new guideline was proposed that higher energy density and efficiency are easier obtained in crossover relaxor ferroelectrics, which is between normal ferroelectrics and relaxor ferroelectrics. Based on this theory, a series of lead-free (1-x)(0.65BaTiO3-0.35Bi0.5Na0.5TiO3)-xSr(Sc0.5Nb0.5)O3 ((1-x)BBNT-xSSN, x = 0, 0.05, 0.10, 0.15, 0.20) ceramics are designed and investigated. Optimal energy storage properties are achieved in 0.9BBNT-0.1SSN ceramic, with a large Wrec of 2.02 J/cm3 and a high η of 90.18% under a moderate electric field of 206 kV/cm. More importantly, both the Wrec and η of 0.9BBNT-0.1SSN ceramic show outstanding stability (including frequency, thermal, and cycle life stability) at 150 kV/cm, which is superior to other lead-free ceramics. These results demonstrate 0.9BBNT-0.1SSN ceramic is a promising candidate for practical energy storage applications.
•The doping of SSN increased the band gap width and decreased the grain size.•The ceramic possesses an energy density of 4.42 J/cm3 and an efficiency of 60%.•The transmittance of the ceramic is 76.7% ...and 84.5% at 780 and 1378 nm, respectively.•0.825KNN-0.175SSN ceramic exhibited a small strain effect of 0.022%.
Lead-free transparent ferroelectric ceramics with superior energy storage properties are highly desirable for pulsed power technologies and the increased optical transparency demand. However, the transparency and energy storage density of lead-free bulk ceramics cannot meet the requirements of their wide applications due to the coarse microstructure and relatively low breakdown strength. In this study, a design strategy is proposed to optimize the energy storage characteristics and transparency of ceramics by introducing nanodomains, increasing the band gap energy and reducing the grain size. The results showed that submicron grain (0.21 μm) and large band gap energy (Eg = 3.21 eV) were achieved through the introduction of the second component Sr(Sc0.5Nb0.5)O3 (SSN). An excellent transparency of up to 84.5% in the near-infrared region (1378 nm), a high energy density (W) of ~4.42 J·cm−3 and an extremely small strain of ~0.022% were simultaneously achieved in the 0.825(K0.5Na0.5)NbO3-0.175Sr(Sc0.5Nb0.5)O3 (0.825KNN-0.175SSN) ceramics. These results revealed the potential applications of (K0.5Na0.5)NbO3-based ceramics for energy storage and provide a feasible approach of domain engineering to develop new lead-free energy storagetransparency materials.
Although extensive studies have been done on lead-free dielectric ceramics to achieve excellent dielectric behaviors and good energy storage performance, the major problem of low energy density has ...not been solved so far. Here, we report on designing the crossover relaxor ferroelectrics (CRFE), a crossover region between the normal ferroelectrics and relaxor ferroelectrics, as a solution to overcome the low energy density. CRFE exhibits smaller free energy and lower defect density in the modified Landau theory, which helps to obtain ultrahigh energy density and efficiency. The (1–x)Ba0.65Sr0.35TiO3–xBi(Mg2/3Nb1/3)O3 ((1–x)BST–xBMN) (x = 0, 0.08, 0.1, 0.18, 0.2) ceramic was synthesized by a solid-state reaction method. The solid solutions exhibit dielectric frequency dispersion, which suggests typical relaxor characteristics with the increasing BMN content. The crossover ferroelectrics of 0.9BST–0.1BMN ceramic possesses a high energy storage efficiency (η) of 85.71%, a high energy storage density (W) of 3.90 J/cm3, and an ultrahigh recoverable energy storage density (W rec) of 3.34 J/cm3 under a dielectric breakdown strength of 400 kV/cm and is superior to other lead-free BaTiO3 (BT)-based energy storage ceramics. It also exhibits strong thermal stability in the temperature range from 25 to 150 °C under an electric field of 300 kV/cm, with the fluctuations below 3% and with the energy storage density and energy efficiency at about 2.8 J/cm3 and 82.93%, respectively. The enhanced recoverable energy density and breakdown strength of BT-based materials with significantly high energy efficiency make it a promising candidate to meet the wide requirements for high power applications.
Investigations and applications of renewable and sustainable energy have become central for addressing the issue of emissions of greenhouse gases from the use of fossil transportation fuels. ...Triglyceride-based liquid fuels have great potential as substitutes for petroleum and its derivatives. To date, the proven technologies for converting triglycerides into biofuels include transesterification, thermal cracking conversion, and hydrogenation. This paper presents an overview of recent research on these conversion technologies, employing homogeneous, heterogeneous, enzymatic, and photocatalytic catalysts. We focus on technical aspects critical to triglyceride conversion, including feedstock analysis, mechanism research, analysis of technological advantages and disadvantages, and catalyst development and selection. Biodiesel produced by the transesterification process must be blended with diesel before use due to its higher oxide content. The resultant “green diesel” has a broader range of applications, especially when its structure has been upgraded. Life cycle assessment (LCA) and greenhouse gas (GHG) emissions are reviewed to assess the renewability and sustainability of biofuels. We discuss the typical biodiesel production technologies with their development status, as well as the relevant policies and prospects for biofuels, mainly concerning biodiesel and aviation biofuel. It is hoped that our work will be of guiding significance for future biofuel research.
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•Overview of triglycerides biomass resources and their composition characteristics.•Overview of various possibilities conversion technologies for biofuel production are provided.•Overview of the composition characteristics of biodiesel and aviation biofuel and further upgraded for improving quality.•LCA and GHG emissions are reviewed to assess the renewability and sustainability of biofuels.
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