Larger Maximum Research Articles

Hydrothermal synthesis, characterization of Co3Sb4O6F6 and carbon doped Co3Sb4O6F6 and their application towards photocatalytic dye degradation, adsorption, catalytic Knoevenagel condensation and bacterial disinfection

Single crystals of Co3Sb4O6F6 have been grown by employing hydrothermal techniques. Table sugar was utilized to prepare carbon-doped Co3Sb4O6F6. The objective was to employ Co(II)-based metal oxyfluoride comprising a stereochemically active lone pair element (Sb3+) and its carbon-doped analogues for the multifunctional applications. The impact of carbon doping on Co3Sb4O6F6 has been evaluated towards the changes in photocatalytic, catalytic, and adsorbent efficiency. The changes in carbon percentage affect the physical and chemical properties of the host material. A larger percentage of carbon doping turns the photocatalytic ability of the host material into an adsorbent for the removal of dye. The single crystal X-ray diffraction study reveals that Co3Sb4O6F6 crystallizes into cubic symmetry. However, powder X-ray diffraction study reveals the structural transformation in the carbon-doped Co3Sb4O6F6. It also reduces the band gap energy of the host material, and 4 wt% C@Co3Sb4O6F6 turns out to be an efficient photocatalyst. Large-scale carbon doping (15 wt%) appears to be an effective strategy to increase the surface charge and BET surface area, as consequences adsorption property develops in 15 wt% C@Co3Sb4O6F6/H2O2 for the elimination of methylene blue (MB). This favourable chemical adsorption process occurs with large maximum adsorption capacity (qmax = 58.41169 mg g-1), as evident from the Langmuir adsorption isotherm. Scavenger experiment confirms that the photocatalytic activities of the as-synthesised compounds were triggered by the active participation of the hydroxyl radical (.OH). The catalytic efficiencies of both parent and doped compounds are also established for the solvent-free Knoevenagel condensation reaction with 90 % yield at moderate temperature. Bacterial disinfection studies by the ‘Disc diffusion method’ confirm that Co3Sb4O6F6 shows better efficiency than the carbon doped compound against both Gram-positive and Gram-negative bacteria.

Solution-Processed Pb(Zr,Ti)O3 Thin Films with Strong Remnant Pockels Coefficient.

In contrast to the widely studied electrical properties of Pb(Zr,Ti)O3 thin films, which have led to their applicability in various application areas such as thin film capacitors, microelectronics, and ferroelectric memories, the electro-optic (EO) properties are far less studied, which hinders the applicability of Pb(Zr,Ti)O3 films for EO applications such as heterogeneously integrated phase modulators in silicon (Si) photonics. Therefore, the EO properties of Pb(Zr,Ti)O3 films need to be further investigated to pave the way for the applicability of Pb(Zr,Ti)O3 films in EO applications. As the EO properties of ferroelectric thin films strongly depend on their crystal phase and texture, which in turn are influenced by the method of film fabrication. Therefore, in this work, we investigate the EO properties of a promising solution process using a La2O2CO3 template film. We successively characterize the precursor ink, microstructure and EO properties of the solution-processed Pb(Zr,Ti)O3film. The Pb(Zr,Ti)O3 film exhibits a fiber texture and has a large maximum and remnant Pockels coefficient (reff) of 69 pm V-1 and 66 pm V-1, respectively. The integration into a ring resonator-based modulator shows a VπL of 2.019 V cm. The determination of these promising EO properties could further pave the way for the applicability of Pb(Zr,Ti)O3 thin films in Si photonics.

Physical parameters and orbital evolution of asteroids in retrograde orbits

Context. We studied the dynamical orbital and physical evolution of all 21 numbered and 13 selected unnumbered asteroids in retrograde orbits. Aims. Based on all published observations of studied asteroids in retrograde orbits, we computed their starting orbital elements, absolute magnitudes, and diameters, together with the non-gravitational parameters A2 and da/dt. Methods. Using publicly available orbital computation methods, we studied the dynamical evolution of orbital elements and the physical parameters of asteroids: rotation period, spin direction, and the non-gravitational parameters A2. Results. Lyapunov times (LT) for studied asteroids are short, from 60 to 36 496 yr, with a mean of 5978. Without considering non-gravitational effects, LT is longer: values range from 328 to 63 165 yr, with a mean of 6392. Over the next 10 Myr and beyond, the rotation period of the studied asteroids P decreases by approximately 8%. Moreover, 15% of the clones slow down. Conclusions. The starting spin distribution becomes flatter, with only one large maximum in the range (0–5) deg containing 279 clones (i.e. approximately 13%). However, the non-gravitational parameter da/dt has a maximum value of around (0–0.04)× 10−5 au day−2 .

The Ramsey Numbers for Trees of Large Maximum Degree Versus the Wheel Graph W8\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$W_8$$\\end{document}

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Achieving high electromechanical response in lead-free BNT-BT ceramics through synergistic A/B-site doping

Lead-free Bi0.5Na0.5TiO3-based ceramics show great promise for achieving high unipolar strain. However, it remains challenging to implement an effective strategy for microstructural designs with high electromechanical response. Herein, a direct composition-engineering method based on A/B-sites doping is adopted to introduce a synergistic effect of reduced oxygen vacancies, lattice distortion, ferroelectric-to-relaxor phase transition, and nano-sized domains, resulting in a high piezoelectric strain coefficient d*33 of 857 pm/V at a small electric field of 4 kV/mm. Furthermore, a large room-temperature maximum polarization (Pm) of 72.4 μC/cm2 was observed at high electric field. A phase transition from coexisting rhombohedral–tetragonal to pseudocubic was engineered by finely tuning the contents of NaTaO3, leading to a decrease in both remnant polarization (Pr) and coercive field (Ec). The phase diagram of 1-x[0.935(Bi0.5Na0.5TiO3)-0.065(BaTi0.99Nb0.01O3)]-x(NaTaO3) (x = 0–0.04) is proposed, providing a roadmap for engineering high-performance piezoelectric ceramics with enhanced electrostrain responses, which may find potential applications as piezoelectric actuators.

Mechanical and thermal performances of multistage flexible thermal control device: A case study in cylindrical heat pipe

Multistage flexible heat pipe has been proved to offer advantage of large flexibility as well as low thermal resistance. However, the effects of structural parameters on the comprehensive performances of such multistage thermal control device are still unclear, particularly regarding their mechanical properties. In this paper, effect of structural parameters on the mechanical and thermal performances of bionic multistage heat pipe is investigated. Results show that the stiffness of polymer tubes primarily determines the flexibility of multistage flexible heat pipe. The heat pipe with 4 metal tubes in the adiabatic section can achieve relative large flexibility and maximum bending angle as well as the short start-up time. The bending rigidity of multistage flexible heat pipe increases from 97624.4 N mm2 to 293152.9 N mm2 when its metal ratio raises from 0 % to 80 %. The thermal resistance of multistage flexible heat pipe decreases more than 32.9 % compared to the traditional flexible heat pipe. When the flexible heat pipe remains straight, the heat transfer performance will slightly increase as the shell metal ratio increases. However, its thermal resistance will also have an additional increase when bending. These results can serve as a guide for the design of the multistage flexible thermal control device.

Nanoscale assembly of MoS2/CoS2/Ni3S2 grown on Ni foam for synergistic capture of iodine

We report a series of MoS2/CoS2/Ni3S2/NF heterogeneous interfaces with multiple types of adsorption sites, which exhibit excellent iodine capture performance. The optimized MoS2/CoS2/Ni3S2/NF-13 obtained at Mo:Co molar ratio of 1:3 shows an extremely large maximum iodine capture of 1804 mg/g. For the including component of Ni3S2/NF, REDOX reaction between Ni0/S2- and I2 offers the main driving force of chemisorption toward iodine (forming NiI2 and S8), while for MoS2, the electrostatic adsorption makes the main contribution to the iodine capture, and for CoS2, interfacial interactions promote the uptake capability of iodine. We perform density functional theory (DFT) calculations to determine the iodine adsorption energies (Ead), which show that in Ni3S2 the Ni and S both serve as iodine sorption sites and Ni site binds more tightly to I2 than S site does, while for MoS2, the S site (rather than Mo) prefers to adsorb the I2. X-ray absorption fine structures (XAFS) indicate that after iodine capture, oxidation states of Mo and Ni are increased more than that of Co, verifying Ni3S2 and MoS2 interact more than CoS2 on I2. Though CoS2 component does not directly adsorb I2, interfacial electron transfers of Co → Ni and Co → Mo significantly promote iodine sorption capability. Synergistic effect of the multiple components/sites in the MoS2/CoS2/Ni3S2/NF assembly offers the wonderful iodine capture. This work provides a novel perspective and theoretical reference for tailoring effective metal sulfides-based sorbents to trap iodine from radioactive wastes.

Characteristics of pebble shape and the amount of pebble abrasion measured with a replica reproduced on a curling rink

The shape of pebbles on a curling rink was measured using a replica of the ice surface of the rink to understand the characteristics of pebbles after being in contact with stones. We focused on pebbles with flat tops for which the average shape was 3.81 mm in diameter at the lower base, 1.16 mm in diameter at the upper surface, 0.12 mm in maximum height, and 5.4° in contact angle. A scratch of about 1 µm in depth and 40 µm in width (traces of pebbles cut by a running band at the bottom of the stone) was observed on the upper surface. The pebbles were also found to have a moderate lower base diameter that preferentially contacted the nipper or stone due to its large maximum height value immediately after formation. Experiments to determine the amount of pebble abrasion associated with the passing of stones revealed that the average height of their upper surface decreased by 1 µm and the area of the upper surface increased by 0.21 mm2 for each stone passing as the stone cut the pebbles.

Abstract 3024: Mitochondrial Volume Abnormalities In Gastrocnemius Muscle Of Patients With Peripheral Artery Disease

Background: The mechanisms of claudication in patients with peripheral artery disease (PAD) are poorly understood. Mitochondria are responsible for ATP production during aerobic conditions but may become structurally impaired in patients with chronic ischemia and PAD. Research Question: Are mitochondrial volumes different in patients with PAD compared with age-matched controls? Aims: To better understand mitochondrial abnormalities and ultrastructure in patients with PAD. Methods/Approach: Patients with PAD (defined as ABI <0.85) and age-matched controls (ABI 1.00-1.40) were recruited and underwent gastrocnemius muscle biopsy. Muscle samples were collected in optimal cutting temperature compound. Mitochondria were labeled with cytochrome oxidase IV antibody and Cy3 fluorescence secondary antibody and images were rendered in three dimensions using structured illumination microscopy to quantify mitochondrial size, content, and morphology. Comparisons were done with a Mann-Whitney U test. Results/Data: Forty-eight subjects (median [IQR] age 66.5 [59.0, 74.0] years, 32 (66.7%) male) were recruited and underwent gastrocnemius muscle biopsy, including 16 controls and 32 with PAD. The largest singular mitochondrial volume was greater in those with PAD (22.6 vs. 4.2μm 3 , p=0.01, Figure 1A) but the median mitochondrial volume was smaller (0.07 vs. 0.01μm 3 , p=0.03, Figure 1B). While no control mitochondria were larger than 7.2μm 3 , 1% of mitochondria in patients with PAD were larger than 10μm 3 (Figure 1C). There was no difference in the total mitochondrial volume or content between PAD and controls. Conclusion: Patients with PAD have larger maximum but smaller median mitochondria sizes in the gastrocnemius muscle, suggesting greater heterogeneity of mitochondrial size in those with PAD. The changes in mitochondrial morphology may result in mitochondrial inefficiency and an impaired compensatory response in the setting of chronic ischemia from PAD.

High energy storage performance induced by the introduction of BiScO3 into (Bi0.5Na0.5)TiO3–BaTiO3 lead-free ferroelectric ceramics

In this work, ternary 0.25(Bi0.5Na0.5)TiO3-(0.75-x)BaTiO3-xBiScO3(abbreviated as 0.25BNT-(0.75-x)BT-xBS, x = 0.19, 0.21, 0.23, 0.25, 0.27) lead-free ferroelectric ceramics were synthesized using the solid-state reaction method. The introduction of BiScO3 into (Bi0.5Na0.5)TiO3–BaTiO3 ceramics had a significant impact on changing the phase structures, and microstructures, as well as the dielectric and ferroelectric properties. All ceramics exhibited a coexistence of tetragonal(P4bm) and rhombohedral(R3c) perovskite phases, while the influence of the BiScO3(BS) content on the average grain size was not significant. Slim polarization-electric field hysteresis loops were recorded for the 0.25BNT-(0.75-x)BT-xBS ceramics, with low remnant polarization (Pr) and large maximum polarization(Pmax). 0.25BNT-0.50BT-0.25BS ceramic had the largest Pmax, which induced a high energy storage density of 2.93 J/cm3 and energy storage efficiency of 91 % under a low electric field of 230 kV/cm 0.25BNT-0.50BT-0.25BS ceramic not only yielded excellent fatigue resistance, but also maintained good energy storage performance at high temperature and high frequency, which are considered of great importance since they can be leveraged for the potential development of high temperature and frequency capacitors. In addition, an excellent pulse performance was measured, with a high discharge energy density of 3.42 J/cm3 and a fast discharging rate t0.9 of 130 ns. This good pulse performance was maintained at high temperatures, suggesting that the proposed material is also highly competitive for applications where high-temperature pulse devices are required.

Toward Design Rules for Multilayer Ferroelectric Energy Storage Capacitors - A Study Based on Lead-Free and Relaxor-Ferroelectric/Paraelectric Multilayer Devices.

Future pulsed-power electronic systems based on dielectric capacitors require the use of environment-friendly materials with high energy-storage performance that can operate efficiently and reliably in harsh environments. Here, a study of multilayer structures, combining paraelectric-like Ba0.6Sr0.4TiO3 (BST) with relaxor-ferroelectric BaZr0.4Ti0.6O3 (BZT) layers on SrTiO3-buffered Si substrates, with the goal to optimize the high energy-storage performance is presented. The energy-storage properties of various stackings are investigated and an extremely large maximum recoverable energy storage density of ≈165.6Jcm-3 (energy efficiency≈93%) is achieved for unipolar charging-discharging of a 25-nm-BZT/20-nm-BST/910-nm-BZT/20-nm-BST/25-nm-BZT multilayer structure, due to the extremely large breakdown field of 7.5MVcm-1 and the lack of polarization saturation at high fields in this device. Strong indications are found that the breakdown field of the devices is determined by the outer layers of the multilayer stack and can be increased by improving the quality of these layers. Authors are also able to deduce design optimization rules for this material combination, which can be to a large extend justify by structural analysis. These rules are expected also to be useful for optimizing other multilayer systems and are therefore very relevant for further increasing the energy storage density of capacitors.

Metavalent Bonding in Cubic SnSe Alloys Improves Thermoelectric Properties over a Broad Temperature Range

AbstractMonocrystalline SnSe is one of the most promising thermoelectric materials with outstanding performance and a high abundance of constituting elements. However, polycrystalline SnSe, which is more robust for applications, only shows large figure‐of‐merit (zT) values in its high‐symmetry phase. Stabilizing the high‐symmetry phase at low temperatures can thus enhance the average zT value over a broad temperature range. In this work, the high‐symmetry rock‐salt SnSe phase is successfully obtained by alloying SnSe with AgVVI2 compounds (V = Sb, Bi; VI = Se, Te). These cubic SnSe phases show a unique portfolio of properties including a high optical dielectric constant, a large maximum of optical absorption, a large Born effective charge, and abnormal bond‐breaking behavior in laser‐assisted atom probe tomography. All of these characteristics are indicative of metavalent bonding. In contrast, the Pnma phase of SnSe employs covalent bonding. The enhanced symmetry at low temperatures is realized by tailoring chemical bonding. Concomitantly, zT near room temperature is increased by a factor of more than 10 from the pristine Pnma SnSe to Fmm SnSe alloys. This provides insights into the enhancement of the thermoelectric performance of SnSe and other chalcogenides over a broad temperature range by manipulating the chemical bonds.

Optimization design of shearer drum height adjusting mechanism based on particle swarm optimization algorithm

The underground working environment of the shearer is complex and the working conditions are relatively poor. It is necessary to continuously adjust the height of the rocker arm during the operation, improve the operation efficiency, and improve the ability of the shearer to adapt to the more complex coal seam working environment. In order to optimize the structure of the shearer adjustment mechanism, the strength and strength of the adjustment mechanism are improved by increasing the size and angle of the adjustment mechanism and reducing the size and angle. Therefore, an optimized particle group design method is proposed to optimize the drum adjustment mechanism of the shearer. Seven parameters such as large lever, small lever and maximum swing angle are selected as design variables. Under the condition of limiting mining height and rocker length, an optimization model with rolling angle and cylinder stress as objective functions is established. The working characteristics of each part of the coal machine height adjustment mechanism are analyzed. The particle swarm optimization algorithm is used to optimize the key parameters, and the optimization results are verified to ensure their accuracy. The optimization results are compared with the original parameters. The results show that compared with the pre-optimization, the cylinder stroke is shortened by 17.9%, the cylinder length is shortened by 8.94%, the rolling angle is reduced by 2.83%, the cylinder tension is reduced by 12.1%, and the rocker bending moment is increased by 6.83 %, which meets the original design goal. Therefore, the research provides a reference for the optimal design of the coal machine height adjustment system.

Disclosing the dependencies of ferroelectric and piezoelectric performances on crystalline states of P(VDF‐TrFE) films by molecular dynamics simulations

AbstractWe present a molecular dynamics simulation method including x‐ray diffractometer pattern calculation, mean square displacement (MSD), and nonbonding energy distribution (NED) to disclose the dependencies of condensed structure on its crystalline process of the poly(vinylidene fluoride‐trifluoroethylene) (P(VDF‐TrFE)) films. For comparison, the P(VDF‐TrFE) solution is casted into the films, and followed that different thermal processes are performed to fabricate the crystalline states of the films. Simulation and experimental results have good consistency, indicating that high temperature annealing can effectively promote all‐trans β phase in the crystal region of P(VDF‐TrFE). As such, P(VDF‐TrFE) 80/20 mol% annealing at 140°C shows a higher MSD (~27.5 Å2) and a faster reducing rate of NED than that of other films, contributing to a large maximum polarization (Ps) of ~15.5 μC cm−2, high a remnant polarization (Pr) of ~11.8 μC cm−2, and an attractive piezoelectric strain coefficient (d33) of −27.1 pC N−1 under 200 MV m−1, respectively, and providing a reference for the applications of P(VDF‐TrFE) in flexible sensors, actuators, transducers, and so forth.

Fast peak error correction algorithms for proteoform identification using top-down tandem mass spectra.

Proteoform identification is an important problem in proteomics. The main task is to find a modified protein that best fits the input spectrum. To overcome the combinatorial explosion of possible proteoforms, the proteoform mass graph and spectrum mass graph are used to represent the protein database and the spectrum, respectively. The problem becomes finding an optimal alignment between the proteoform mass graph and the spectrum mass graph. Peak error correction is an important issue for computing an optimal alignment between the two input mass graphs. We propose a faster algorithm for the error correction alignment of spectrum mass graph and proteoform mass graph problem and produce a program package TopMGFast. The newly designed algorithms require less space and running time so that we are able to compute global optimal alignments for the two input mass graphs in a reasonable time. For the local alignment version, experiments show that the running time of the new algorithm is reduced by 2.5 times. For the global alignment version, experiments show that the maximum mass errors between any pair of matched nodes in the alignments obtained by our method are within a small range as designed, while the alignments produced by the state-of-the-art method, TopMG, have very large maximum mass errors for many cases. The obtained alignment sizes are roughly the same for both TopMG and TopMGFast. Of course, TopMGFast needs more running time than TopMG. Therefore, our new algorithm can obtain more reliable global alignments within a reasonable time. This is the first time that global optimal error correction alignments can be obtained using real datasets. The source code of the algorithm is available at https://github.com/Zeirdo/TopMGFast.

An auxiliary optimization method for electric heating renovation based on using a clustering algorithm

The large amount of pollutants emitted by coal heating in winter is one of the main causes of haze, which brings great trouble to people’s lives. To reduce air pollution caused by coal burning and improve air quality, the state advocates the transformation of traditional electric heating methods to accelerate the transformation of China’s energy system to a clean and low-carbon model and improve the utilization rate of renewable energy in China. Therefore, this article through the calculation of the residual capacity of the retrofit and the calculation of the air conditioning load to assist the electric heating transformation. Firstly, the average power of the transformer during a high power period is calculated instead of taking the maximum power directly, which solves the problem of small residual capacity caused by a large maximum load rate and maximizes the transformable capacity. Secondly, the cluster analysis of air conditioning heating as one of the typical electric heating methods is carried out by the K-means clustering method, and the air conditioning load is obtained as the data reference during the electric heating transformation to assist the optimization transformation of electric heating. The two methods are further studied and verified by two examples, and the theory guides the practice to assist the electric heating transformation and achieve the goal of energy saving and emission reduction.

Enhanced energy storage and temperature-stable dielectric properties in (1-x)[(Na0.4K0.1Bi0.5)0.94Ba0.06TiO3]-xLa0.2Sr0.7TiO3 lead-free relaxor ceramics

With the continuous growth in sustainable and renewable technologies, ceramic capacitors are emerging as a promising energy storage device. Lead-free (1-x)[(Na0.4K0.1Bi0.5)0.94Ba0.06TiO3]-xLa0.2Sr0.7TiO3 (0 ≤ x ≤ 0.40) ceramics were prepared using the solid-state reaction technique for obtaining relaxor characteristics with improved energy storage density, efficiency, and temperature stability of dielectric permittivity. A high recoverable energy density (Wr) ∼ 2.39 J/cm3 with a good efficiency (η) of ∼ 75.21% was obtained for x = 0.30 composition under 220 kV/cm applied field. The specimen x = 0.30 exhibited excellent fatigue resistance during 105 cycles and good temperature stability of energy storage characteristics (Wr > 0.87 J/cm3, η > 74%) in the temperature range of 25–180 °C under 100 kV/cm. In addition, the temperature range in which the dielectric permittivity variation was less than ±15% was very wide (204 °C (63–267 °C) and 275 °C (39–314 °C) for x = 0.30 and 0.20 specimens, respectively). Significant improvements in material performance were attributed to A-site engineering, which resulted in a mixture of P4bm and R3c polar nano regions (PNRs), leading to reduced hysteresis loss and temperature-stable dielectric permittivity. Additionally, the size of PNRs ranged between 3 and 6 nm, with the P4bm phase dominating in the x = 0.30 specimen, leading to a large maximum polarization under an applied electric field. Therefore, (1-x)[(Na0.4K0.1Bi0.5)0.94Ba0.06TiO3]-xLa0.2Sr0.7TiO3 relaxor ceramics are promising for high energy density materials and electronic applications requiring high permittivity stability over a wide temperature range.

Tephra segregation profiles based on disdrometer observations and tephra dispersal modeling: Vulcanian eruptions of Sakurajima volcano, Japan

The profile of tephra concentration along a volcanic plume (i.e., the tephra segregation profile) is an important source parameter for the simulation of tephra transport and deposition and thus for the tephra sedimentation load. The most commonly-used approach is to treat an eruption as a single event (i.e., with a time-averaged mass eruption rate; MER). In this case, it is common to use pre-determined profiles that feature most of the tephra segregate at the top of the plume. However, case studies based on observations have revealed that large concentration maxima also appear at the lower part of the plume. To investigate this discrepancy, the impact of plume height on the temporal variations in the MER is examined. To this end, we use the tephra transport and dispersion model Tephra4D with MER estimates obtained from geophysical monitoring and maximum plume height observations to calculate the spatial distribution of the tephra deposit load for 39 eruptive events that consisted of explosions and quasi-steady particle emission from the Sakurajima volcano, Japan. A comparison of the model results with observations from a disdrometer network revealed that for both kinds of activity, maxima in tephra segregation can occur at heights below the reported plume height. The tephra segregation profiles of Vulcanian eruptions at Sakurajima volcano are consistent with most of the modeling studies giving profiles that feature most of the tephra segregating at the top of the plume if the temporal variation of the MER is taken into consideration to properly represent the total series of eruptive events in a sequence. This highlights that even though the activity at Sakurajima volcano is commonly characterized simply as Vulcanian eruptions, in addition to the primary plume developed due to the initial instantaneous release caused by the explosion, the subsequent continuous plume that can accompany the eruption plays an important role in particle emission. Calculations could not reproduce the simultaneous deposition of particles with a wide range of settling velocities in observations, suggesting the importance of volcanic ash fingers caused by gravitational instability in tephra transport simulations.Graphical

Complete signed graphs with largest maximum or smallest minimum eigenvalue

In this paper, we deal with extremal eigenvalues of the adjacency matrices of complete signed graphs. The complete signed graphs with maximal index (i.e. the largest eigenvalue) with n vertices and m≤⌊n2/4⌋ negative edges have been already determined. We address the remaining case by characterizing those with m>⌊n2/4⌋ negative edges. We also identify the unique signed graph with maximal index among complete signed graphs whose negative edges induce a tree of diameter at least d for any given d. This extends a recent result by Li, Lin, and Meng [Discrete Math. 346 (2023), 113250] who established the same result for d=2. Finally, we prove that the smallest minimum eigenvalue of complete signed graphs with n vertices whose negative edges induce a tree is −n2−1−1+O(1n).

Improved dielectric temperature stability and energy storage properties of BNT-BKT-based lead-free ceramics

The lead-free ceramics (1-x)(0.84Bi0.5Na0.5TiO3-0.16Bi0.5K0.5TiO3)-xBiMg2/3Nb1/3O3 (denoted as (1-x)BNKT-xBMN) and (1-y)(0.85BNKT-0.15BMN)-ySr0.7La0.2TiO3 with y = 0.3 (denoted as BNKMN-0.3SLT) were prepared by means of a conventional solid state sintering method. Effects of introduction of BiMg2/3Ni1/3O3 and Sr0.7La0.2TiO3 on phase structure, microstructure, and dielectric, ferroelectric and energy storage properties of the ceramics were studied in detail. The ceramics (1-x)BNKT-xBMN show pure perovskite structure, while BNKMN-0.3SLT appears a secondary phase. All ceramics exhibit dense microstructures with mean grain sizes between 0.56 μm and 1.36 μm. The introduction of SLT into BNKMN causes obvious decrease in dielectric constant around Curie temperature, inducing the widest temperature window of 263 °C from 29 °C to 292 °C for TCC≤±15 %. The ceramic BNKMN-0.3SLT shows high electric breakdown strength (Eb ∼ 300 kV/cm), large maximum polarization (Pm ∼ 36.48 μC/cm2), and low remanent polarization (Pr ∼ 1.70 μC/cm2), inducing high energy storage density of 4.03 J/cm3 as well as high energy storage efficiency of 85.2 %.