Constant Density Research Articles

The mechanical and microstructural behavior of heat treated, texture-controlled Ti-10%Mo alloys manufactured by laser powder bed fusion

The crystallographic texture of additively manufactured metals can change significantly depending on process parameters, which in turn affects mechanical performance. Titanium with 10 wt% molybdenum (Ti-10Mo) displays a significant oriented-to-misoriented transition (OMT) when laser scan speed is increased from 500 mm/s to 2000 mm/s at a constant volumetric energy density of 130 J/mm3. This alloy showed no significant ductility as-printed or when solution treated and air quenched due to ω nanoprecipitates and α’’ martensite but had an elongation to failure of 14.3% when heat treated for 3 h at 700 °C into a duplex α+β microstructure. Comparison of heat treated oriented, semi-oriented, and misoriented microstructures showed an increase in yield strength isotropy but a decrease in strength hardening rate isotropy with decreasing texture. Tensile plastic deformation was found to occur preferentially in the β-phase along the close packed {110} slip system, but also in the α-phase via the pyramidal slip system. Decreasing texture suppressed grain rotation towards these slip systems, leading to greater strain hardening. Fracture was shown to occur at the α-β interfaces, particularly at grain boundary nucleated α grains.

Experimental study on efficiency improvement methods of vanadium redox flow battery for large-scale energy storage

All-vanadium redox flow battery (VRFB) is a promising large-scale and long-term energy storage technology. However, the actual efficiency of the battery is much lower than the theoretical efficiency, primarily because of the self-discharge reaction caused by vanadium ion crossover, hydrogen and oxygen evolution side reactions, vanadium metal precipitation and other operational factors. Based on the above analysis, this paper proposes effective strategies and methods for improving the efficiency of the VRFB. The experimental results indicate that the voltage efficiency and system efficiency increased by 1.86% and 0.48%, respectively, when constant flow rate and variable current density charge/discharge methods are used. Meanwhile, when variable flow rate and current density charge/discharge methods are employed, the energy efficiency and system efficiency increased by 9.07% and 8.34%, respectively, resulting in significant improvement in energy storage capacity. The experiment has verified that this method can improve the efficiency and performance of VRFB, and can promote the development of VRFB.

Isotacticity in chiral phononic crystals for low-frequency bandgap

Realizing a low-frequency and broad bandgap is extremely challenging because the lattice constant, equivalent stiffness, and equivalent density must be taken into account in practice. Despite the advances of inertial amplification which is one of the ideal strategies to address this issue, the design ideas are mainly limited to the classic geometries featured by mirror symmetry (syndiotacticity), confining then progress in this topic. Here, we report numerical and experimental investigation of a chiral phononic crystal without mirror symmetry (isotacticity) according to the analogous Thomson scattering. Numerical analysis shows that due to the lack of one degree of freedom in isotactic lattice (ISL) compared to syndiotactic lattice (SYL), the bandgap starting-frequency of the ISL is significantly lower than that the one of the SYL by up to 66%. The bandgap properties are further demonstrated by simulation and experimental measurements. This research reveals that the condition of having alternating arrangement orientations between neighboring atoms is not indispensable for this kind of bandgap, and a rational geometry satisfying the Thomson scattering-based bandgap conditions can further reduce the bandgap frequency without affecting the stiffness and lightweight of the structure.

Mitigating silica fouling in electro-electrodialysis: Anode compartment modification and process intensification approaches

Electro-electrodialysis (EED) based causticization of industrial (agro-based paper mills) green liquor experiences severe silicate fouling issues (especially in anode compartment) resulting frequent shutdown, dismantling, cleaning and reassembling challenges. Therefore, continuous causticization through EED process becomes difficult. Appropriate design modification of the anode compartment along with periodic silica removal could overcome frequent shutdown issues, and execution of EED process for longer duration. The novel mechanism of silicon removal using EED process by the precipitant is also presented. Their treatment performances in removing silicon were statistically evaluated and confirmed by instrumental techniques. Using modified design and 200 cm2 of membrane area, 500 mL of 2.56 mol·L−1 of NaOH (92% Na+ ion recovery) could be produced in 4 h by electrolyzing 500 mL of industrial green liquor under constant current density, 60 mA·cm−2. Proposed modification could result ∼21% improvement in caustic recovery/energy consumption compared to unmodified anode compartment. With improve the performance which is the average current efficiency 74.5% and energy consumption 4.42 kWh·kg−1, was recorded.

Preparation and electrochemical performance of FG/SnS2 composite as a cathode material for high power thermal batteries

SnS2 is a promising cathode material for its high specific capacity (1232 mAh/g), but it’s limited to the low decomposition temperature and conductivity as the thermal battery application. Herein, the flaky graphite(FG) coating SnS2 composite (denoted as FG/SnS2) with excellent thermal stability and conductivity was prepared. Then, as a thermal battery cathode material, it presented longer working time at current constant density of 100 mA/cm2, and higher pulse voltage at 2A/cm2 pulse current density than the pure SnS2. Application as the engineering unit thermal battery, its performance of higher working voltage, lower total resistance, and more stable output capacity indicated it can be used for high-power thermal batteries.

Numerical Simulation of Flashing Flows in a Converging–Diverging Nozzle with Interfacial Area Transport Equation

Flashing flows of initially sub-cooled water in a converging–diverging nozzle is investigated numerically in the framework of the two-fluid model (TFM). The thermal non-equilibrium effect of phase change is considered by an interfacial heat transfer model, while the pressure jump across the interface is ignored. The bubble size distribution induced by nucleation, bubble growth/shrinkage, coalescence, and breakup is described based on the interfacial area transport equation (IATE) and constant bubble number density model (CBND), respectively. The results are compared with the experimental data. Satisfactory prediction of the axial pressure distribution along the nozzle as well as the flashing inception, is achieved by the TFM-IATE coupling method. It was also found that the vapor production in the diverging section was overpredicted, and the radial gas volume fraction distribution deviated from the experiment. The radial diameter profiles exhibit opposite patterns at the nozzle throat and near the outlet, and similar trends can be observed for the superheated degree. A poly-disperse method is suggested to be introduced to describe the evolution of interfacial area concentration.

A. Chemistry Corrosion potential of reinforced EDTA Zn-Fe Alloy in Acidic and Basic medium.

The manuscript presented the successfully synthesis of Zn-Fe alloy thin film deposition in sulfate bath on mild steel substrate. The hexadanted ligand EDTA was incorporated in alloy solution as corrosion inhibitor. All depositions were conducted at constant current density 2 mA/cm2 for 40 min. The morphological characterization of the thin film was analyzed with X-ray diffraction analysis (XRD) and Confocal laser microscopy. The Tafel polarization experiment was performed to determine the anticorrosion behavior of thin film in 3.5% NaCl and 0.1 M HCl solutions. The corresponding maximum corrosion efficiency of reinforced EDTA alloy is 93.57 and 94.02% in 3.5% NaCl and 0.1 M HCl solutions respectively.

Fluorinated poly(p-triphenyl piperidine) anion exchange membranes with robust dimensional stability for fuel cells

Anion exchange membrane fuel cells (AEMFCs), which are more economical than proton exchange membrane fuel cells (PEMFCs), stand out in the context of the rapid development of renewable energy. Superacid-catalyzed ether-free aromatic polymers have recently received a lot of attention due to their exceptional performance, but their development has been hampered by the trade-off between the dimensional stability and ionic conductivity of anion exchange membranes (AEMs). Here, we introduced fluoroketones containing different numbers of fluorinated groups (x = 0, 3 and 6) in the main chain of p-terphenyl piperidine because of the favorable hydrophobic properties of fluorinated groups. The results show that fluorinated AEMs can enhance OH− conductivity by building more aggregated hydrophilic channels while ensuring dimensional stability. The PTF6-QAPTP AEM with more fluorinated groups has the most excellent performance at 80 °C with an OH− conductivity of 142.7 mS cm−1 and a swelling ratio (SR) of only 4.55 %. Additionally, it exhibits good alkali durability, with the OH− conductivity and quaternary ammonium (QA) cation retaining at 93.45% and 92.6%, respectively, after immersion in a 2 M NaOH solution at 80 °C for 1200 h. In addition, the power density of the PTF6-QAPTP based single cell reaches 849 mW cm−2 when the current density is 1600 mA cm−2. The PTF6-QAPTP based cell has a voltage retention of 88% after 80 h of stability testing at a constant current density of 300 mA cm−2 at 80 °C.

E72 Distribution of cells and extracellular matrix in the marginal synovium during the postnatal period

Abstract Introduction The marginal transitional zone of the joint is of fundamental importance in joint pathology. The normal marginal synovium takes part in articular cartilage repair (Adachi et al. 2012). The inflamed marginal synovium, in turn, promotes irreversible damage to the adjacent cartilage and bone (Hitchon & El-Gabalawy, 2011). Early erosive damage in rheumatoid arthritis and osteophyte formation in osteoarthritis occurs primarily here (Allard et al. 1990). Objectives The morphology of the marginal synovium from birth till the 90th day was studied using the hip joints of Wistar rats. Methods The collection of joints was carried out on the first, seventh, 14th, 30th, 45th, 60th and 90th day (six rats in each group, 42 in total). Joints were fixed, decalcified and dehydrated. Histologic paraffine sections were stained with Mallory's trichrome and Hart's elastin staining, analyzed at the acetabular labrum by light microscopy (χ100), morphometrical and statistical (P < 0.05) methods with extrapolation to humans (Sengupta, 2013). The obtained data were presented as percentages. Results In the marginal synovium, cells and components of the extracellular matrix, which are typical for fibrous connective tissue, could be seen. The synovial lining cells are embedded in the modified basement membrane which includes collagen and elastic fibers. They form a three-dimensional reticulum in it and adjacent synovial subintima. Vessels of the microcirculatory bed are also widely represented in the marginal synovium. The overall quantity of collagen fibers increased gradually, exceeding on the 90th day (approximately corresponds to 18–19 human years) that of newborns by one and a half times (48.92 ± 3.39 vs 72.17 ± 7.77; P = 0.023). The number of arranged collagen fibers increased gradually, exceeding on the 90th day that of newborns almost twofold (37.25 ± 3.21 vs 60.08 ± 5.99; P = 0.008). The area of distribution of disarranged collagen fibers in newborns was almost four and a half times less than the overall quantity of collagen fibers (11.67 ± 1.03 vs 48.92 ± 3.39; P < 0.001) and did not change substantially throughout the experiment. The number of elastic fibers increased till the 30th day (0.63 ± 0.11 vs 18.3 ± 1.25; P < 0.001) and did not undergo significant changes later. In newborns, the area of distribution of ground substance was not considerably higher than the ratio of disarranged collagen fibers (10.42 ± 1.8 vs 11.67 ± 1.03; P = 0.562) and did not undergo substantial changes later. The distribution density of vessels increased till the 30th-45th day (4.5 ± 0.67 vs 7.5 ± 0.82 and 7.7 ± 0.54; P < 0.001; approximately corresponds to the 9th and 14th human years respectively), followed by a gradual decrease from the 60th day (7.05 ± 0.72; roughly corresponds to the 16th human years). The maximum number of cells was in newborns. Subsequently, it gradually decreased and was almost three times less on the 90th day than that of newborns (38.01 ± 3.06 vs 12.58 ± 1.53; P < 0.001). Conclusion The morphogenesis of the marginal synovium during the postnatal period is accompanied by a gradual decrease in the number of cells, an increase in the area occupied by elastic and arranged collagen fibers with a relatively constant distribution density of disarranged collagen fibers and ground substance together with an undulatory pattern in the distribution of vessels. These peculiarities emphasize the morphological uniqueness of the marginal transitional zone, which forms the innate nonspecific barrier between the joint capsule and the articular cartilage, and thereby provides the necessary anatomical and physiological integrity of the joint as a whole organ. Knowledge about the patterns of morphogenesis of the marginal synovium will help in the future to analyze the modeled pathological or boundary states in it. Ethics The study was approved by the ethics committee of the Zaporizhzhia State Medical University.

Evaluation of rhyolite rock as thermocline storage material for medium and high temperature applications

Nowadays, the packed bed filled with aggregates, which replaces a large part of the used fluid and prevents convective mixing in the storage liquid, has a better cost/storage time ratio. It is easily integrated with some types of renewable energy. Besides, it is cheap and more efficient without environmental impact. As a result, it was crucial to check some criteria to select the storage materials. In this regard, this paper aims to examine the properties of the rhyolite rock as a candidate for heat storage. It was collected from Oued Tensift near Marrakech, Morocco. The optimal temperature range for this rock was defined. Chemical and structural composition and thermo-physical properties of the rock are carried out by using XRF, EDX, DRX and TGA-DTA. Experimental heating and cooling tests were also performed at two different temperatures 300 °C and 600 °C to determine the effect of thermal cycling on the mineralogical structure of rhyolite rock. The found results indicate that this material can be used to store thermal energy for medium temperature (100–300 °C) as well as for high-temperature applications (below 650 °C) such as CSP plants.Rhyolite is a good candidate for heat storage as it exhibits structural stability even after undergoing thermal cycling. This stability means that the thermophysical and chemical properties required for heat storage can be maintained. When heated to 1000 °C, rhyolite undergoes minimal mass loss, which doesn’t exceed 1.5 %. This characteristic confirms its suitability for heat storage applications. Rhyolite has an almost constant bulk density (decrease around 0.18 kg/ m3) over a temperature of 600 °C, rhyolite's average capacity and thermal conductivity values are 1.92 MJ/m3. °C and 2.16 W/m.°C, respectively, when heated from ambient temperature to 400 °C. These values indicate the rock's ability to store and release heat efficiently.

E71 Distribution of cells and extracellular matrix in the normal marginal synovium of the hip joint capsule during the postnatal period

Abstract Introduction The marginal transitional zone is of fundamental importance in joint pathology. It includes the marginal cartilage and marginal synovium. The normal marginal synovium takes part in articular cartilage repair (Adachi et al. 2012). The inflamed marginal synovium, in turn, promotes irreversible damage to the adjacent cartilage and bone (Hitchon & El-Gabalawy, 2011). Objectives The morphology of the normal marginal synovium from birth till the 90th day was studied using the hip joints of Wistar rats. Methods The collection of joints was carried out on the first, seventh, 14th, 30th, 45th, 60th and 90th day (six rats in each group, 42 in total). Joints were fixed, decalcified and dehydrated. Histologic paraffine sections were stained with Mallory's trichrome and Hart's elastin staining, analyzed at the acetabular labrum by light microscopy (χ100), morphometrical and statistical (P < 0.05) methods with extrapolation to humans (Sengupta, 2013). The obtained data were presented as percentages. Results In the marginal synovium, cells and components of the extracellular matrix, which are typical for fibrous connective tissue, could be distinguished. The synovial lining cells are embedded in the modified basement membrane which is a meshwork of collagen and elastic fibers. They form a three-dimensional reticulum in it and adjacent synovial subintima. Vessels of the microcirculatory bed are also widely represented in the marginal synovium. The overall quantity of collagen fibers increased gradually, exceeding on the 90th day (∼18–19 human years) that of newborns by one and a half times (48.92 ± 3.39 vs 72.17 ± 7.77; P = 0.023). The number of arranged collagen fibers increased gradually, exceeding on the 90th day that of newborns almost twofold (37.25 ± 3.21 vs 60.08 ± 5.99; P = 0.008). The area of distribution of disarranged collagen fibers in newborns was almost four and a half times less than the overall quantity of collagen fibers (11.67 ± 1.03 vs 48.92 ± 3.39; P < 0.001) and did not change substantially throughout the experiment. The number of elastic fibers increased till the 30th day (0.63 ± 0.11 vs 18.3 ± 1.25; P < 0.001) and did not undergo significant changes later. In newborns, the area of distribution of ground substance was not considerably higher than the ratio of disarranged collagen fibers (10.42 ± 1.8 vs 11.67 ± 1.03; P = 0.562) and did not undergo substantial changes later. The distribution density of vessels increased till the 30th-45th day (4.5 ± 0.67 vs 7.5 ± 0.82 and 7.7 ± 0.54; P < 0.001; ∼9-14th human years), followed by a gradual decrease from the 60th day (7.05 ± 0.72; ∼16 human years). The maximum number of cells was in newborns. Subsequently, it gradually decreased and was almost three times less on the 90th day than that of newborns (38.01 ± 3.06 vs 12.58 ± 1.53; P < 0.001). Conclusion The morphogenesis of the marginal synovium during the postnatal period is accompanied by a gradual decrease in the number of cells, an increase in the area occupied by elastic and arranged collagen fibers with a relatively constant distribution density of disarranged collagen fibers and ground substance together with an undulatory pattern in the distribution of vessels. These peculiarities emphasize the morphological uniqueness of the marginal transitional zone, which forms the innate nonspecific barrier between the joint capsule and the articular cartilage, and thereby provides the necessary anatomical and physiological integrity of the joint as a whole organ. Knowledge about the patterns of morphogenesis of the normal marginal synovium will help to understand joint pathology. Ethics The study was approved by the ethics committee of the Zaporizhzhia State Medical University.

EFFECT OF REINFORCEMENT CORROSION ON THE PUNCHING SHEAR OF RC SLABS INCORPORATING MACRO SYNTHETIC FIBERS

This paper is part of an ongoing research on the effect of discrete fiber reinforcement on punching shear strength of reinforced concrete (RC) slabs subjected to accelerated corrosion regime of steel reinforcement. Results obtained from RC slabs incorporating macro synthetic fibers will be presented. Six RC slabs (1500 mm ×1500 mm ×100 mm) were prepared with a constant reinforcing steel ratio and incorporating synthetic fibers at different dosages (0.0 %, 0.5% and 0.75% by volume). The corroded set of slabs were subjected to an impressed current (IC) accelerated corrosion regime for 36 days with an applied constant current density of 500 µA/cm2. The slabs were subjected to wetting-drying cycles of 1 day wet and 2 days dry. During the wet cycle, the slabs were fully submerged in a 3.5% NaCl solution. The applied current results in a theoretical mass loss of steel by around 7%. The slabs were tested in a simply supported configuration until failure. The measured test parameters included the applied load, the slab deflection, and monitored the observed cracking. The results showed that reinforcement corrosion affected the slabs' performance in terms of strength and deflection capacities, as well as the cracking behavior. The load-deflection response showed that the addition of synthetic fibers could reduce the impact of steel corrosion on the punching shear behavior of the RC slab. Furthermore, the presence of synthetic fibers significantly limited the development of corrosion activity in the slabs by delaying corrosion-induced cracks when compared to the control slabs.

EFFECT OF REINFORCEMENT CORROSION ON THE PUNCHING SHEAR OF RC SLABS INCORPORATING MACRO SYNTHETIC FIBERS

This paper is part of an ongoing research on the effect of discrete fiber reinforcement on punching shear strength of reinforced concrete (RC) slabs subjected to accelerated corrosion regime of steel reinforcement. Results obtained from RC slabs incorporating macro synthetic fibers will be presented. Six RC slabs (1500 mm ×1500 mm ×100 mm) were prepared with a constant reinforcing steel ratio and incorporating synthetic fibers at different dosages (0.0 %, 0.5% and 0.75% by volume). The corroded set of slabs were subjected to an impressed current (IC) accelerated corrosion regime for 36 days with an applied constant current density of 500 µA/cm2. The slabs were subjected to wetting-drying cycles of 1 day wet and 2 days dry. During the wet cycle, the slabs were fully submerged in a 3.5% NaCl solution. The applied current results in a theoretical mass loss of steel by around 7%. The slabs were tested in a simply supported configuration until failure. The measured test parameters included the applied load, the slab deflection, and monitored the observed cracking. The results showed that reinforcement corrosion affected the slabs' performance in terms of strength and deflection capacities, as well as the cracking behavior. The load-deflection response showed that the addition of synthetic fibers could reduce the impact of steel corrosion on the punching shear behavior of the RC slab. Furthermore, the presence of synthetic fibers significantly limited the development of corrosion activity in the slabs by delaying corrosion-induced cracks when compared to the control slabs.

Long-term stability of graphene/c-Si Schottky-junction solar cells

A long operational lifetime is required for the use of solar cells in real-life photovoltaic applications. The optimization of operational lifetimes is achieved through understanding the inherent degradation phenomena in solar cells. In this study, graphene/Si Schottky-junction solar cells were produced, utilizing liquid-phase-exfoliated graphene as an active surface. The operational and interface stability of these solar cells over a period of 5 years in ambient conditions (following ISOS-D protocols: dark storage/shelf life) was examined, and the origin of their degradation was reported. It was found that the dominant degradation mechanism could be attributed to the degradation of silver contacts. This was indicated by a decrease in shunt resistance, an increase in the ideality factor (due to a higher carrier recombination), and a constant defect density in graphene films for up to 4 years. Measurements across the solar cell's active area during the 5-year period revealed neither significant spatial inhomogeneity, nor shunt channel defects.

A General Model for Thermodynamic Properties of Fluid Mixtures Based on Helmholtz Energy Formulations for the Components. Virial Expansion and Reduction to van der Waals Mixing Rules

Over the recent decades, Helmholtz energy formulations became available for a broad range of fluids. These multiparameter equations of state (R. Span, Springer 2000) allow computation of thermodynamic properties essentially within the experimental errorbars. Corresponding states-based model by Lemmon and Tillner-Roth (Fluid Phase Equilib 165:1, 1999) enabled construction of Helmholtz energy formulations for mixtures. However, we show that this model generates a non-physical dependence of virial coefficients on composition, which can be strong when the components are dissimilar. We propose a new mixture model that overcomes this deficiency. It has two main ingredients: (i) Quadratic mixing of “Helmholtz volumities”. This quantity with units of molar volume is introduced as a ratio of the molar residual Helmholtz energy to a product of gas constant, thermodynamic temperature, and molar density. It reduces to the second virial coefficient in the zero-density limit. Helmholtz volumities are considered for components and “cross-components”, hypothetical fluids representing the binary interactions. (ii) Replacing the variables—reduced reciprocal temperatures and reduced densities—with temperature and density scaling functions. Different scaling functions can be used for different components and cross-components, thus providing a highly flexible framework for representing the properties of mixtures. The scaling functions must be expandable into Taylor series in terms of molar concentrations in the zero-density limit. For the proposed mixture model, we develop formulas for computing virial coefficients up to the fourth order. Furthermore, we show that when the proposed mixture model is applied to a cubic equation of state, the conventional van der Waals mixing rules can be retrieved. These findings allow to consider the new model as a viable alternative to the corresponding states method of modeling thermodynamic properties of fluid mixtures.

Push-pull mechanics of E-cadherin ectodomains in biomimetic adhesions

E-cadherin plays a central role in cell-cell adhesion. The ectodomains of wild-type cadherins form a crystalline-like two-dimensional lattice in cell-cell interfaces mediated by both trans (apposed cell) and cis (same cell) interactions. In addition to these extracellular forces, adhesive strength is further regulated by cytosolic phenomena involving α and β catenin-mediated interactions between cadherin and the actin cytoskeleton. Cell-cell adhesion can be further strengthened under tension through mechanisms that have not been definitively characterized in molecular detail. Here we quantitatively determine the role of the cadherin ectodomain in mechanosensing. To this end, we devise an E-cadherin-coated emulsion system, in which droplet surface tension is balanced by protein binding strength to give rise to stable areas of adhesion. To reach the honeycomb/cohesive limit, an initial emulsion compression by centrifugation facilitates E-cadherin trans binding, whereas a high protein surface concentration enables the cis-enhanced stabilization of the interface. We observe an abrupt concentration dependence on recruitment into adhesions of constant crystalline density, reminiscent of a first-order phase transition. Removing the lateral cis interaction with a “cis mutant” shifts this transition to higher surface densities leading to denser, yet weaker adhesions. In both proteins, the stabilization of progressively larger areas of deformation is consistent with single-molecule experiments that show a force-dependent lifetime enhancement in the cadherin ectodomain, which may be attributed to the “X-dimer” bond.

Reinforced energy storage performance of poly(vinylidene fluoride) composite films by filling with surface fluorinated one-dimensional barium titanate nanofibers

One-dimensional barium titanate nanofibers/poly(vinylidene fluoride) (PVDF) composite films were prepared by casting technology. To improve the dispersion of nanofibers in the PVDF matrix and enhance the interface bonding between nanofibers and the PVDF matrix, surface modification of nanofibers was obtained by fluorination treatment. Experimental and theoretical simulation studies were conducted to investigate the effects of surface fluorination-modified one-dimensional barium titanate nanofibers on the micro morphology, structure, dielectric constant, and energy storage density of PVDF composite films. The results showed that the barium titanate powder synthesized by electrospinning had a good one-dimensional fiber morphology, with a diameter of 70–130 nm and a length of 4–15 µm. The surface fluorination treatment was able to significantly improve the dispersion and bonding of the one-dimensional barium titanate nanofiber in the PVDF matrix. As the filling volume of the one-dimensional nanofibers increased, the dielectric constant of the PVDF composite film significantly increased. When the filling volume of the surface fluorinated one-dimensional barium titanate nanofiber was 7.5 vol%, the room temperature dielectric constant of the PVDF composite film reached 21.8, and the surface fluorinated one-dimensional barium titanate nanofiber/PVDF composite film exhibited lower dielectric loss and high breakdown strength. When the filling volume of the surface fluorinated one-dimensional barium titanate nanofiber was 2.5 vol%, the energy storage density of the PVDF composite film was 7.9 J/cm3, which was 2.82 times that of pure PVDF. The improvement of energy storage performance can be attributed to the good dispersion of the surface fluorinated barium titanate nanofibers in the PVDF matrix and the good interface situation. Finite element simulation further revealed that the surface fluorinated one-dimensional nanofibers could effectively improve the breakdown strength of the composites. That provides a promising way to enhance the dispersion and interface bonding of filler in polymer matrices, thereby achieving high-performance composites with high dielectric constant, high breakdown strength, and excellent energy storage density.

Processing defect, microstructure evolution and mechanical properties of laser powder bed fusion Al-12Si alloys

The laser power and scan speed are significant processing parameters influencing the defects and microstructures due to affecting the thermal state within the melt pool during laser powder bed fusion (LPBF). To this end, these process parameter combinations under a constant laser energy density are correlated with defects (balling phenomenon and pores) and microstructures (melt pool arrangement and cell morphology). Setting the parameter combination (laser power and scan speed are 200 W and 910 mm/s, respectively) yields large balling droplets (average size of 150 μm) due to the relatively high melt viscosity resulting from the low melt pool temperature. In this case, a limited surface tension difference acting on a liquid surface cannot provide sufficient driving forces against viscous drags to promote the efficient spreading of the molten alloy. Cavity regions are formed between the large balling droplets and the previous layer, forming lack-of -fusion pores. By increasing the laser power and scan speed gradually, samples with relative densities greater than 99.5% are produced. This phenomenon can be attributed to the increases in laser power and scan speed, which improves the spreading ability of the molten alloy. With increasing laser power and scan speed, the cell size decreases (from 0.51 μm to 0.42 μm) because of the increase in the cooling rate. The sample (laser power and scan speed are 350 W and 1590 mm/s, respectively) has the highest performance (310 MPa yield strength, 470 MPa ultimate tensile strength, and 6.6% fracture strain) due to its highest relative density (greater than 99.5%) and fine microstructure (average cell size of 0.45 μm). All four samples exhibit anisotropic mechanical properties resulting from the combination of the melt pool boundary and lack-of-fusion pores.

Quantum energy inequalities along stationary worldlines

Quantum energy inequalities (QEIs) are lower bounds on the averaged energy density of a quantum field. They have been proved for various field theories in general curved spacetimes but the explicit lower bound is not easily calculated in closed form. In this paper we study QEIs for the massless minimally coupled scalar field in four-dimensional Minkowski spacetime along stationary worldlines—curves whose velocity evolves under a 1-parameter Lorentz subgroup—and find closed expressions for the QEI bound, in terms of curvature invariants of the worldline. Our general results are illustrated by specific computations for the six prototypical stationary worldlines. When the averaging period is taken to infinity, the QEI bound is consistent with a constant energy density along the worldline. For inertial and uniformly linearly accelerated worldlines, this constant value is attained by the Minkowski and Rindler vacuums respectively. It is an open question as to whether the bounds for other stationary worldlines are attained by other states of interest.

Phase formation and electrical properties of SBNLT ceramics prepared via combustion technique

This report investigates the effect of firing temperatures on the phase formation, microstructure, electrical, and energy storage properties of lead-free Sr0.3(Bi0.7Na0.67Li0.03)0.5TiO3 (SBNLT) ceramics, synthesised by combustion technique. The samples were calcined between 700°C and 900°C for 2 h and sintered between 1100°C and 1200°C for 2 h. The ceramics exhibited coexisting rhombohedral and tetragonal phases, which were confirmed by the Rietveld refinement technique. A morphotropic phase boundary (MPB) of the rhombohedral and tetragonal phases, with a ratio of 49:51, was obtained at the sintering temperature of 1175°C. The highest maximum dielectric constant (ε max = 4667), polarisation (P max = 28.80 µC/cm2) and energy density (W = 0.95 J/cm3), with a breakdown strength of 70 kV/cm, were achieved from the sample sintered at 1175°C.