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The microscopic Bouligand-type architectures of fish scales demonstrate a notable efficiency in enhancing the damage tolerance of materials; nevertheless, it is challenging to reproduce in metals. Here bioinspired tungsten-copper composites with different Bouligand-type architectures mimicking fish scales were fabricated by infiltrating a copper melt into woven contextures of tungsten fibers. These composites exhibit a synergetic enhancement in both strength and ductility at room temperature along with an improved resistance to high-temperature oxidization. The strengths were interpreted by adapting the classical laminate theory to incorporate the characteristics of Bouligand-type architectures. In particular, under load the tungsten fibers can reorient adaptively within the copper matrix by their straightening, stretching, interfacial sliding with the matrix, and the cooperative kinking deformation of fiber grids, representing a successful implementation of the optimizing mechanisms of the Bouligand-type architectures to enhance strength and toughness. This study may serve to promote the development of new high-performance tungsten-copper composites for applications, e.g., as electrical contacts or heat sinks, and offer a viable approach for constructing bioinspired architectures in metallic materials.

The replacement of synthetic foam materials using natural biological ones is of great significance for saving energy/resources and reducing environmental pollutions. Here we characterized the microstructure and mechanical properties of natural cornstalk pith, which has a large annual output yet lacks an effective exploitation, and evaluated its feasibility for applications as a substitute for synthetic foam materials. The cornstalk pith was revealed to be a cellular material composed of closed cells elongated along the growth direction of corn plant and reinforced by well-aligned vascular bundles penetrating the foam matrix. The compressive behavior is featured by a stable stress plateau which is favorable for energy absorption with its mechanical properties largely dependent on the hydration state and loading configuration. In particular, the initial dimension and mechanical properties of cornstalk pith can be effectively recovered after deformation simply by hydration treatment owing to swelling effect caused by the turgor pressure from osmosis. The cornstalk pith demonstrates an outstanding combination of low density and high energy absorption efficiency among various foam materials, specifically with its plateau stress and energy absorption comparable or even superior to those of some typical synthetic foam materials. These along with the huge resources and good biodegradability make it a promising natural energy absorbing cellular material for replacing synthetic counterparts.

Replicating the architecture of natural nacre has become an important approach for enhancing the damage tolerance of man-made materials. Nevertheless, this is principally limited to systems composed of chemically different constituents and demonstrates a difficulty in realizing structural hierarchy at multiple length-scales. Here a proof of concept is presented about the implementation of bioinspired nacre-like designs in a hybrid composite of pure carbon comprising its two basic allotropic forms, i.e., natural graphite flakes and amorphous carbon from the carbonization of organics. Multiscale micro/nano-architectures with three levels of hierarchy were constructed in the composite based on the preferential alignment of graphite flakes using bidirectional freeze casting method. The composite exhibited a remarkable mechanical efficiency, specifically featured by good damage tolerance with rising R-curve behavior, owing to the activation of hierarchical toughening mechanisms at micro to nano length-scales. This verifies the potency of nacre-inspired designs for generating enhanced fracture toughness in carbon systems, even using simple raw materials, which is significant for promoting their structural applications.

Porous gypsum materials are of notable significance and demonstrate a broad application in construction and biomedical engineering; nevertheless, it is challenging to simultaneously enhance their mechanical and functional properties. Here by replicating the designs of natural wood, new gypsum materials containing unidirectional micro-pores were fabricated by employing a modified ice-templating technique. The retention of ice-templated architectures was realized based on the hydration-induced self-hardening characteristic of gypsum without using the traditionally long-time freeze drying treatment. The porosities of the wood-like gypsum can be readily adjusted in wide ranges from lower than 60 vol.% to over 80 vol.% by controlling the solid loads in initial slurries. The wood-like gypsum exhibits a notable improvement in compressive strength and energy absorption efficiency along the lamellar direction by more than twofold compared to the unfrozen gypsum materials containing random pores of similar porosity. Additionally, it displays the lowest level of thermal conductivity among gypsum materials along the normal direction of lamellae, which ranges from above 0.21 to ~0.1 W (m K)−1 depending on porosity, thereby demonstrating an outstanding effectiveness for thermal insulation. It can also be easily modified from hydrophilic to hydrophobic towards enhanced water resistance. The high strength and multi-functionalities along with the feasible fabrication approach make the wood-like gypsum appealing for applications, e.g., as construction and biomedical materials. The unidirectionally open pores may also provide new possibilities for regulating the cell behavior in gypsum-based bone implants.

Operating mainly as a type of weapon, the beetle horn develops an impressive mechanical efficiency based on chitinous materials to maximize the injury to opponent and simultaneously minimize the damage to itself and underlying brain under stringent loading conditions. Here the cephalic horn of the beetle Allomyrina dichotoma is probed using multiscale characterization combined with finite element simulations to explore the origins of its biomechanical functionality from the perspective of materials science. The horn is revealed to be highly regulated from the macroscopic shape, geometry, and connection with the body to the meso- and microscopic architecture, moisture content, and chemical and structural characteristics. Varying kinds of gradients are integrated at all length-scales. Such designs are demonstrated to benefit the mechanical performance by mitigating stress concentrations, retarding crack propagation, and modulating local properties to better adapt to stress. Enhanced rigidity, robustness and stability are additionally generated from the constrained flexibility endowed by the nanocomposite plywood structure through the reorientation of chitin nanofibrils within the proteinaceous matrix. These findings shed light on the intriguing materials-design strategies of nature in creating synergy of offence and persistence. They may even offer inspiration for the synthesis of high-performance materials and structures, in particular beams to resist bending and torsion.

Crustacean exoskeletons demonstrate exceptional mechanical efficiency owing to their intricate architectures. However, the translation of their underlying structural design to man-made material sys...

Taking lessons from nature offers an increasing promise toward improved performance in man‐made materials. Here new cement materials with unidirectionally porous architectures are developed by replicating the designs of natural wood using a simplified ice‐templating technique in light of the retention of ice‐templated architectures by utilizing the self‐hardening nature of cement. The wood‐like cement exhibits higher strengths at equal densities than other porous cement‐based materials along with unique multifunctional properties, including effective thermal insulation at the transverse profile, controllable water permeability along the vertical direction, and the easy adjustment to be water repulsive by hydrophobic treatment. The strengths are quantitatively interpreted by discerning the effects of differing types of pores using an equivalent element approach. The simultaneous achievement of high strength and multifunctionality makes the wood‐like cement promising for applications as new building materials, and verifies the effectiveness of wood‐mimetic designs in creating new high‐performance materials. The simple fabrication procedure by omitting the freeze‐drying treatment can also promote a better efficiency of ice‐templating technique for the mass production in engineering and may be extended to other material systems., By learning from natural wood, new cement materials with unidirectionally porous architectures are developed using a simplified ice‐templating technique. The wood‐like cement exhibits markedly higher strengths at equal densities than conventional cement materials. This is accompanied by a simultaneous achievement of multifunctional properties, including effective thermal insulation, controllable water permeability, and easy adjustment between hydrophilic and hydrophobic characteristics.

With the commercialization of wide-bandgap (WBG) semiconductor devices, the design strategy of medium-voltage inverters has to change. This paper compares SiC MOSFET in two medium-voltage multilevel inverters: Flying Capacitor Converter (FCC) and Modular Multilevel Converter (MMC). Both topologies have a single DC source and floating capacitors. Capacitor selection and power loss analysis are compared and the simulation results of both topologies are presented. The result shows that FCC is superior in terms of power density because the capacitor size of the FCC is directly related to the switching frequency whereas the capacitor size of the MMC is related to AC line frequency. FCC also has fewer switching devices and capacitors, and better utilization of switching devices. On the other hand, the MMC has better modularity, lower capacitor current, lower total harmonic distortion (THD), and a more mature voltage-balance strategy. The efficiency of both topologies is comparable.

A 3D printed magnesium alloy with an interpenetrating NiTi phase shows remarkable strength, damping, and self-healing properties., It is of significance, but still remains a key challenge, to simultaneously enhance the strength and damping capacities in metals, as these two properties are often mutually exclusive. Here, we provide a multidesign strategy for defeating such a conflict by developing a Mg-NiTi composite with a bicontinuous interpenetrating-phase architecture through infiltration of magnesium melt into three-dimensionally printed Nitinol scaffold. The composite exhibits a unique combination of mechanical properties with improved strengths at ambient to elevated temperatures, remarkable damage tolerance, good damping capacities at differing amplitudes, and exceptional energy absorption efficiency, which is unprecedented for magnesium materials. The shape and strength after deformation can even be largely recovered by heat treatment. This study offers a new perspective for the structural and biomedical applications of magnesium.

This paper presents: 1) a modulation method that combine active-zero PWM and conventional Space-Vector PWM (SVPWM) for three-level inverter, 2) a simplified DC capacitor active voltage-balance algorithm with common-mode voltage reduction using proposed modulation method. The presented modulation method and voltage-balance algorithm simplified calculation of both DC capacitor voltage balance and PWM generation, and take AC load current into consideration, which is suitable for wider range of load condition. In addition, both proposed methods can be programmed as add-on function of conventional SVPWM, which allow online enable/disable during operation of inverter for more flexible system control. The performance of proposed methods are demonstrated in both computer simulation and prototype test. A patent has been granted for the proposed methods and has been adopted in an industrial wide-bandgap semiconductor based PV prototype.

The tooth enamel of vertebrates comprises a hyper-mineralized bioceramic, but is distinguished by an exceptional durability to resist impact and wear throughout the lifetime of organisms; however, enamels exhibit a low resistance to the initiation of large-scale cracks comparable to that of geological minerals based on fracture mechanics. Here we reveal that the tooth enamel, specifically from the giant panda, is capable of developing durability through counteracting the early stage of damage by partially recovering its innate geometry and structure at nano- to micro- length-scales autonomously. Such an attribute results essentially from the unique architecture of tooth enamel, specifically the vertical alignment of nano-scale mineral fibers and micro-scale prisms within a water-responsive organic-rich matrix, and can lead to a decrease in the dimension of indent damage in enamel introduced by indentation. Hydration plays an effective role in promoting the recovery process and improving the indentation fracture toughness of enamel (by ∼73%), at a minor cost of micro-hardness (by ∼5%), as compared to the dehydrated state. The nano-scale mechanisms that are responsible for the recovery deformation, specifically the reorientation and rearrangement of mineral fragments and the inter- and intra-prismatic sliding between constituents that are closely related to the viscoelasticity of organic matrix, are examined and analyzed with respect to the structure of tooth enamel. Our study sheds new light on the strategies underlying Nature's design of durable ceramics which could be translated into man-made systems in developing high-performance ceramic materials. STATEMENT OF SIGNIFICANCE: Tooth enamel plays a critical role in the function of teeth by providing a hard surface layer to resist wear/impact throughout the lifetime of organisms; however, such enamel exhibits a remarkably low resistance to the initiation of large-scale cracks, of hundreds of micrometers or more, comparable to that of geological minerals. Here we reveal that tooth enamel, specifically that of the giant panda, is capable of partially recovering its geometry and structure to counteract the early stages of damage at nano- to micro-scale dimensions autonomously. Such an attribute results essentially from the architecture of enamel but is markedly enhanced by hydration. Our work discerns a series of mechanisms that lead to the deformation and recovery of enamel and identifies a unique source of durability in the enamel to accomplish this function. The ingenious design of tooth enamel may inspire the development of new durable ceramic materials in man-made systems.

For composite materials applied for energy absorption and vibration/noise reduction, it is of particular significance to clarify the role of strain rate and temperature on their mechanical properties. Here we present a study on the effects of strain rate (from 10−3 s−1 to 1 s−1) and temperature (from room temperature to 350 °C) on the compressive properties of a 3-D printed Mg–NiTi interpenetrating-phase composite, which features high energy absorption efficiency and good damping capacity. Within the regimes of strain rate and temperature, the composite constantly exhibits a stable stress plateau on the stress-strain curves, yet displays markedly different damage mechanisms depending on the specific strain rate and temperature. The 3-D interpenetrating-phase architecture promotes an effective stress transfer in the composite and resists the propagation of local damages, thereby conferring a high strengthening efficiency and outstanding damage tolerance. The unique combination of mechanical properties makes the composite appealing for applications under various conditions, especially for absorbing mechanical energy and reducing vibrations and noise.

The structures of tungsten and tungsten carbide scaffolds play a key role in determining the properties of their infiltrated composites for multifunctional applications. However, the architectural construction of W/WC systems is challenging because of the difficulty of assembly due to their large densities. Here we present the generation of unidirectionally porous architectures, with high porosities exceeding 65%, for W and WC scaffolds using direct ice-templating techniques, which in many respects reproduce the design motif of wood. This was achieved by adjusting the viscosities of suspensions to retard sedimentation during freezing. The processing, structural characteristics and mechanical properties of the resulting scaffolds were investigated and the correlations between them explored. Quantitative relationships were established to describe their strengths based on a simple model taking into account both inter- and intra-lamellar pores. The fracture mechanisms were also identified, especially in light of the porosity. This study extends the effectiveness of ice-templating techniques for systems with large densities or particle sizes. It further provides preforms for developing new nature-inspired multifunctional materials, as represented by W/WC-Cu composites.

Living organisms are adept at resisting contact deformation and damage by assembling protective surfaces with spatially varied mechanical properties, i.e. , by creating functionally graded materials. Such gradients, together with multiple length-scale hierarchical structures, represent the two prime characteristics of many biological materials to be translated into engineering design. Here, we examine one design motif from a variety of biological tissues and materials where site-specific mechanical properties are generated for enhanced protection by adopting gradients in structural orientation over multiple length-scales, without manipulation of composition or microstructural dimension. Quantitative correlations are established between the structural orientations and local mechanical properties, such as stiffness, strength and fracture resistance; based on such gradients, the underlying mechanisms for the enhanced protective role of these materials are clarified. Theoretical analysis is presented and corroborated through numerical simulations of the indentation behavior of composites with distinct orientations. The design strategy of such bioinspired gradients is outlined in terms of the geometry of constituents. This study may offer a feasible approach towards generating functionally graded mechanical properties in synthetic materials for improved contact damage resistance. Statement of Significance Living organisms are adept at resisting contact damage by assembling protective surfaces with spatially varied mechanical properties, i.e. , by creating functionally-graded materials. Such gradients, together with multiple length-scale hierarchical structures, represent the prime characteristics of many biological materials. Here, we examine one design motif from a variety of biological tissues where site-specific mechanical properties are generated for enhanced protection by adopting gradients in structural orientation at multiple length-scales, without changes in composition or microstructural dimension. The design strategy of such bioinspired gradients is outlined in terms of the geometry of constituents. This study may offer a feasible approach towards generating functionally-graded mechanical properties in synthetic materials for improved damage resistance.

Self-healing capacity, of which the inspiration comes from biological systems, is significant for restoring the mechanical properties of materials by autonomically repairing damages. Clarifying the naturally occurring self-healing behaviors and mechanisms may provide valuable inspiration for designing synthetic self-healing materials. In this study, water-assisted self-healing behavior was revealed in a natural dermal armor of pangolin scales. The indentation damages which imitate the injury caused by predatory attack can be continuously mitigated through hydration. The healing kinetics was characterized according to the variations of indentation crater dimension and quantitatively described in terms of the viscoelastic behavior of biopolymer. The mechanical properties of original, damaged, and recovered scales in both dry and wet states were systematically evaluated by three-point bending and compared through statistical analysis. The hydration effects and mechanisms were explored by examining the dynamic mechanical properties and thermal behaviors. The promoted self-healing process can be attributed to the improved flexibility of macromolecules in the biopolymer. This study may stimulate useful self-healing strategies in bio-inspired design and aid in developing high-performance synthetic self-healing materials.

Remarkable water-stimulated shape memory effect was revealed in a natural biopolymer of peacock's tail covert feathers of which the innate shape can almost be fully recovered after severe deformation by a short hydration step. The shape memory effect manifests a good stability of high recovery rate and ratio during cycles of deformation and subsequent recovery. Both strength and energy absorption efficiency of medullary foam can be recovered despite the apparent decrease in the first deformation stroke caused by structural damage. A kinetic model developed from non-equilibrium thermodynamic fluctuation theory was adopted to describe the shape recovery process by considering the viscoelastic relaxation. The effects of hydration on mechanical properties, recovery kinetics, activation process and dynamic mechanical behaviors were also evaluated. Mechanisms were explored based on the lubrication, swelling effect and structural changes of macromolecular chains or segments in terms of their mobility. This study is expected to aid in understanding the responses of natural biological materials to environmental stimuli and to provide useful information for synthetic shape memory materials from the bio-inspiration perspective.

Feather shaft, which is primarily featured by a cylinder filled with foam, possesses a unique combination of mechanical robustness and flexibility with a low density through natural evolution and selection. Here the hierarchical structures of peacock’s tail coverts shaft and its components are systematically characterized from millimeter to nanometer length scales. The variations in constituent and geometry along the length are examined. The mechanical properties under both dry and wet conditions are investigated. The deformation and failure behaviors and involved strengthening, stiffening and toughening mechanisms are analyzed qualitatively and quantitatively and correlated to the structures. It is revealed that the properties of feather shaft and its components have been optimized through various structural adaptations. Synergetic strengthening and stiffening effects can be achieved in overall rachis owing to increased failure resistance. This study is expected to aid in deeper understandings on the ingenious structure–property design strategies developed by nature, and accordingly, provide useful inspiration for the development of high-performance synthetic foams and foam-filled materials.

Polymethyl methacrylate (PMMA) is one of important engineering materials and has been widely applied in various fields. Owing to the catastrophically brittle fracture nature, exploring the fracture mechanism of PMMA is of crucial significance to guide its engineering application. In this work, tensile tests with several kinds of sample geometries including unnotched samples and notch samples with different widths were designed to systematically investigate the macroscopic bifurcation of PMMA. Based on the sufficient experimental evidences, the traditional critical stress intensity criterion was found inappropriate for predicting the macroscopic bifurcation of PMMA. Finally, the fracture features were explicitly clarified based on the detailed experimental observations, and a new explanation to elucidate the fracture mechanism of PMMA was proposed.

According to the development status of fixed facilities in railway marshalling yards and the relationships among the different fixed facilities, the indicator system about the coordination assessment of fixed facilities’ capacity in railway marshalling yards was established. The C2R model of data envelopment analysis (DEA) was used in the coordination assessment, and the model was solved with MATLAB programming. The result of the analysis is generally consistent with the actual situation.

Based on the operation and management of station, the research was mainly about the risk assessment method of the crowd crushing and tramping accidents in urban rail transit stations. The indicator system about the crowd crushing and tramping accidents in urban rail transit station was established. The C2R model of data envelopment analysis (DEA) was used in the risk assessment, and the model was solved with MATLAB programming. The result of the analysis is generally consistent with the actual situation.

This paper discusses the modeling and application of thermoelectric cooling (TEC) in power electronics circuits. To investigate the benefits and challenges of using TEC, a temperature-dependent thermoelectric model which includes both power electronics circuits and TEC device is presented. With this model, both steady-state and small signal analyses can be carried out, and this paper is more focused on the steady-state part. For the steady-state analysis, the results have identified the allowed operation range which could be used as guidelines for system design. Also, with TEC device, the case temperature and junction temperature of power electronics switches can be dynamically controlled. Therefore, the switches' thermal cycling problem could be alleviated, and the switch lifetime and overall system reliability will be improved. Both simulation and experimental results are presented in this paper to verify the analysis.

Making replacements for the human body similar to natural tissue offers significant advantages but remains a key challenge. This is pertinent for synthetic dental materials, which rarely reproduce the actual properties of human teeth and generally demonstrate relatively poor damage tolerance. Here new bioinspired ceramic-polymer composites with nacre-mimetic lamellar and brick-and-mortar architectures are reported, which resemble, respectively, human dentin and enamel in hardness, stiffness, and strength and exhibit exceptional fracture toughness. These composites are additionally distinguished by outstanding machinability, energy-dissipating capability under cyclic loading, and diminished abrasion to antagonist teeth. The underlying design principles and toughening mechanisms of these materials are elucidated in terms of their distinct architectures. It is demonstrated that these composites are promising candidates for dental applications, such as new-generation tooth replacements. Finally, it is believed that this notion of bioinspired design of new materials with unprecedented biologically comparable properties can be extended to a wide range of material systems for improved mechanical performance.

The nacre of mollusk shells is distinguished by an exceptional mechanical efficiency which is derived essentially from its lamellar structure and frequently acts as a source of inspiration for the development of biomimetic materials. The structure and mechanical properties of nacre have been intensively investigated with a special focus on its toughening strategies; nevertheless, the fracture mechanisms, more specifically the critical stress/strain conditions for the failure of nacre, and the effects of structural orientation and hydration state remain largely unexplored. Here uniaxial compression tests were performed on nacre of both dry and hydrated states with different off-axis angles, i.e., the inclination of loading axis with respect to the lamellar structure, ranging from 0° to 90°. The mechanical properties and fracture characteristics of nacre and their dependences on the structural orientation and hydration state were elucidated in terms of mechanics behind failure. Quantitative relationships were established between the mechanical properties and off-axis angle based on different failure criteria. The competition between the fracture modes of fragmentation and shearing was quantified by comparing their respective driving force and resistance on the interfacial plane. This study may aid the understanding on the mechanical behavior of nacre and nacre-inspired synthetic materials and promote a better replication of the underlying design principles of nacre in man-made systems.

The giant panda׳s teeth possess remarkable load-bearing capacity and damage resistance for masticating bamboos. In this study, the hierarchical structure and mechanical behavior of the giant panda׳s tooth enamel were investigated under indentation. The effects of loading orientation and location on mechanical properties of the enamel were clarified and the evolution of damage in the enamel under increasing load evaluated. The nature of the damage, both at and beneath the indentation surfaces, and the underlying toughening mechanisms were explored. Indentation cracks invariably were seen to propagate along the internal interfaces, specifically the sheaths between enamel rods, and multiple extrinsic toughening mechanisms, e.g., crack deflection/twisting and uncracked-ligament bridging, were active to shield the tips of cracks from the applied stress. The giant panda׳s tooth enamel is analogous to human enamel in its mechanical properties, yet it has superior hardness and Young׳s modulus but inferior toughness as compared to the bamboo that pandas primarily feed on, highlighting the critical roles of the integration of underlying tissues in the entire tooth and the highly hydrated state of bamboo foods. Our objective is that this study can aid the understanding of the structure-mechanical property relations in the tooth enamel of mammals and further provide some insight on the food habits of the giant pandas.

The as-prepared alumina/silica (Al2O3/SiO2) composite nanoparticles were synthesized with a hydrothermal method and modified by silane coupling agent. The tribological properties of the modified Al2O3/SiO2 composite nanoparticles as lubricating oil additives were investigated by four-ball and thrust-ring tests in terms of wear scar diameter, friction coefficient, and the morphology of thrust-ring. It is found that their anti-wear and anti-friction performances are better than those of pure Al2O3 or SiO2 nanoparticles. When the optimized concentration of nanoparticle additive is 0.5 wt.%, the diameters of wear scar and friction coefficients are both smallest. Such modified composite nanoparticles can adsorb onto the friction surfaces, which results in rolling friction. Therefore, the friction coefficient is reduced.

Laminated structure reduces the common inverse relationship of strength and toughness in many biological materials. Here the mechanical behavior of pearl and nacre with spherical and flat laminations was investigated and compared with the geological aragonite counterpart. The biological ceramics demonstrate higher strength, better reliability, and improved damage resistance owing to their laminated arrangement. Kinking and delamination occur in pearl to resist damage in addition to the crack-tip shielding mechanisms as in nacre, such as crack deflection, bridging, and platelet pull-out. The fracture mechanisms were interpreted in terms of the stress state using finite element simulation. This study may help clarify the compressive mechanics of laminated sphere between platens and advance the understanding on the mechanical behavior of biological and bio-inspired laminated materials.

As natural flexible dermal armor, pangolin scales provide effective protection against predatory threats and possess other notable properties such as anti-adhesion and wear-resistance. In this study, the structure, mechanical properties, deformation and damage behaviors of pangolin scales were systematically investigated with the effects of hydration and orientation evaluated. The scales are divided into three macro-layers constituted by overlapping keratin tiles with distinct lamellar arrangements which are further composed of lower-ordered lamellae. Both hardness and strength are significantly decreased by hydration; while the plasticity is markedly improved concomitantly, and as such, the mechanical damages are mitigated. The tensile strength invariably approximates to one third of hardness in value. The tensile deformation is dominated by lamellae stretching and pulling out under wet condition, which is distinct from the trans-lamellar fracture in dry samples. The compressive behaviors are featured by pronounced plasticity in both dry and wet scales; and notable strain-hardening capacity is introduced by hydration, especially along the thickness direction wherein kinking occurs. Inter-lamellar cracking is effectively alleviated in wet samples compared with the dry ones and both of them deform by macroscopic buckling. This study may help stimulate possible inspiration for the design of high-performance synthetic armor materials by mimicking pangolin scales.

Flavonol synthase (FLS) is one of the key enzymes in flavonoids metabolic pathways. In this study, middle sequence was obtained from Carthamus tinctorius transcriptome sequencing results. Full-length cDNAs of FLS was cloned from petals of C. tinctorius to FLS by using RT-PCR and RACE technology. Its full-length cDNA was 1,201 bp, with an open reading frame of 1,101 bp and 336 encoded amino acids. The phylogenetic analysis showed that, FLS gene encoded amino acids in C. tinctorius were highly homologous with amino acids in congeneric Compositae species, especially Rudbeckia laciniata. The pBASTA-FLS plant expression vector was successfully built by the molecular biology method, which lays a foundation for further studying biology functions of the gene and biosynthesis mechanism of flavonoids.

Despite the extensive investigation on the structure of natural biological materials, insufficient attention has been paid to the structural imperfections by which the mechanical properties of synthetic materials are dominated. In this study, the structure of bivalve Saxidomus purpuratus shell has been systematically characterized quantitatively on multiple length scales from millimeter to sub-nanometer. It is revealed that hierarchical imperfections are intrinsically involved in the crossed-lamellar structure of the shell despite its periodically packed platelets. In particular, various favorable characters which are always pursued in synthetic materials, e.g. nanotwins and low-angle misorientations, have been incorporated herein. The possible contributions of these imperfections to mechanical properties are further discussed. It is suggested that the imperfections may serve as structural adaptations, rather than detrimental defects in the real sense, to help improve the mechanical properties of natural biological materials. This study may aid in understanding the optimizing strategies of structure and properties designed by nature and accordingly, provide inspiration for the design of synthetic materials.

Crossed-lamellar structure is one of the most common organizations found in mollusk shells and may serve as a natural mimetic model for designing bio-inspired synthetic materials. Nonetheless, the mechanical behaviors and corresponding mechanisms have rarely been investigated for individual macro-layer of such structure. The integrated effects of orientation and hydration also remain unclear. In this study, the mechanical behaviors and their structural dependences of pure crossed-lamellar structure in Saxidomus purpuratus shell were systematically examined by three-point bending and compression tests. Mechanical properties and fracture mechanisms were revealed to depend strongly on the orientation, hydration state and loading condition. Three basic cracking modes of inter-platelet, trans-platelet, and along the interfaces between first-order lamellae were identified, and the interfacial separation was enhanced by hydration. Macroscopic compressive fracture was accomplished through axial splitting during which multiple toughening mechanisms were activated. The competition among different cracking modes was quantitatively evaluated by analyzing their driving stresses and resistances from fundamental mechanics. This study helps to clarify the mechanical behaviors of naturally occurring crossed-lamellar structure, and accordingly, aids in designing new bio-inspired synthetic materials by mimicking it.

This paper presents a single phase, multilevel, three-port, switched capacitor inverter based on Gallium Nitride (GaN) devices from Transphorm. The features of this inverter include one 200 V dc port, and two ac ports, which are two-level 120 V (1X inverter) and three-level 240 V (2X inverter), respectively. This circuit harness the superior characteristics of GaN devices, especially their faster switching speed and lower on resistance, to reduce the passive components size, increase overall power density, and achieve multiport operation. In this paper, complete circuit description, operation principles and device evaluation are provided. Also, to verify proposed functions, a 2 kW prototype has been built and the preliminary testing results have shown a 98.5% peak efficiency with two ac outputs.

This paper discusses the modeling and application of Thermoelectric Cooling (TEC) in power electronics circuits, with the focus on the small signal modeling and controller design. In this paper, the small signal analysis based on a comprehensive thermoelectric model is carried out and the results show that, the whole system is a non-minimum-phase system and lack of damping to the disturbance in the control variable. A closed loop controller is designed to solve the stability issues and realize dynamic temperature control. To verify the effectiveness of derived small signal model and designed controller, an 8 kW prototype has been built and experimental results are presented in this paper.

This paper discusses the modeling and application of Thermoelectric Cooling (TEC) in power electronics circuits. To investigate the benefits and challenges of using TEC, a comprehensive thermoelectric model which includes both power electronics circuit and TEC device is presented. With this model, the optimal operation range and dynamic base temperature control of power electronics switches are analyzed. The results show that with TEC, the base temperature of power electronics switches can maintain almost constant under different load conditions. Therefore, the switch lifetime and overall system reliability will be improved. Both simulation and experimental results are presented in this paper to verify the analysis.

In this paper, two methods are proposed and analyzed for detailed modeling of power electronic devices and converters in real time using an FPGA. First, a Thevenin equivalent switch representation is enhanced to model the on characteristics of switching devices. Using this approach, an algorithm for real time electro-thermal modeling of power converters is proposed and an example is illustrated. The accuracy of this model is validated with experimental results performed using a 4.5 kW boost converter. This method is an efficient way to perform real time electro-thermal simulations of power electronic circuits operating at high switching frequencies.

Ion back flow(IBF) is defined as the ions that are generated during multiplication in a thick-gas-electron-multiplier (THGEM) detector flow along the electric field. In order to suppress the IBF effect, we study ion transportation for THGEMs with various high voltages and geometrical parameters. By measuring the currents of all the electrodes of the THGEMs, the effective gain and ion back flow ratio are calculated. The measurement and simulation results reveal that with a staggered triple THGEM configuration, ion back flow can be suppressed to 1% with a proper working high voltage. The gain of the staggered configuration is less than that of the aligned configuration by 5% under the same high voltage condition. The design and the results are presented.

Distribution and configuration of nucleolar DNA in the nucleolus of pea (Pisum sativum) were analyzed using cytochemical NAMA-Ur DNA specific stain method. The results showed that nucleolar DNA distributed in FC and juncture of FC/DFC in the forms of surrounding FC. rDNA in different positions existed in either condensed or uncondensed forms. Nucleolus-associated chromatin outside nucleolus extended in the periphery of FC via channels in the nucleolus.

The nuclei and chromosomes were isolated from plasmodia of Physarum polycephalum. The nuclear matrix and chromosome scaffold were obtained after the DNA and most of the proteins were extracted with DNase I and 2 M NaCl. SDS-PAGE analyses revealed that the nuclear matrix and chromosome scaffold contained a 37 kD polypeptide which is equivalent to tropomyosin in molecular weight. Immunofluorescence observations upon slide preparations labeled with anti-tropomyosin antibody showed that the nuclear matrix and chromosome scaffold emanated bright fluorescence, suggesting the presence of the antigen in them. Immunodotting results confirmed the presence of tropomyosin in the nuclear matrix and chromosome scaffold. Immunoelectron microscopic observations further demonstrated that tropomyosin was dispersively distributed in the interphase nuclei and metaphase chromosomes.