Molecular dynamics simulation of phonon thermal transport in nanotwinned diamond with a new optimized Tersoff potential.

The inaccuracy of the most widely used potentials in calculating the phonon transport of sp3 carbon materials hinders the use of molecular dynamics simulations for revealing the underlying mechanism of phonon transport in diamond and related materials. Here, we introduce an optimized Tersoff potential by optimizing the parameters to fit the experimentally determined phonon dispersion in diamond along the high-symmetry directions. Molecular dynamics simulations are performed using this new potential to investigate the phonon thermal transport in flawless and nanotwinned diamond. The simulation results show that while the phonon lifetimes of nanotwinned diamond are slightly lower than those of the flawless one, the phonon group velocities of nanotwinned diamond are obviously lower than those of diamond. The present results indicate that the twin boundaries in diamond are ineffective in scattering the phonons and the lower thermal conductivity of the nanotwinned diamond mainly originates from the lower group velocities due to its reduced structural rigidity.

Ultrabroad Band Microwave Absorption of Carbonized Waxberry with Hierarchical Structure.

Developing microwave absorption materials with broadband and lightweight characters is of great significance. However, it is still a great challenge for carbonized biomass without loading magnetic particles to cover the broad microwave frequency. Herein, it is proposed to carbonize freeze-dried waxberry to make full use of its natural hierarchical gradient structure to target the ultrabroad band microwave absorption. The carbonized freeze-dried waxberry shows radial-gradient and hierarchical structure. The different components of hierarchical waxberry demonstrate gradient dielectric properties: the outer component shows anisotropic dielectric constants with smaller value, while the inner core shows higher dielectric constants. This gradient dielectric property is beneficial to the impedance matching and strong polarization. As a result, the bandwidth of carbonized waxberry exhibits an ultrabroad band microwave absorption, ranging from 1 to 40 GHz with the reflection loss value below -8 dB. Meanwhile, the bandwidth can cover from 8 to 40 GHz when the reflection loss is below -15 dB. The ultrabroad microwave absorption is attributed to the hierarchical radial-gradient structure of carbonized waxberry, which provides good impedance matching with air media. This achievement paves the way for the exploitation of natural hierarchical biomass as a superlight and broadband high-performance microwave absorption material.

Manipulation and formation mechanism of silica one-dimensional periodic structures by roller electrospinning.

A roller electrospinning technique is combined with sol-gel chemistry to fabricate silica and polymeric materials on conductive and nonconductive substrates to verify its ability for controlling the long-range periodic structure of the final product. According to the experimental results, formation of the one-dimensional periodic silica structure was dependent on the electrical conductivity of the collector substrate. The periodic density seems to be related to the width of silica product. No effect from the electrical conductivity of collector substrate on the structure of polymeric system was observed. An energy transformation model was proposed to investigate the formation mechanism of this periodic structure. The theoretical simulation indicates that large width-to-thickness ratio of the product and high-energy transformation efficiency favor the formation of the long-range periodic structure.

Simulation of Four-Point Bending Fracture Test of Steel-Fiber-Reinforced Concrete.

To investigate the influence of addition amount and length of steel fibers on the bearing capacity of a concrete beam, this study simulated the crack propagation process of a concrete beam in a four-point bending experiment. The extended finite element method (XFEM) using the ABAQUS software was adopted. Additionally, stress distribution trends for the concrete under loading and load-displacement curves at the stressed points were obtained. The simulation results for a concrete beam with different amounts and lengths of steel fibers were compared and analyzed, and conclusions were drawn. The experiment shows that the flexural performance of the concrete improves with increases in the length and amount of steel fibers, but the reinforcement effects produced by different amounts and lengths of steel fibers are different. When the steel fiber content is 1.5% and the length is 20-25 mm, the reinforcement effect in the concrete is significantly improved, and its flexural strength is nearly doubled.

Twin-Structured Graphene Metamaterials with Anomalous Mechanical Properties.

Typically, solid materials exhibit transverse contraction in response to stretching in the orthogonal direction and transverse expansion under compression conditions. However, when flexible graphene nanosheets are assembled into a 3D porous architecture, the orientation-arrangement-delivered directional deformation of micro-nanosheets may induce anomalous mechanical properties. In this study, a 3D hierarchical graphene metamaterial (GTM) with twin-structured morphologies is assembled by manipulating the temperature gradient for ice growth during in situ freeze-casting procedures. GTM demonstrates anomalous anisotropic compression performance with programable Poisson's ratios (PRs) and improved mechanical properties (e.g., elasticity, strength, modulus, and fatigue resistance) along different directions. Owing to the designed three-phase deformation of 2D graphene sheets as basic microelements, the twin-structure GTM delivers distinctive characteristics of compressive curves with an apparent stress plateau, and follows a strengthening tendency. This multiscale deformation behavior facilitates the enhancement of energy loss coefficient. In addition, a finite element theory based numerical model is established to optimize the structural design, and validate the multiscale tunable PR mechanism and oriented structural evolution. The mechanical and thermal applications of GTM indicate that the rational manipulation-driven design of meta-structures paves the way for exploring graphene-based multifunctional materials with anomalous properties.

Identification of a five-gene signature in association with overall survival for hepatocellular carcinoma.

BACKGROUND: Hepatocellular carcinoma (HCC) is considered to be a malignant tumor with a high incidence and a high mortality. Accurate prognostic models are urgently needed. The present study was aimed at screening the critical genes for prognosis of HCC. METHODS: The GSE25097, GSE14520, GSE36376 and GSE76427 datasets were obtained from Gene Expression Omnibus (GEO). We used GEO2R to screen differentially expressed genes (DEGs). A protein-protein interaction network of the DEGs was constructed by Cytoscape in order to find hub genes by module analysis. The Metascape was performed to discover biological functions and pathway enrichment of DEGs. MCODE components were calculated to construct a module complex of DEGs. Then, gene set enrichment analysis (GSEA) was used for gene enrichment analysis. ONCOMINE was employed to assess the mRNA expression levels of key genes in HCC, and the survival analysis was conducted using the array from The Cancer Genome Atlas (TCGA) of HCC. Then, the LASSO Cox regression model was performed to establish and identify the prognostic gene signature. We validated the prognostic value of the gene signature in the TCGA cohort. RESULTS: We screened out 10 hub genes which were all up-regulated in HCC tissue. They mainly enrich in mitotic cell cycle process. The GSEA results showed that these data sets had good enrichment score and significance in the cell cycle pathway. Each candidate gene may be an indicator of prognostic factors in the development of HCC. However, hub genes expression was weekly associated with overall survival in HCC patients. LASSO Cox regression analysis validated a five-gene signature (including CDC20, CCNB2, NCAPG, ASPM and NUSAP1). These results suggest that five-gene signature model may provide clues for clinical prognostic biomarker of HCC.

Anisotropic Electromagnetic Absorption of Aligned Ti3C2Tx MXene/Gelatin Nanocomposite Aerogels.

Assembling Ti3C2Tx MXene nanosheets into three-dimensional (3D) architecture with controllable alignment is of great importance for electromagnetic wave absorption (EMA) application. However, it is a great challenge to realize it due to the weak van der Waals interconnection between MXene nanosheets. Herein, we propose to introduce gelatin molecules as a "chemical glue" to fabricate the 3D Mxene@gelatin (M@G) nanocomposite aerogel using a unidirectional freeze casting method. The Ti3C2Tx MXene nanosheets are well aligned in the M@G nanocomposite aerogel, yielding much enhanced yet anisotropic mechanical properties. Due to the unidirectional aligned microstructure, the M@G nanocomposite aerogel shows significantly anisotropic EMA properties. M@G-45 shows a -59.5 dB minimum reflection loss (RLmin) at 14.04 GHz together with a 6.24 GHz effective absorption bandwidth in the parallel direction (relative to the direction of unidirectional freeze casting). However, in the vertical direction of the same M@G aerogel, RLmin is shifted to a much lower frequency (4.08 GHz) and the effective absorption bandwidth decreases to 0.86 GHz. The anisotropic electromagnetic energy dissipation mechanism was deeply investigated, and the impendence match plays a critical role for electromagnetic wave penetration. Our lightweight M@G nanocomposite aerogel with controllable MXene alignment is very promising in EMA application.

Artificial muscle with reversible and controllable deformation based on stiffness-variable carbon nanotube spring-like nanocomposite yarn.

Carbon nanotube yarn actuators are in great demand for flexible devices or intelligent applications. Artificial muscles based on carbon nanotube yarn have achieved great progress over past decades. However, uncontrollable, small deformations and relatively slow deformation recovery are still great challenges for carbon nanotube yarn artificial muscles. Here we propose an artificial muscle based on a stiffness-variable carbon nanotube spring-like nanocomposite yarn. This nanocomposite yarn can be fabricated as artificial muscles by directly inflating epoxy resin on spring-like carbon nanotube yarn, and it shows a rapid response, and reversible and controllable deformation. The driving mechanism of the nanocomposite yarn artificial muscle is based on the change in the resin modulus controlled by Joule heat. This novel nanocomposite yarn artificial muscle can work at low voltages (≤0.8 V), and the whole reversible driving process is completed within 5 seconds (the deformation recovery process is about 2 seconds). The strain of the nanocomposite yarn artificial muscle is controlled by applied voltages, and the maximum strain can reach more than 12%. The novel nanocomposite yarn artificial muscle can produce output forces more than 20 times higher than human skeletal muscle. This CNT nanocomposite yarn artificial muscle with a spiral structure shows potential applications for actuators, sensors and micro robots.

The Out-of-Plane Compression Behavior of Cross-Ply AS4/PEEK Thermoplastic Composite Laminates at High Strain Rates.

The dynamic mechanical behavior of thermoplastic composites over a wide range of strain rates has become an important research topic for extreme environmental survivability in the fields of military protection, aircraft safety, and aerospace engineering. However, the dynamic compression response in the out-of-plane direction, which is one of the most important loading conditions resulting in the damage of composite materials, has not been investigated thoroughly when compared to in-plane compression and tensile behavior under high strain rates. Thus, we used split Hopkinson pressure bar (SHPB) tests to conduct the out-of-plane compression test of cross-ply carbon fiber-reinforced polyetheretherketone (AS4/PEEK) composite laminates. Afterward, the damage mechanism under different strain rates was characterized by the macrostructure morphologies and scanning electron microscope micrographs. Two major cases of the incomplete failure condition and complete failure condition were discussed. Dynamic stress-strain curves expound the strain rates dependencies of elastic modulus, failure strength, and failure strain. An obvious spring-back process could be observed under incomplete failure tests. For the complete failure tests, secondary loading could be observed by reconstructing and comparing the dynamic response history. Lastly, various failure modes that occurred in different loading strain rates illustrate that the damage mechanism also shows obvious strain rate sensitivity.

Stiff, Thermally Stable and Highly Anisotropic Wood-Derived Carbon Composite Monoliths for Electromagnetic Interference Shielding.

Electromagnetic interference (EMI) shielding materials for electronic devices in aviation and aerospace not only need lightweight and high shielding effectiveness, but also should withstand harsh environments. Traditional EMI shielding materials often show heavy weight, poor thermal stability, short lifetime, poor tolerance to chemicals, and are hard-to-manufacture. Searching for high-efficiency EMI shielding materials overcoming the above weaknesses is still a great challenge. Herein, inspired by the unique structure of natural wood, lightweight and highly anisotropic wood-derived carbon composite EMI shielding materials have been prepared which possess not only high EMI shielding performance and mechanical stable characteristics, but also possess thermally stable properties, outperforming those metals, conductive polymers, and their composites. The newly developed low-cost materials are promising for specific applications in aerospace electronic devices, especially regarding extreme temperatures.

Superlight, Mechanically Flexible, Thermally Superinsulating, and Antifrosting Anisotropic Nanocomposite Foam Based on Hierarchical Graphene Oxide Assembly.

Lightweight, high-performance, thermally insulating, and antifrosting porous materials are in increasing demand to improve energy efficiency in many fields, such as aerospace and wearable devices. However, traditional thermally insulating materials (porous ceramics, polymer-based sponges) could not simultaneously meet these demands. Here, we propose a hierarchical assembly strategy for producing nanocomposite foams with lightweight, mechanically flexible, superinsulating, and antifrosting properties. The nanocomposite foams consist of a highly anisotropic reduced graphene oxide/polyimide (abbreviated as rGO/PI) network and hollow graphene oxide microspheres. The hierarchical nanocomposite foams are ultralight (density of 9.2 mg·cm-3) and exhibit ultralow thermal conductivity of 9 mW·m-1·K-1, which is about a third that of traditional polymer-based insulating materials. Meanwhile, the nanocomposite foams show excellent icephobic performance. Our results show that hierarchical nanocomposite foams have promising applications in aerospace, wearable devices, refrigerators, and liquid nitrogen/oxygen transportation.