In situ thermal reduction of graphene oxide for high electrical conductivity and low percolation threshold in polyamide 6 nanocomposites

Electrically conductive and thermally stable polyamide 6 (PA 6) nanocomposites were prepared through one-step in situ polymerization of ε-caprolactam monomer in the presence of electrically insulating and thermally unstable graphene oxide (GO) nanosheets. These nanocomposites show a low percolation threshold of ∼0.41 vol.% and high electrical conductivity of ∼0.028 S/m with only ∼1.64 vol.% of GO. Thermogravimetric analysis and X-ray photoelectron spectroscopy results of GO before and after thermal treatment at the polymerization temperature indicate that GO was reduced in situ during the polymerization process. X-ray diffraction patterns and scanning electron microscopy observation confirm the exfoliation of the reduced graphene oxide (RGO) in the PA 6 matrix. The low percolation threshold and high electrical conductivity are attributed to the large aspect ratio, high specific surface area and uniform dispersion of the RGO nanosheets in the matrix. In addition, although GO has a poor thermal stability, its PA 6 nanocomposite is thermally stable with a satisfactory thermal stability similar to those of neat PA 6 and PA 6/graphene nanocomposite. Such a one-step in situ polymerization and thermal reduction method shows significant potential for the mass production of electrically conductive polymer/RGO nanocomposites.     

Preparation of metal ion (Fe and Ni) doped TiO2 nanoparticles supported on ZSM-5 zeolite and investigation of its photocatalytic activity

Metal ion doped TiO₂ nanoparticles supported on ZSM-5 zeolite (M-TiO₂/ZSM-5 composites, M = Fe or Ni) were synthesized by hydrothermal method. The prepared composites were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and UV–vis diffuse reflectance spectra (DRS). The photocatalytic activities of composites were evaluated by degradation of yellow GX aqueous solution under ambient condition. Fe-TiO₂/ZSM-5 composite showed to be more efficient catalyst for degradation of dye molecules as compared with Ni-TiO₂/ZSM-5 and TiO₂/ZSM-5. Its higher photocatalytic activity is attributed to the effective separation of charge carriers that will be discussed in this paper in detail.     

Combating Implant Infections: Shifting Focus from Bacteria to Host

The widespread use of biomaterials to support or replace body parts is increasingly threatened by the risk of implant-associated infections. In the quest for finding novel anti-infective biomaterials, there generally has been a one-sided focus on biomaterials with direct antibacterial properties, which leads to excessive use of antibacterial agents, compromised host responses, and unpredictable effectiveness in vivo. This review sheds light on how host immunomodulation, rather than only targeting bacteria, can endow biomaterials with improved anti-infective properties. How antibacterial surface treatments are at risk to be undermined by biomaterial features that dysregulate the protection normally provided by critical immune cell subsets, namely, neutrophils and macrophages, is discussed. Accordingly, how the precise modification of biomaterial surface biophysical cues, or the incorporation of immunomodulatory drug delivery systems, can render biomaterials with the necessary immune-compatible and immune-protective properties to potentiate the host defense mechanisms is reviewed. Within this context, the protective role of host defense peptides, metallic particles, quorum sensing inhibitors, and therapeutic adjuvants is discussed. The highlighted immunomodulatory strategies may lay a foundation to develop anti-infective biomaterials, while mitigating the increasing threat of antibacterial drug resistance.     

Anharmonic analysis of defective crystals with many-body interactions using symmetry reduction

In this paper we first classify and formulate various types of defects with respect to their symmetries and then show that with this general formulation, one can study the structures and energetics of defects in different crystalline materials effectively. We present all the calculations for the embedded-atom-type potentials but the formulation can, in principle, be applied for any many-body interatomic potential. As examples of defects in crystals with many-body interactions, we study point defects, free surfaces and grain boundaries in fcc Cu and grain boundaries in NiAl. We discuss free surface modelling by relaxing both a semi-infinite lattice and a slab with increasing finite thickness. We demonstrate through several numerical examples that our general framework of anharmonic lattice statics can be used for comparing different interatomic potentials in terms of the structure and energy they predict for a given defect. In the case of fcc Cu, we show how both the structures and energetics of different defects can strongly depend on the choice of potentials.     

Cobalt-based bulk glassy alloy with ultrahigh strength and soft magnetic properties

Bulk metallic glasses--formed by supercooling the liquid state of certain metallic alloys--have potentially superior mechanical properties to crystalline materials. Here, we report a Co(43)Fe(20)Ta(5.5)B(31.5) glassy alloy exhibiting ultrahigh fracture strength of 5,185 MPa, high Young's modulus of 268 GPa, high specific strength of 6.0 x 10(5) Nm kg(-1) and high specific Young's modulus of 31 x 10(6) Nm kg(-1). The strength, specific strength and specific Young's modulus are higher than previous values reported for any bulk crystalline or glassy alloys. Excellent formability is manifested by large tensile elongation of 1,400% and large reduction ratio in thickness above 90% in the supercooled liquid region. The ultrahigh-strength alloy also exhibited soft magnetic properties with extremely high permeability of 550,000. This alloy is promising as a new ultrahigh-strength material with good deformability and soft magnetic properties.     

Phase Morphology and Thermal Characteristics of Binary Blends Based on PTT and PA12

Summary Phase morphology, miscibility and thermal properties of a binary blend, poly- (trimethylene terephthalate) (PTT) / polyamide-12 (PA12), were examined and found to be immiscible showing a phase-separated morphology. DSC cooling data of the blends indicates that the melt crystallinity of PTT phase increases, with respect to pure state, upon blending with PA12 while that of polyamide phase declines in the presence of PTT phase implying that polyester molecules reduces the crystallization ability of polyamide phase. Also, PA12 in that blend where it is minor phase shows a fractionated crystallization. A significant cold crystallization exotherm supposed to be due to the reorganization of polymeric chains was exhibited by PTT phase in DSC second heating thermograms which its degree was raised upon blending with PA12. DMA graphs reveal a single tan peak due to the fact that the glass transition of the respective constituents overlap and a single peak comes into view. Therefore, DMA can not be solely used to assess the miscibility in this system.     

Deformation induced transformations and grain boundary thickness in nanocrystalline B2 FeAl

Precise measurement of fundamental Bragg peak shifts during milling of nanocrystalline ordered B2 Fe₆₀Al₄₀ has allowed for the first time, the deconvolution of the 110 fundamental Bragg peak intensities of the b.c.c. disordered regions and of the ordered B2 regions from the start and before full disappearance of the latter. The evolution of the lattice parameter a₀ of the b.c.c. solid solution with milling time shows two characteristics. First a jump to higher values from the initial a₀ of the B2 phase, with a Δa₀ change of the order of 1% corresponding to a volume per atom ΔV_expansion of about 3%. Subsequently, a₀ continues to increase slowly with further milling at constant grain size D and in the absence of any B2 phase. This continuing change of a₀ with further milling up to at least 180 min is attributable to a reduction of chemical short-range order (CSRO) or the number of Al–Fe heteroatomic “bonds”. The appearance of two well-defined maxima in the hyperfine field (HF) distributions derived from the Mössbauer spectra indicated the presence of two ferromagnetic environments contributing to the broadened Mössbauer resonance sextet signal. The evolution of the second component of this Mössbauer signal scales with the grain size. Using the mean grain size D derived from X-ray peak profiles and TEM pictures together with the grain boundary thickness d_gb of 1.25 nm determined by Fultz et al. (J. appl. Phys., 1996, 7, 127) for b.c.c. Fe-based alloys, the fraction of grain boundary atoms n_gb/n_total was estimated and found to be consistent with the fraction of Fe atoms contributing to the lower HF component of the Mössbauer sextet signal. The grain boundary atom count using both methods confirms that grain boundaries in materials nanocrystallized by heavy deformation are nearly as dense as in the bulk.     

The fourth mode of fracture in fractal fracture mechanics

This paper offers a systematic approach for obtaining the order of stress singularity for different self-similar and self-affine fractal cracks. Mode II and Mode III fractal cracks are studied and are shown to introduce the same order of stress singularity as Mode I fractal cracks do. In addition to these three classical modes, a Mode IV is discovered, which is a consequence of the fractal fracture. It is shown that, for this mode, stress has a weaker singularity than it does in the classical modes of fracture when self-affine fractal cracks are considered, and stress has the same order of singularity when self-similar cracks are considered. Considering this new mode of fracture, some single-mode problems of classical fracture mechanics could be mixed-mode problems in fractal fracture mechanics. By imposing a continuous transition from fractal to classical stress and displacement fields, the complete forms of the stress and displacement fields around the tip of a fractal crack are found. Then a universal relationship between fractal and classical stress intensity factors is derived. It is demonstrated that for a Mode IV fractal crack, only one of the stress components is singular; the other stress components are identically zero. Finally, stress singularity for three-dimensional bodies with self-affine fractal cracks is studied. As in the two-dimensional case, the fourth mode of fracture introduces a weaker stress singularity for self-affine fractal cracks than classical modes of fracture do.     

Local atomic structure of Zr–Cu and Zr–Cu–Al amorphous alloys investigated by EXAFS method

We report on extended X-ray absorption fine structure (EXAFS) study of rapidly quenched Zr–Cu and Zr–Cu–Al glassy alloys. The local atomic order around Zr and Cu atoms was investigated. From the EXAFS data fitting the values of coordination number, interatomic distances and mean square atomic displacement were obtained for wide range of compositions. It was found that icosahedral symmetry rather than that of corresponding crystalline analogs dominates in the local atomic structure of Zr–Cu and Zr–Cu–Al amorphous alloys. Judging from bonding preferences we conclude that addition of Al as an alloying element results in considerable deviation from random mixing behavior observed in binary Zr–Cu alloys.     

A single-stage operational amplifier with enhanced transconductance and slew rate for switched-capacitor circuits

The DVB-T2 standard for digital terrestrial broadcasting supports the use of quadrature amplitude modulation constellations where the constellation points are rotated in the I–Q plane. This combined with a cyclic delay of the Q component provides improved performance in some fading channels. The complexity of the optimal demapping process for rotated constellations is however significantly higher than for non-rotated constellations. This makes the DVB-T2 demapper one of the most computationally complex parts of a receiver. In this article, we examine possible simplifications of the demapping process suitable for implementation on a general purpose computer containing a modern graphics processing unit (GPU). Furthermore, we measure the performance in terms of throughput, as well as accuracy, of the implemented algorithms. The implementations are designed to interface efficiently to a previously implemented real-time capable GPU-based low-density parity-check channel decoder.