Synthesis of Ta C and Ta_2C from tantalum and graphite in the laser-heated diamond anvil cell

The pressure dependence of the onset of the formation of Ta C and Ta2 C from the elements has been investigated by in situ X-ray diffraction and pyrometry.Ta C has been synthesized by the reaction of Ta and graphite at pressures between 8.6 and 14.3 GPa and at temperatures up to 2,300 K using a laser-heated diamond anvil cell. The products were characterized by X-ray diffraction. Ta and graphite begin to react around 1,100 K at ambient pressure conditions, and the reaction temperature increases with increasing pressure. A linear extrapolation of these data is consistent with recent observations of the formation of Ta C at 90 GPa and 3,600 K. We show that diffusion of carbon into tantalum significantly changes the lattice parameter of up to 2 % in the pressure range of up to19 GPa. In some experiments, Ta2 C was formed concomitantly. The experimentally determined bulk modulus of Ta2 C is B0;exp：= 286（5） GPa. Other tantalum carbide phases were not observed.     

Three-dimensional optical metamaterial with a negative refractive index

Metamaterials are artificially engineered structures that have properties, such as a negative refractive index, not attainable with naturally occurring materials. Negative-index metamaterials (NIMs) were first demonstrated for microwave frequencies, but it has been challenging to design NIMs for optical frequencies and they have so far been limited to optically thin samples because of significant fabrication challenges and strong energy dissipation in metals. Such thin structures are analogous to a monolayer of atoms, making it difficult to assign bulk properties such as the index of refraction. Negative refraction of surface plasmons was recently demonstrated but was confined to a two-dimensional waveguide. Three-dimensional (3D) optical metamaterials have come into focus recently, including the realization of negative refraction by using layered semiconductor metamaterials and a 3D magnetic metamaterial in the infrared frequencies; however, neither of these had a negative index of refraction. Here we report a 3D optical metamaterial having negative refractive index with a very high figure of merit of 3.5 (that is, low loss). This metamaterial is made of cascaded 'fishnet' structures, with a negative index existing over a broad spectral range. Moreover, it can readily be probed from free space, making it functional for optical devices. We construct a prism made of this optical NIM to demonstrate negative refractive index at optical frequencies, resulting unambiguously from the negative phase evolution of the wave propagating inside the metamaterial. Bulk optical metamaterials open up prospects for studies of 3D optical effects and applications associated with NIMs and zero-index materials such as reversed Doppler effect, superlenses, optical tunnelling devices, compact resonators and highly directional sources.     

Controllable Fabrication of Spider-Web-Like Structured Anaphe Panda Regenerated Silk Nanofibers/Nets via Electrospinning/Netting

An Anaphe panda silk nanofibers / nets( NFN) membrane with attractive structures consisting of common electrospun nanofibers and two-dimensional( 2D) spider-web-like structured nano-nets were successfully fabricated via electrospinning / netting technology. The unique structures of NFN membranes such as extremely small diameter( 20 nm),high porosity,large specific surface area. and biocompatibility make this Anaphe panda silk NFN membrane a promising candidate for biomedical applications. In the present study, field emission scanning electron microscopy( FESEM) was used to investigate the influence of polymer solution and humidity on nano-nets coverage and morphology. The FE-SEM images revealed that nano-net coverage area increased with increase in concentration of solution while lowering the humidity increased the nano-nets formation. Moreover,the mechanical properties of the membrane were also tested and the result showed that the silk NFN membrane displayed a breaking stress of 3. 7 MPa and breaking strain of 13. 8%. For further structural elucidation, Fourier transform infrared spectroscopy( FT-IR) was used to analyze the structural conformation changes from random coil to β-sheet in the NFN membrane which was an important factor effecting the usability of membrane. Thus,the results above confirmed the feasibility of Anaphe panda NFN structures applicability in cell tissue culture and other biomedical applications.     

A graphene-based broadband optical modulator

Integrated optical modulators with high modulation speed, small footprint and large optical bandwidth are poised to be the enabling devices for on-chip optical interconnects. Semiconductor modulators have therefore been heavily researched over the past few years. However, the device footprint of silicon-based modulators is of the order of millimetres, owing to its weak electro-optical properties. Germanium and compound semiconductors, on the other hand, face the major challenge of integration with existing silicon electronics and photonics platforms. Integrating silicon modulators with high-quality-factor optical resonators increases the modulation strength, but these devices suffer from intrinsic narrow bandwidth and require sophisticated optical design; they also have stringent fabrication requirements and limited temperature tolerances. Finding a complementary metal-oxide-semiconductor (CMOS)-compatible material with adequate modulation speed and strength has therefore become a task of not only scientific interest, but also industrial importance. Here we experimentally demonstrate a broadband, high-speed, waveguide-integrated electroabsorption modulator based on monolayer graphene. By electrically tuning the Fermi level of the graphene sheet, we demonstrate modulation of the guided light at frequencies over 1?GHz, together with a broad operation spectrum that ranges from 1.35 to 1.6?μm under ambient conditions. The high modulation efficiency of graphene results in an active device area of merely 25?μm(2), which is among the smallest to date. This graphene-based optical modulation mechanism, with combined advantages of compact footprint, low operation voltage and ultrafast modulation speed across a broad range of wavelengths, can enable novel architectures for on-chip optical communications.     

Implications of the polymorphism of HLA-G on its function,regulation, evolution and disease association

The HLA-G gene displays several peculiarities that are distinct from those of classical HLA class I genes. The unique structure of the HLA-G molecule permits a restricted peptide presentation and allows the modulation of the cells of the immune system. Although polymorphic sites may potentially influence all biological functions of HLA-G, those present at the promoter and 3′ untranslated regions have been particularly studied in experimental and pathological conditions. The relatively low polymorphism observed in the MHC-G coding region both in humans and apes may represent a strong selective pressure for invariance, whereas, in regulatory regions several lines of evidence support the role of balancing selection. Since HLA-G has immunomodulatory properties, the understanding of gene regulation and the role of polymorphic sites on gene function may permit an individualized approach for the future use of HLA-G for therapeutic purposes.