Analysis of one ambient seismic noise in Tianjin

During checking continuous waveform record, it was found that some stations of Tianjin such as EWZ were significantly affected by one unknown noise, and EWZ station was the most seriously affected. Long term observations had also found that this noise cannot be observed for uncertainly several days each year. This noise was all year round and did not change with day and night time, and it had been existed for many years. This noise was different from typical environmental background noise and had some fixed characteristics. This article studied the noise from several aspects such as its own characteristic, its coverage of influence, spectral characteristics, and impact on earthquake records. The research has shown that the noise was not affected by natural factors such as weather and season, and had a characteristic of amplitude decreasing as the distance increasing from EWZ station. The main frequency of this noise ranged 1～2 Hz. The impact of noise was relatively wide and it can be recorded by 12 surrounding stations, with YGZ station being the farthest and approximately 58 km away from EWZ station. Through polarization analysis, it was found that the propagation of noise had a specific directionality, so it is preliminary judged that this noise had the characteristic of fixed source noise. This noise will have an impact on seismic records, reducing the seismic phase pickup rate, and even completely submerging it in the noise. Frequency filtering can improve it

Wear Behaviors of a Ti-Based Bulk Metallic Glass at Elevated Temperatures

Bulk metallic glasses (BMGs) often offer excellent physical, chemical, and mechanical properties such as high strength, high hardness, and good wear/corrosion resistance, stemming from their unique atomic configuration. These properties enable them to be a potential engineering material in a range of industrial applications. However, the wear behaviors must be considered in structural applications. Here, the wear tests of a TiZrNiCuBe bulk metallic glass at high temperatures were carried out. As the testing temperature increases, the wear rate of the studied BMG sample gradually decreases and the sample surface becomes smoother. Meanwhile, a higher applied normal load causes a higher wear rate. The wear mechanism evolves from the abrasive to adhesive mode with increase in the testing temperature. The results obtained here could shed more insights into the deformation mechanism of BMGs and thus extend their industrial uses in high-temperature environments

Magnetically Tuned Continuous Transition from Weak to Strong Coupling in Terahertz Magnon Polaritons

Depending on the relative rates of coupling and dissipation, a light-matter coupled system is either in the weak- or strong-coupling regime. Here, we present a unique system where the coupling rate continuously increases with an externally applied magnetic field while the dissipation rate remains constant, allowing us to monitor a weak-to-strong coupling transition as a function of magnetic field. We observed a Rabi splitting of a terahertz magnon mode in yttrium orthoferrite above a threshold magnetic field of ~ 14 T. Based on a microscopic theoretical model, we show that with increasing magnetic field the magnons transition into magnon polaritons through an exceptional point, which will open up new opportunities for in situ control of non-Hermitian systems

Microstructure and mechanical properties of a multilayered CoCrNi/Ti coating with varying crystal structure

Medium entropy alloys (MEAs), such as CoCrNi, have been demonstrated to combine high hardness and excellent ductility, thereby outperforming many high entropy alloys reported to date. In this study, a multilayered CoCrNi/Ti coating was deposited onto a M2 steel substrate using a DC magnetron sputtering system. Columnar grains can be observed in both the CoCrNi and Ti layers. A high density of periodic twin boundaries, aligned in a direction normal to the growth direction, was also observed within the columnar CoCrNi grains. Moreover, different crystal structures were identified for different CoCrNi layers. The outermost CoCrNi layer exhibited a FCC structure, whilst in contrast, both the middle and bottom CoCrNi layers exhibited a BCC structure. It was assumed that Shockley partial dislocations were responsible for the FCC to BCC transition occurring in both the bottom and middle CoCrNi layers. A high hardness of ~7.6 GPa and elastic modulus of ~233 GPa were determined for this multilayered coating by nanoindentation testing. Further, extraordinary damage tolerance was found in the multilayered CoCrNi/Ti coating under indentation loading. The steady shear banding behaviour during deformation may benefit energy dissipation and promote structural plasticity

The microstructure and mechanical properties of thin film Ni(Ti) nanocomposite coatings containing both oxygen and nitrogen

Thin film Ni(Ti) nanocomposite coatings, containing both oxygen and nitrogen, were deposited onto tool steel substrates using a reactive DC magnetron sputtering system at room temperature. A NiTi alloy target (Ni/Ti = 80/20 at.%) was used during deposition. The evolution of the microstructure of these coatings under varying N2 gas flow rate was studied by focused ion beam microscopy and transmission electron microscopy. A clear structural change, from columnar grains to very fine equiaxed grains with a considerable level of porosity, was evidenced. X-ray diffraction, together with X-ray photoelectron spectroscopy, was employed to determine the crystal structure and composition of these coatings. Analysis of these data revealed that the nanocomposite coatings were composed of a Ni matrix with nanocrystalline TiN, embedded together with amorphous TiO2. Nanoindentation results demonstrated that Ni dissolved with ~ 15 at.% Ti solid solution possesses higher values of elastic modulus, hardness and better resistance to both elastic and plastic deformation than the Ni(Ti) nanocomposite coatings containing higher concentrations of both nitrogen and oxygen. The presence of porosity in the nanocomposite coatings was expected to worsen the mechanical properties of these coatings, while the amorphous TiO2 phase may help facilitate grain boundary motion. © 2016 Elsevier B.V

Combination of GPS, HY-2A and COSMIC observations to establish global ionospheric map

1000-1010The systematic biases of the HY-2A altimetry satellite observations and COSMIC observations between ground-based GNSS observations are taken into account, and they were estimated together with the unknown coefficients of SH expansion by least squares. Meanwhile, Helmert variance component estimation method was used to determine the precise weights of each observations taking into account of the different accuracy of each observations. As an example, three types of observations in DOY 101, 2015 were used to establish a combined GIM in two-hourly snapshots. The differences of the combined GIM and GIM published by IGS were also analyzed. Compared with the RMS map of GIM published by IGS, it found that the accuracy of the combined GIM improved about 0.3TECU after adding HY-2A altimetry satellite and COSMIC observations. The accuracy improved more obvious in the ocean areas where HY-2A altimetry satellite observed

Medium entropy alloy CoCrNi coatings: Enhancing hardness and damage-tolerance through a nanotwinned structuring

Medium entropy alloys (MEA) are defined as alloys consisting of three equiatomic elements, such as CoCrNi. MEAs are reported to have superior mechanical properties and high thermodynamic stability, as well as excellent fracture toughness at cryogenic temperatures. Here, we investigate a series of equiatomic medium entropy alloy coatings, containing three elements, Co, Cr, Ni. These coatings were deposited onto M2 steel substrates with a range of coating thicknesses using a DC magnetron sputtering system using a CoCrNi alloy target (1:1:1 at.%). The microstructure and mechanical properties were examined by a number of characterization techniques, including X-ray diffraction (XRD), transmission electron microscopy (TEM) and nanoindentation. XRD analysis showed that the coatings were dominated by a fcc CoCrNi phase, with a smaller amount of hcp Co. TEM analysis demonstrated that the elongated grains contained a high density of {111} nanotwins. In addition, the residual stresses in the coatings were analysed using X-ray diffraction by adopting the conventional sin2ψ method. A high hardness value, ~ 10 GPa, was determined by nanoindentation of these coatings. Exceptional damage-tolerance was also found in these coatings under contact loading. It is believed that the nanotwinned structure is responsible for the high hardness and damage tolerance observed in the new coatings

Microstructure and properties of transition metal nitride and medium entropy alloy coatings

Hard thin film coatings play an important role in many industrial applications, such as cutting tools and biomedical devices. Magnetron sputtering, as one important deposition method, has been widely applied to a wide range of coating types. In this thesis, the microstructure and mechanical properties of a number of different families of coatings, deposited by magnetron sputtering, were investigated in detail. First, the influence of reactive gas ratio on the microstructure and mechanical properties of Ni-Ti-O-N nanocomposite coatings was studied. It was shown that an increase in reactive gas flow ratio resulted in a transformation from a dense structure with columnar grains into a porous structure with equiaxed grains, accompanied by a degradation in mechanical properties. It was shown that intergranular porosity had a detrimental effect on both hardness and elastic modulus. Further, the effect of substrate bias on the TiAlSiN coatings deposited at ~ 500°C was investigated. Variations in substrate bias had little impact on the chemical concentration of the coatings, but significantly influenced the microstructure, phase composition and mechanical properties. An evolution of microstructure from coarse to fine columnar grains with increasing bias voltage was identified, together with enhanced hardness and elastic modulus. Further, a transformation from a mixed fcc TiN + fcc AlN phases into a single fcc TiAlN phase was observed with increasing substrate bias. Finally, a series of equiatomic medium entropy alloy CoCrNi coatings, including both monolayer coatings and a tri-layered CoCrNi/Ti coating, was deposited onto M2 substrates. It was found that the monolayer CoCrNi coatings were composed of mostly a fcc CoCrNi phase, together with a small amount of a hcp Co-based phase. Interestingly, for the tri-layered coating, the outmost layer exhibited a fcc structure, while a bcc structure was observed in both the bottom and middle layers. The transition from fcc to bcc phase may be explained by Shockley partial dislocation motion under compressive stress. A remarkable hardness of ~10 GPa was determined for these coatings. The presence of nanotwins in these coating may account for the high hardness and toughness

Tests on the Accuracy and Scalability of the Full-Potential DFT Method Based on Multiple Scattering Theory

We investigate a reduced scaling full-potential DFT method based on the multiple scattering theory (MST) code MuST, which is released online (https://github.com/mstsuite/MuST) very recently. First, we test the accuracy by calculating structural properties of typical body-centered cubic (BCC) metals (V, Nb, and Mo). It is shown that the calculated lattice parameters, bulk moduli, and elastic constants agree with those obtained from the VASP, WIEN2k, EMTO, and Elk codes. Second, we test the locally self-consistent multiple scattering (LSMS) mode, which achieves reduced scaling by neglecting the multiple scattering processes beyond a cut-off radius. In the case of Nb, the accuracy of 0.5 mRy/atom can be achieved with a cut-off radius of 20 Bohr, even when small deformations are imposed on the lattice. Despite that the calculation of valence states based on MST exhibits linear scaling, the whole computational procedure has an overall scaling of about O(N-1.6), due to the fact that the updating of Coulomb potential scales almost as O(N-2). Nevertheless, it can be still expected that MuST would provide a reliable and accessible way to large-scale first-principles simulations of metals and alloys