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Anisotropy is a common phenomenon in subsurface strata and should be considered in seismic imaging and inversion. Seismic imaging in a vertical transversely isotropic (VTI) medium does not take into account the effects of the tilt angles, which can lead to degraded migrated images in areas with strong anisotropy. To correct such waveform distortion, reduce related image artifacts, and improve migration resolution, a tilted transversely isotropic (TTI) least-squares reverse time migration (LSRTM) method is presented. In the LSRTM, a pure qP-wave equation is used and solved with the finite-difference method. We have analyzed the stability condition for the pure qP-wave equation using the matrix method, which is used to ensure the stability of wave propagation in the TTI medium. Based on this wave equation, we derive a corresponding demigration (Born modeling) and adjoint migration operators to implement TTI LSRTM. Numerical tests on the synthetic data show the advantages of TTI LSRTM over VTI RTM and VTI LSRTM when the recorded data contain strong effects caused by large tilt angles. Our numerical experiments illustrate that the sensitivity of the adopted TTI LSRTM to the migration velocity errors is much higher than that to the anisotropic parameters (including epsilon, delta, and tilted angle parameters), and its sensitivity to the epsilon model and tilt angle is higher than that to the delta model.

The anisotropic properties of subsurface media cause waveform distortions in seismic wave propagation, resulting in a negative influence on seismic imaging. In addition, wavefields simulated by the conventional coupled pseudo-acoustic equation are not only affected by SV-wave artifacts but are also limited by anisotropic parameters. We propose a least-squares reverse time migration (LSRTM) method based on the pure qP-wave equation in vertically transverse isotropic media. A finite difference and fast Fourier transform method, which can improve the efficiency of the numerical simulation compared to a pseudo-spectral method, is used to solve the pure qP-wave equation. We derive the corresponding demigration operator, migration operator, and gradient updating formula to implement the LSRTM. Numerical tests on the Hess model and field data confirm that the proposed method has a good correction effect for the travel time deviation caused by underground anisotropic media. Further, it significantly suppresses the migration noise, balances the imaging amplitude, and improves the imaging resolution.

The crystal structure of tungsten monocarbide (WC) is researched from 0 to 650 GPa through first principles calculations. The results verify that the experimental structure (hP2-WC) with the space group P 6¯m2 is the most stable phase in a wide range of pressure. Above 231 GPa, a new stable structure (space group P63/mmc, hP4-WC) is found to be the most stable phase, and it will transform to a CsCl-type phase (cF8-WC) around 582 GPa. Phonon calculations reveal that the hP4-WC phase is dynamically stable and may be a metastable structure at ambient conditions. The cF8-WC phase possesses dynamical stability above 20 GPa. The hP4-WC phase is a low compressible material with a large bulk modulus of 377 GPa at zero pressure. The hardness values of hP2-WC and hP4-WC at zero pressure are 32 and 21 GPa, respectively, while the cF8-WC phase possesses a hardness of 21 GPa at 20 GPa, implying that these phases are potential hard materials. The temperature–pressure phase boundary of WC is obtained by means of the quasi-harmonic approximation method. As the temperature increases, the transition pressure from hP2-WC to hP4-WC remained nearly unchanged. The transition pressure between hP4-WC and cF8-WC decreases with the increasing temperature.

It is serious harm of icing of transmission lines for power system. Deicing robots can replace manual methods, and it is the developmental tendency of transmission lines deice. Recent achievements of the deicing robot were reviewed, focusing on the research of deicing device, which provides technical reference for the design of deicer.

The structural B1–B2 (B1 is the NaCl phase and B2 is the CsCl phase) phase transition of MgS and the elastic properties of the B1 and B2 phases of MgS are investigated by ab initio plane-wave pseudopotential density functional theory method. The dependences of the elastic constants c ij , the aggregate elastic modulus B S , G , and the Debye temperature Θ D on pressure are successfully discussed. From the usual condition of equal enthalpies, we find that the structure B1–B2 phase transition of MgS occurs at 255.5 GPa. Moreover, the dependences of the aggregate elastic modulus and the Debye temperature on the pressure P have been investigated for the first time.

The elastic constants of cubic boron nitride (c–BN) are calculated by the first-principles method at ambient condition. The dependence of the elastic constants, the bulk modulus B, and the shear modulus G on the applied pressure are presented. The calculated results are in good agreement with the comparable experimental and theoretical values. The deviation from the Cauchy relation and the elastic anisotropy are investigated. The normalized elastic constants c ij ′ are introduced to investigate elasticity of c–BN in more detail. Moreover, the thermodynamic properties (Debye temperature, melting temperature) and sound velocity have been investigated under high pressure for the first time.

The equations of state (EOS) and other thermodynamic properties of cubic boron nitride (C-BN) have been studied by the first-principles method under high pressure. Under ambient conditions, our results are consistent with the available experimental data and those calculated by others. At the same time, the dependences of Young’s modulus and the shear modulus of C-BN on pressure P are successfully obtained. Moreover, the variation of the Poisson ratio, Debye temperature, specific heat, and thermal expansion coefficient with pressure P up to 200 GPa at 300 K have been investigated for the first time by means of a quasi-harmonic Debye model, in which phononic effects are considered.

The melting curve of MgSiO3 perovskite was simulated using molecular dynamics method combining with the effective pair potentials under the lower mantle conditions. It was shown that the state equation simulated for MgSiO3 perovskite is very successful in reproducing accurately the experimental data over a wide range of pressure. The pressure dependence of the simulated melting temperature of MgSiO3 perovskite is in agreement with the recent experimental data. The melting curve simulated for MgSiO3 is very steep at pressures below 60 GPa first, then it becomes smooth with increasing pressure. At the core mantle boundary pressure 135 GPa, MgSiO3 perovskite melts at 6500 K, which is significantly lower than that of the extrapolations of the experimental data from Zerr and Boehler.

The elastic constants of B1- and B2-type MgO and SrO are calculated by a first-principles method at ambient condition. For B1-type MgO and SrO, the dependence of the elastic constants, the bulk modulus B , the shear constants c S and the Cauchy relation on the applied pressure are presented. The calculated results agree quite well with the comparable experimental data and the values of other works. Moreover, the thermodynamic properties (Debye temperature, melting temperature) and sound velocity is investigated under high pressure for the first time.

The elastic constants of superconducting MgB2 are calculated using a molecular dynamics method (MD) with shell model. The lattice parameters, live independent elastic constants, equations of state (EOS), Debye temperature, and bulk modulus of MgB2,are obtained. Meanwhile, the dependence of the bulk modulus B, the lattice parameters a and c, and the unit cell volume V on the applied pressure are presented. It is demonstrated that the method introduced here can well reproduce the experimental results with a reasonable accuracy.

We present high spatial resolution X-ray spectroscopy of Tycho’s supernova remnant (SNR) using observational data from Chandra. The whole remnant was divided into 26 × 27 regions, with each of them covering 20′′ × 20′′. We selected 536 pixels with enough events to generate spectra and fit them with an absorbed two component non-equilibrium ionization model. We obtained maps of absorbing column density, weight-averaged temperature, ionization age and abundances for O, Ne, Mg, Si, S and Fe, with emission used to determine the weight. The abundance maps and the finding that Fe abundance is not correlated with any other element suggest that Fe is located at a smaller radius than other elements, supporting the onion shell model with emission from more massive elements peaking more toward the center. A tight correlation between Si and S abundances support both Si and S coming from explosive O-burning and/or incomplete Si-burning. O and Ne abundances show no correlation with any other element. Considering that O, Ne and Mg are all synthesized in the same process (C/Ne-burning), we suggest that O/Ne/Mg might mix well with other elements during the explosion of the supernova and the expansion of the SNR.

Using a first-principles noncollinear wave-function-matching method, we studied the spin-transfer torques (STTs) in CoFe/Mg-B-O/CoFe(001) magnetic tunnel junctions (MTJs), where three different types of B-doped MgO in the spacer are considered, including B atoms replacing Mg atoms (Mg$_3$BO$_4$), B atoms replacing O atoms (Mg$_4$BO$_3$), and B atoms occupying interstitial positions (Mg$_4$BO$_4$) in MgO. A strong asymmetric angular dependence of STT can be obtained both in ballistic CoFe/Mg$_3$BO$_4$ and CoFe/Mg$_4$BO$_4$ based MTJs, whereas a nearly symmetric STT curve is observed in the junctions based on CoFe/Mg$_4$BO$_3$. Furthermore, the asymmetry of the angular dependence of STT can be suppressed significantly by the disorder of B distribution. Such skewness of STTs in the CoFe/Mg-B-O/CoFe MTJs could be attributed to the interfacial resonance states induced by the B diffusion into MgO spacer. The present investigation demonstrates the feasibility of effectively enhancing microwave output power in MgO based spin torque oscillator (STO) by doping the B atoms into MgO spacer., 8 pages, 8 figures

The structural properties of Mo2Ga2C are simulated by first-principles under pressure. At 40 GPa, the axial compressibilities of [Formula: see text]- and [Formula: see text]-axes are 0.9763 and 0.9264, respectively, which are the known largest and smallest values in the [Formula: see text] compounds. A phase transition at 48 GPa is observed with an abrupt increase of [Formula: see text]-axis and a rapid decrease of [Formula: see text]-axis. The elastic properties and phonon imaginary frequencies confirmed the structural transition at 48 GPa, which probably should be the lowest-pressure transition in the [Formula: see text] ([Formula: see text], etc.) phases. The anti-expansion of Mo–Mo bond length is responsible for the [Formula: see text]-axis ultra-incompressibility as well as the structural transition at 48 GPa.

Using Vanderbilt-type plane-wave ultrasoft pseudopotentials within the generalized gradient approximation (GGA) in the frame of density functional theory (DFT), we have investigated the crystal structures, elastic, and thermodynamic properties for Ti2SC under high temperature and high pressure. The calculated pressure dependence of the lattice volume is in excellent agreement with the experimental results. The calculated structural parameter of the Ti atom experienced a subtle increase with applied pressures and the increase suspended under higher pressures. The elastic constants calculations demonstrated that the crystal lattice is still stable up to 200 GPa. Investigations on the elastic properties show that the c axis is stiffer than the a axis, which is consistent with the larger longitudinal elastic constants (C33, C11) relative to transverse ones (C44, C12, C13). Study on Poisson's ratio confirmed that the higher ionic or weaker covalent contribution in intra-atomic bonding for Ti2SC should be assumed and the nature of ionic increased with pressure. The ratio (B/G) of bulk (B) and shear (G) moduli as well as B/C44 demonstrated the brittleness of Ti2SC at ambient conditions and the brittleness decreased with pressure. Moreover, the isothermal and adiabatic bulk moduli displayed opposite temperature dependence under different pressures. Again, we observed that the Debye temperature and Gruneisen parameter show weak temperature dependence relative to the thermal expansion coefficient, entropy, and heat capacity, from which the pressure effects are clearly seen.

We investigate the elastic and the thermodynamic properties of nanolaminate V2GeC by using the ab initio pseudopotential total energy method. The axial compressibility shows that the c axis is always stiffer than the a axis. The elastic constant calculations demonstrate that the structural stability is within 0–800 GPa. The calculations of Young's and shear moduli reveal the softening behaviour at about 300 GPa. The Possion ratio makes a higher ionic or a weaker covalent contribution to intra-atomic bonding and the degree of ionicity increases with pressure. The relationship between brittleness and ductility shows that V2GeC is brittle in ambient conditions and the brittleness decreases and ductility increases with pressure. Moveover, we find that V2GeC is largely isotropic in compression and in shear, and the degree of isotropy decreases with pressure. The Gruneisen parameter, the Debye temperature and the thermal expansion coefficient are also successfully obtained for the first time.

First-principles calculations of the crystal structures, phase transition, and elastic properties of B1-B2 phase calcium sulfide (CaS) have been carried out with the plane-wave pseudopotential density functional theory method. The calculated values (for crystal structures and the phase transition) are in very good agreement with experimental data as well as with some of the existing model calculations. The dependence of the elastic constants c(ij), the aggregate elastic modulus, the deviation from the Cauchy relation, and the elastic anisotropy on pressure have been investigated. The normalized elastic constants c(ij)' have been introduced to investigate the elasticity of CaS in detail. Moreover, the variation of the Poisson ratio, Debye temperature, and longitudinal and transverse elastic wave velocity with pressure P up to 70 GPa at 0 K have been investigated for the first time.