[en] The scanning-tunneling-microscopy (STM) images of xenon atoms adsorbed on a monolayer graphite sheet are calculated using the first-principles total-energy electronic structure calculations within the density functional theory (DFT) in the local density approximation (LDA). The results obtained agree well with the observations. The optimal site of adsorbed Xe atom is at the top of the center of the carbon hexagon and its equilibrium distance from monolayer graphite surface is about 3.60 A. The hybridization of C 2p electronic states (π-electronic states) and Xe 5p and 6s electronic states is the main origin of the Fermi-level local density of state (LDOS) rendering Xe atoms visible in the STM experiment

[en] We employ a finite-difference pseudopotential density-functional theory in real space and Langevin molecular dynamics annealing technique (PDFMD) to determine the ground state structures of sulfur cluster S₈, and apply a linear response method within the adiabatic time-dependent density-functional theory (TDDFT) and the local density approximation (TDLDA) to calculate optical absorption spectra. It is found that the ground state structure of sulfur cluster S₈ belongs to a crown-shaped D_4d symmetry structure and the calculated spectra exhibit a variety of features that can be used for comparison against future experimental investigations

[en] A finite-difference pseudopotential density-functional theory in real space and Langevin molecular dynamics annealing technique are applied to determine the ground state structure of sulfur cluster S₇ and the corresponding optical absorption spectra from a linear response method within the adiabatic time-dependent local density approximation. It is found that the ground state structure of sulfur cluster S₇ belongs to a chair structure with C_s symmetry and the calculated spectra exhibit a variety of features that can be used for comparison against future experimental investigations

[en] Objective: To characterize the feasibility, key technology, indications and clinical outcome of percutaneous lumbar interbody fusion. Methods: Clinical data from 32 cases [16 male, 16 female, age range 31-77 years, average disease duration (5.0±2.0) years] underwent percutaneous nucleotomy and endplate curettage was retrospectively analyzed. After percutaneous nucleotomy and endplate curettage, one expandable spinal spacer B-twin was introduced into the intervertebral space and some allograft cancellous bone implanted around the B-twin. Indications for treatment included degenerative lumbar disc herniation (LDH) with intervertebral distability or I degree spondylolisthesis (21 cases), LDH with intervertebral space collapse (10 cases) and lumbar discogenic pain (1 case). The symptoms and function of all patients were evaluated before, 3 months and 12 months after the operation by clinical outcome judgment criterion of surgical treatment for low back pain formulated by JOA, and the rate of clinical improvement and treatment efficacy were calculated. The JOA scales preoperatively, postoperatively and on the final follow-up was compared using ANOVA in SPSS. The changes before and after surgery with the JOA score and the the rate of clinical improvement between 3 months and 12 months after the operation was also compared using χ² test. Results: The average operation time 1 hour and blood loss < 20 ml, Surgical site: L3-4 4 cases, L4-5 19 cases, L5-S1 6 cases, L3-4 and L4-5 3 cases, B-Twin were implanted fusion cage 35, in three cases of intervertebral space with two implants. Average in Hospital time was (10.0±2.1) d. Complication included 1 case with displacement and 1 case with secondary instability of next intervertebral space. All the patients were evaluated after a follow-up of 3-36 months (average 13 months) 32 cases of patients with low back pain JOA score: before surgery is (4.1±1.8), 3 months after surgery, is (11.9±3.9), 1 year after surgery of the 22 cases is (12.0±3.2). Score before and after surgery were statistically significant differences (F=5.67, P<0.01). The rate of clinical improvement after surgery there was no significant difference (F=4.18, P>0.05). Conclusions: Percutaneous posterior lumbar interbody fusion with B-twin expandable fusion cage could lead to satisfactory outcome in the treatment of degenerative disc disease and intervertebral instability, which minimize surgical soft tissue and trauma spinal damage, does not destroy the structure of spinal stability. The long-term outcome, complications and fusion rate need further observing. (authors)

[en] We have investigated the structural and elastic properties of MgB₂ under high pressures using the full-potential linearized muffin-tin orbital (FP-LMTO) scheme within the generalized gradient approximation correction (GGA) in the frame of density functional theory. The calculated pressure dependence of the normalized volume is in excellent agreement with the experimental results. At the same time the elastic constants and acoustic anisotropy as a function of applied pressure are presented. Through the quasi-harmonic Debye model, we also investigate the thermodynamic properties of MgB₂.

[en] The elastic constants of superconducting MgB₂ are calculated using a molecular dynamics method (MD) with shell model. The lattice parameters, five 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.

[en] Using ab initio plane-wave pseudopotential density functional theory method, we have studied the structural and thermodynamic properties of the wurtzite boron nitride (w-BN). Through the quasi-harmonic Debye model, in which the phononic effects are considered, the dependencies of the normalized lattice parameters a/a₀ and c/c₀, the axial ratio c/a, and the normalized primitive cell volume V/V₀ on pressure P and temperature T are investigated. Furthermore, the Debye temperature Θ, the variation of thermal expansion α, as well as the heat capacity C_V as functions of P and T are studied systematically.

[en] In this paper the elastic and thermodynamic properties of the cubic zinc-blende structure BeS at different pressures and temperatures are investigated by using ab initio plane-wave pseudopotential density functional theory method within the generalized gradient approximation (GGA). The calculated results are in excellent agreement with the available experimental data and other theoretical results. It is found that the zinc-blende structure BeS should be unstable above 60GPa. The thermodynamic properties of the zinc-blende structure BeS are predicted by using the quasi-harmonic Debye model. The pressure-volume-temperature (P - V - T) relationship, the variations of the thermal expansion coefficient α and the heat capacity C_v with pressure P and temperature T, as well as the Grüneisen parameter-pressure-temperature (γ - P - T) relationship are obtained systematically in the ranges of 0-90GPa and 0-2000K

[en] The phase transition of SrS from NaCl structure (B1) to CsCl structure (B2) is investigated by means of ab initio plane-wave pseudopotential density functional theory, and the thermodynamic properties of the B1 and the B2 structures are obtained through the quasi-harmonic Debye model. It is found that the transition phase from the B1 to the B2 structures occurs at 17.9 GPa, which is in good agreement with experimental data and other calculated results. Moreover, the thermodynamic properties (including specific heat capacity, the Debye temperature, thermal expansion and Grüneisen parameter) have also been obtained successfully

[en] This paper studies the chaotic behaviours of the fractional-order unified chaotic system. Based on the approximation method in frequency domain, it proposes an electronic circuit model of tree shape to realize the fractional-order operator. According to the tree shape model, an electronic circuit is designed to realize the 2.7-order unified chaotic system. Numerical simulations and circuit experiments have verified the existence of chaos in the fraction-order unified system