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Making use of quasar spectra from LAMOST, in the spectral data around the Mg ii emission lines, research described in this paper has detected 217 Mg ii narrow absorption lines (NALs) with W r λ 2796 ≥ 3 σ w and W r λ 2803 ≥ 2 σ w in a redshift range of 0.4554 ≤ z abs ≤ 2.1110. For quasars observed by both LAMOST and SDSS, we find that 135 Mg ii NALs were obviously observed in the LAMOST spectra, 347 Mg ii NALs were were apparent in the SDSS spectra, and 132 Mg ii NALs were clearly present in both the SDSS and LAMOST spectra. The missed Mg ii NALs are likely ascribed to low signal-to-noise ratios of corresponding spectra. Among the Mg ii NALs obviously observed in SDSS or LAMOST spectra, eight Mg ii NALs were significantly changed with | Δ W r λ 2796 | ≥ 3 σ w in time intervals of Δ MJD/(1 + z em) = 359 – 2819 d.

A Gaussian type spin-polarized electronic wave packet is constructed to investigate the spin transport behaviour in an infinite two-dimensional electron gas system with Rashba spin-orbit (SO) interaction by solving the Schrodinger equation exactly. In the presence of Rashba SO interaction, the spin-dependent force induces a momentum dependent splitting of the two spin directions, the average spin current indicates the corresponding spin accumulation clearly. Furthermore, the coherence of the injected spin-polarized wave packet, as well as the transverse force, decays during the motion in the Rashba SO regime.

The properties of a carbon nanotube are dependent on its atomic structure. The atomic structure of a carbon nanotube can be defined by specifying its chiral indices, (u, v), that specify its perimeter vector (chiral vector), with which the diameter and helicity are also determined. The fine electron beam available in a modern transmission electron microscope (TEM) offers a unique probe to reveal the atomic structure of individual nanotubes.This review covers two aspects related to the use of the electron probe in the TEM for the study of carbon nanotubes: (a) to understand the electron diffraction phenomena for inter-pretation of the electron diffraction patterns of carbon nanotubes and (b) to obtain the chiral indices, (u, v), of the carbon nanotubes from the electron diffraction patterns.For a nanotube of a given structure, the electron scattering amplitude from the carbon nanotube is first described analytically in closed form using the helical diffraction theory. From a known structure as given by the chiral indices (u, v), its electron diffraction pattern can be calculated and understood.The reverse problem, i.e. assignment of the chiral indices from an electron diffraction pattern of a carbon nanotube, is approached from the relationship between the electron scattering intensity distribution and the chiral indices (u, v). We show that electron diffraction patterns can provide an accurate and unambiguous assignment of the chiral indices of carbon nanotubes. The chiral indices (u, v) can be read indiscriminately with a high accuracy from the intensity distribution on the principal layer lines in an electron diffraction pattern.The symmetry properties of electron diffraction from carbon nanotubes and the electron diffraction from deformed carbon nanotubes are also discussed in detail. It is shown that 2mm symmetry is always preserved for single-walled carbon nanotubes, but it can break down for multiwalled carbon nanotubes under some special circumstances.Finally, determination of the handedness of carbon nanotubes using electron diffraction is reviewed and discussed with both theoretical analysis and experimental examples.

Using a nonadiabatic evolution method, we investigate the spin filter effect in organic polymers in the presence of a local magnetic field. Through a spin-dependent magnetic field, polarons (charge carrier) with different spins will feel repulsive or attractive force determined by their spins. Our simulations show that in a single-site magnetic field (affecting electrons at a single site), for example V150 = 0.35 eV, or V150 = 0.45 eV, a spin-up polaron accelerated to saturated velocity by an electric field can pass through the field while the spin-down polaron is trapped. When the local field extends over several sites (Vn~exp[−(n−nc)2/n2w]), similar behaviour is also found. Simultaneously we find that it is more likely to realize the spin filter effect in a comparatively large field since the polaron which feels attractive force is easily trapped by a local magnetic field.

The definition and the criterion of a unified symmetry for a Hamilton system are presented. The sufficient condition under which the Noether symmetry is a unified symmetry for the system is given. A new conserved quantity, as well as the Noether conserved quantity and the Hojman conserved quantity, deduced from the unified symmetry, is obtained. An example is finally given to illustrate the application of the results.

A new method is used to determine the nonclassical potential symmetry generators of Burgers equation. Some classes of new explicit solutions, which cannot be obtained by Lie symmetry group of Burgers equation or its integrated equation, are obtained by using these new nonclassical potential symmetry generators.

The superconductivity and the lattice properties of a sintered MgB2 material have been investigated under high pressure up to 10 GPa. The transition temperature was found to decrease linearly with increasing hydrostatic pressure at a rate of 1.03 K GPa−1, which can be explained with the classical Bardeen–Cooper–Shrieffer theory based on an electron–phonon coupling mechanism. The crystal lattice exhibits an anisotropic compressibility characterized by a larger compressibility along the c-direction than the a/b-directions. The anisotropy is attributed to a weaker inter-plane bonding along the c-axis in comparison with a stronger intra-plane bonding perpendicular to the c-axis. The bulk modulus of the measured material was deduced to be 172 GPa.

It was found by the x-ray diffraction experiment under hydrostatic pressure that the carbon nanotubes are compressed easily with a high volume compressibility of 0.024 GPa−1. The single-walled carbon nanotubes are polygonized when they form bundles of hexagonal close-packed structure and the inter-tubular gap is smaller than the equilibrium spacing of graphite. Under high pressure, further polygonization occurs to accommodate the extra amount of volume reduction. The ratio of the short and the long diagonals in the hexagonalized cross section is found to have changed from 0.991 at zero pressure to 0.982 at 1.5 GPa pressure, when the Bragg reflection from the nanotube lattice diminished. Accompanying polygonization, a discontinuous change in electrical resistivity was observed at 1.5 GPa pressure, suggesting a phase transition had occurred.

Within an extended Su-Schrieffer-Heeger model, we investigate the localized phonons in a pristine polyacene chain, in which there is an interchain-coupled neutral soliton of D2h symmetry. In addition to three pairs of twofold-degenerate edge modes (three infrared active and three Raman active), we found in total nine localized modes, among which four (three B2u and one B3u) modes are infrared active and the others (two Ag and three B1g) modes are Raman active.

Using a nonadiabatic evolution method, we investigate the spin-flip process of polaron in polymers with a magnetic impurity. Our results show that when the spin orientation of this impurity is fixed to be perpendicular to the spin of polaron (? = ?/2), the magnetic impurity causes a spin-flip process. The probability of the spin-flip increases with the increase of exchange integral J up to about 0.35?eV and then decreases with the increase of J. In the case J is fixed while the spin orientation is adjustable, we find the probability of the spin-flip varies with the impurity orientation and reaches a maximum value at ? = ?/2.

Based on the modified Su-Schrieffer-Heeger Hamiltonian and by adding the interchain hopping term, we consider the effect of interchain coupling on quantum lattice fluctuation in transpolyacetylene. It has been found that the interchain coupling does not always weaken quantum lattice fluctuation. After overcoming a barrier of 1 eV or so, the quantum lattice fluctuation can induce a transition of interchain order. The physical meaning of these features is discussed.

By an ab initio calculation based on the local density approximation of density-functional theory, the force constants up to the third nearest-neighbour carbon-hydrogen unit are determined to obtain the phonon spectrum of trans-polyacetylene for the first time. The calculated phonon frequencies at the point coincide well with those of the observed infrared and Raman spectra of trans-polyacetylene. The motion of hydrogen atoms is shown to be important in determining the phonon spectrum of polyacetylene due to the contribution of the bending between the CH and CC bonds.

The effect of electron correlation on the width of the soliton in polymer is studied. Our theory shows that the screening plays a key role in the effect of electron correlation on the width of soliton: In weak screening, the width of soliton is reduced by the electron-electron interaction; whereas, in strong screening, it will be increased. The physical reason is given at the end.

We report the first result of measurements of the lateral distribution of Cerenkov light associated with cosmic ray extensive air showers with size between 105.0 and 106.6 observed in the Liangwang Mountain Observatory, 90 km east of Kunming City in China. The change trend towards heavy nucleus dominance of the primary cosmic ray composition in the `knee' region is deduced with the aid of a Monte Carlo simulation.

Quantum heat transport in a spin-boson system under nonequilibrium steady state (NESS) is investigated by the nonequilibrium Green's function (NEGF) method. Spin-spin correlators are calculated via the Majorana fermion representation of spin operators, which allows us to make use of Wick's theorem through standard diagrammatic techniques. An analytic formula of heat current is obtained, and numerical results are presented in comparison with those obtained by other methods. Two types of transport mechanisms are identified in high- and low-temperature regions, respectively, which shows a transition from incoherent to coherent transport process with the baths' temperatures decreased. Additionally, a saturation of the heat current is confirmed when increasing the coupling strength between the baths and the intermediate system, which is a sign of quantum Zeno effect (QZE) in the transport process.

Conservation laws of some differential equations in fiance are studied in this paper. This method does not involve the use or existence of a variational principle. As an alternative, linearize the given equation and find adjoint equation of the linearized equation, the conservation laws can be constructed directly from the symmetries and adjoint symmetries of the associated linearized equation and its adjoint equation.

Non-equilibrium electronic transport through a polymer chain is investigated by the scattering state operator method. The polymer chain is described by an electron-lattice coupling model and its two ends are connected with metal electrodes of different chemical potentials. The scattering states are shown to be a set of complete eigenstates of electrons in the system at non-equilibrium steady state. With this method, we show that the non-equilibrium Peierls transition (NEPT) does not survive the lattice relaxation and the soliton-antisoliton pair excitations. Furthermore the electronic transport is shown to be accomplished through the soliton-lattice energy band.

The effects of polarization and related structural parameters on the intersubband transitions of AlGaN/GaN multi-quantum wells (MQWs) have been investigated by solving the Schrodinger and the Poisson equations self-consistently. The results show that the intersubband absorption coefficient increases with increasing polarization while the transition wavelength decreases, which is not identical to the case of the interband transitions. Moreover, it suggests that the well width has a greater effect on the intersubband transitions than the barrier thickness, and the intersubband transition wavelength of the structure when doped in the barrier is shorter than that when doped in the well. It is found that the influences of the structural parameters differ for different electron subbands. The mechanisms responsible for these effects have been investigated in detail.

By employing an adaptive time-dependent density matrix renormalization group (t-DMRG) method, we investigate the electron-electron correlation effects on the inelastic-scattering processes of oppositely charged-soliton anti-soliton pairs in conjugated polymers under the influence of an external electric field. The simulations are performed based on the Su-Schrieffer-Heeger (SSH) model modified to include electron-electron interactions and an external electric field. The percent yield of product is numerically calculated by a projection method. Our results show that the on-site Coulomb interaction is of fundamental importance and favors the recombination between the pairs of soliton. Additionally, the effects of external electric field and nearest-neighbor electron-electron interaction on the collision processes are also discussed.

Carbon nanotubes (CNTs) are among the most highly studied nanomaterials due to their unique (and intertwined) mechanical and electrical properties. Recent advances in fabrication have allowed devices to be fabricated that are capable of applying a twisting force to individual CNTs while measuring mechanical and electrical response. Here, we review major results from this emerging field of study, revealing new properties of the material itself and opening possibilities for advances in future devices.

We investigate the quantum phase transitions in the half-filled ionic Hubbard model on a two-dimensional (2D) square lattice using the variational cluster approach (VCA). We present explicit evidence for the tendency toward a novel intermediate phase in this model. This phase is characterized by bond-located magnetization. For weak Coulomb repulsion U, the system is a band insulator, and then undergoes a transition to the intermediate phase at the first-phase boundary U=Uc1. As U is increased beyond the second transition point Uc2, there occurs a Mott insulator accompanied by a long-range antiferromagnetic (AF) order. The bond-located spin density wave competes with the antiferromagnetism while the charge-density modulation exists all the way due to the staggered potential Δ.