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We propose a method to retrieve the angle-dependent strong-field ionization of highest occupied molecular orbital (HOMO) from high-order harmonic generation (HHG) of aligned molecules. This method is based on the single-molecule quantitative rescattering model with known alignment distribution and photo-recombination cross sections of fixed-in-space molecules. With the macroscopic HHG of aligned N2 molecules, we show that angle-dependent ionization of HOMO can be successfully retrieved at both low and high degrees of alignment. We then show that the error in the retrieved angular dependence of ionization becomes larger if the uncertainty in the alignment distribution is introduced in the retrieval procedure. We also examine that the retrieved ionization of HOMO is much deviated from the accurate one if the intensity of probe laser becomes higher such that inner HOMO-1 can contribute to HHG.

We theoretically investigate the characteristics of terahertz (THz) radiation from monolayer graphene exposed to normal incident few-cycle laser pulses, by numerically solving the extended semiconductor Bloch equations. Our simulations show that the THz spectra in low frequency regions are highly dependent on the carrier envelope phase (CEP) of driving laser pulses. Using an optimal CEP of few-cycle laser pulses, we can obtain broadband strong THz waves, due to the symmetry breaking of the laser-graphene system. Our results also show that the strength of the THz spectra depend on both the intensity and central wavelength of the laser pulses. The intensity dependence of the THz wave can be described by the excitation rate of graphene, while wavelength dependence can be traced back to the band velocity and the population of graphene. We find that a near single-cycle THz pulse can be obtained from graphene driven by a mid-infrared laser pulse.

We study the feasibility and safety of human lung hyperpolarized (HP) 129 Xe magnetic resonance imaging (MRI). There is no significant change in physiological parameters before and after the examinations of all subjects. Compared with computed tomography, HP 129 Xe MRI is sensitive to earlier and smaller ventilation defects. The distribution of the HP 129 Xe MRI signal reflects the pulmonary compliance with the gravity gradient. This is the first application of HP 129 Xe MRI ventilation imaging in China, and this technology is expected to provide more useful information for clinical practice.

In this paper, a modified Chaplygin gas model of unifying dark energy and dark matter with exotic equation of state $p=B\rho-\frac{A}{\rho^{\alpha}}$ which can also explain the recent accelerated expansion of the universe is investigated by the means of constraining the location of the peak of the CMBR spectrum. We find that the result of CMBR measurements does not exclude the nonzero value of parameter $B$, but allows it in the range $-0.35\lesssim B\lesssim0.025$.

We propose a quintessence model with a cosine-type potential, in which the scalar field Φa possesses an O(N) internal symmetry. The most prominent feature of this model is that it will not reduce to a cosmological constant even when |Φa| is spatially uniform and time-independent. Since different values of the potential parameter will lead to different cosmic microwave background anisotropies, which may be detectable in future satellite experiments, one can decide by observations whether the cosine-type quintessence consists of one scalar field or many fields with a symmetry constraint.

We consider a twisted massless multiplet on a two-torus, one side with a normal boundary and the other with a twisted boundary. The Casimir energy is calculated and regularized by means of the Epstein-Hurwitz-type zeta-function introduced by Elizalde. The resulting dimensions of spacetime for the twisted case may be integers. The results are compared with those of the untwisted case. Since twisted Casimir energy is lower than untwisted energy, the untwisted case may change into the twisted state in the spacetime.

We study the quasinormal modes (QNMs) for stringy black holes. By using numerical calculation, the relations between the QNMs and the parameters of black holes are minutely shown. For (1+1)-dimensional stringy black hole, the real part of the quasinormal frequency increases and the imaginary part of the quasinormal frequency decreases as the mass of the black hole increases. Furthermore, the dependence of the QNMs on the charge of the black hole and the flatness parameter is also illustrated. For (1+3)-dimensional stringy black hole, increasing either the event horizon or the multipole index, the real part of the quasinormal frequency decreases. The imaginary part of the quasinormal frequency increases no matter whether the event horizon is increased or the multipole index is decreased., Comment: 4 pages, 5 figures

The elliptic loop equation of cosmic string is studied in the Minkowski space and during the radiation-dominated era in the Robertson-Walker universe. A remarkable fact about this equation is that a loop may never contract to one with a Schwarzschild radius, if it is sufficiently non-circular.

The mutual neutralization cross sections of Na+/O- ions at low energy have been calculated by using the multichannel Landau-Zener theory. An asymptotic method is used for estimating the coupling matrix elements between the ionic and covalent states at the crossing points of diabatic potential curves. The results of calculation are compared with available experimental data.

We propose an analytical inflation model driven by a scalar field with Born–Infeld-type Lagrangian and compute its power spectrum. The constraints on the parameters of the potential by the recent Wilkinson microwave anisotropy probe data are derived.

We present a new exactly solvable inflation model in which inflation can stop automatically, and in the approximately de Sitter limit, we give its power spectrum which can be tested in the future observations of cosmic microwave background anisotropy.

We consider an electromagnetic perturbation in the external spacetime of a black hole with a deficit angle, and describe the perturbation equation. Approximate analytic formulae for the quasi-normal frequencies have been provided, which may play a significant role in the continuing search for gravitational radiation and black holes. These frequencies can be distinguished from the ordinary quasi-normal frequencies of the Schwarzschild black hole.

Scalar particles might be in the universe as diffuse gaseous clouds or compact objects and might be even present in D-stars. The astrophysical consequences are discussed in detail. Especially, D-stars may be considered as an elegant candidate. The Einstein ring should be observable with MAXIM if D-stars exist. PACS: 04. 20. Jb, 04. 80. -y, 95. 30. Sf, 98. 80. Cq

A modified Wentzel-Kramers-Brillouin approach is used to determine the complex normal-mode frequencies of external perturbations in generalized Schwarzschild geometry. In the ??=?1 case (Schwarzschild geometry), the agreement with other methods is excellent for the low-lying modes. On the contrary, the ? ? 1 case of this geometry is unstable against external perturbations.

By the Hamilton-Jacobi formalism, the features of orbits of a test particle moving in generalized Schwarzschild geometries with the parameter 0 < λ ≤ 1 are studied, where the intensity of λ corresponds to the contribution of massless scalar field. In special case λ = 1, it is reduced to the Schwarzschild metric. It is found that λ = 1/2 is a critical point, when 1/2 ≤ λ < 1 the qualitative features are similar to Schwarzschild geometry whereas the case of 0 < λ < 1/2 is different from the case of λ = 1.

Superconductivity (SC) is one of the most intriguing physical phenomena in nature. Nucleation of SC has long been considered highly unfavorable if not impossible near ferromagnetism, in low dimensionality and, above all, out of non-superconductor. Here we report observation of SC with TC near 4K in Ni/Bi bilayers that defies all known paradigms of superconductivity, where neither ferromagnetic Ni film nor rhombohedra Bi film is superconducting in isolation. This highly unusual SC is independent of the growth order (Ni/Bi or Bi/Ni), but highly sensitive to the constituent layer thicknesses. Most importantly, the SC, distinctively non-s pairing, is triggered from, but does not occur at, the Bi/Ni interface. Using point contact Andreev reflection, we show evidences that the unique SC, naturally compatible with magnetism, is triplet p-wave pairing.

We theoretically investigate the high-order harmonics and attosecond pulses generated in a single mid-infrared and synthesized two- and three-color fields. We demonstrate that one can obtain a sub-cycle field by combining two or more long pulses at incommensurate frequencies, if the phases and amplitudes of each field are properly optimized. Compared with the one-color field, the harmonic yields in synthesized fields can be enhanced more than two orders with the same total laser power. The technique of waveform synthesizing shows the possibility of generating intense single attosecond pulses by using longer driving laser pulses without the need of gating techniques with experiment.

The interference of high-order harmonics generated by two successive gas jets within a single laser pulse is discussed by a modeling with the inclusion of macroscopic propagation of the fundamental and harmonic fields in an ionizing medium. Based on the interference, we show that one can extract the laser Rayleigh range from the interference of harmonics and the accuracy of retrieve is independent of carrier-envelope phase while dependent on the pulse duration. Moreover, we demonstrate that it is possible to optimize the single or range of harmonics with a high ratio relative to the adjacent orders by changing the separation of two gas jets, which is unavailable by using a single gas jet and linear polarized laser pulse.

We deal with the preparation of NiMgZnFeIII-SO4 layered double hydroxides (LDHs) with the layered precursor method and introduce excessive ZnO into the NiMgZnFeIII-SO4 LDHs to produce NixMgyZn1−x−yFe2O4 ferrites that contain massive ZnO. Then the NixMgyZn1−x−yFe2O4 ferrites are treated with NaOH solution to remove ZnO to produce the porous NixMgyZn1−x−yFe2O4 magnetic material: when y = 0, porous NiZnFe2O4 ferrite magnetic materials are obtained; when y ≠ 0, porous NiMgZnFe2O4 ferrite magnetic materials are obtained. From analyses of these two ferrites, their pore-forming mechanism and comparison of their properties before and after they undergo the alkali treatment, we find that after being treated by the NaOH solution, NiZnFe2O4/NiMgZnFe2O4 have better uniform-structure pores, which will greatly expand their pore volume, widen their application scope and improve their magnetic properties.

We study the phase coherence property of Bose-Einstein condensates confined in a one-dimensional optical lattice formed by a standing-wave laser field. The lattice depth is determined using a method of Kapitza-Dirac scattering between a condensate and a short pulse lattice potential. Condensates are then adiabatically loaded into the optical lattice. The phase coherence property of the confined condensates is reflected by the interference patterns of the expanded atomic cloud released from the optical lattice. For weak lattice, nearly all of the atoms stay in a superfluid state. However, as the lattice depth is increased, the phase coherence of the whole condensate sample is gradually lost, which confirms that the sub-condensates in each lattice well have evolved into number-squeezed states.

We experimentally investigate the collective excitation of (87)Rb Bose-Einstein condensates confined in a cigar-shaped magnetic trap (QUIC trap). Using a method of magnetic perturbation, the center-of-mass oscillation of the condensate is excited, so that the radial trapping frequency of the QUIC trap can be precisely determined. A high-order excitation, characterized by a fast shape oscillation, also occurs simultaneously, with a noticeable damping in the oscillation amplitude compared with the oscillation of the center of mass. The measured oscillation frequencies, associated with these two low-energy excitation modes, agree well with theoretical predictions based on the Gross-Pitaevskii equation.

The motion of test particles around D-stars is investigated by Hamilton-Jacobi method. There may exist bound orbits under certain conditions. The trajector with periastrons at large r are Keplerian in form, except for the periastron shift. The trajectory with periastrons at small r, differ markedly from Keplerian orbits. The radius of the most tightly bound is found.