Select
Rectification and phase locking of graphite
Zhen-Bin Zhang, Ru-Juan Jia, Jasmina Tekić, Yang Yang, Cang-Long Wang, Jia-Wei Li, Xiao-Yun Wang, Wen-Shan Duan, Lei Yang
Front. Phys. . 2015, 10 (4 ): 100506-.
https://doi.org/10.1007/s11467-015-0473-1
Rectification phenomena and the phase locking in a two-dimensional overdamped Frenkel–Kontorova model with a graphite periodic substrate were studied. The presence of dc and ac forces in the longitudinal direction causes the appearance of dynamicalmode locking and the steps in the response function of the system. On the other hand, the presence of an ac force in the transverse direction causes the appearance of rectification, even though there is no net dc force in the transverse direction. It is found that whereas the longitudinal velocity increases in a series of steps, rectification in the transverse direction can occur only between two neighbor steps. The amplitude and phase of the external ac driving force affect the depinning force, rectification of the system and particles trajectories.
References |
Related Articles |
Metrics
Select
Toward precision mass measurements of neutron-rich nuclei relevant to r -process nucleosynthesis
B. H. Sun, Yu. A. Litvinov, I. Tanihata, Y. H. Zhang
Front. Phys. . 2015, 10 (4 ): 102102-.
https://doi.org/10.1007/s11467-015-0503-z
The open question of where, when, and how the heavy elements beyond iron enrich our Universe has triggered a new era in nuclear physics studies. Of all the relevant nuclear physics inputs, the mass of very neutron-rich nuclides is a key quantity for revealing the origin of heavy elements beyond iron. Although the precise determination of this property is a great challenge, enormous progress has been made in recent decades, and it has contributed significantly to both nuclear structure and astrophysical nucleosynthesis studies. In this review, we first survey our present knowledge of the nuclear mass surface, emphasizing the importance of nuclear mass precision in r -process calculations. We then discuss recent progress in various methods of nuclear mass measurement with a few selected examples. For each method, we focus on recent breakthroughs and discuss possible ways of improving the weighing of r -process nuclides.
References |
Related Articles |
Metrics
Select
A nonperturbative quantum electrodynamic approach to the theory of laser induced high harmonic generation
Chao Yu, Jingtao Zhang, Zhi-Wei Sun, Zhenrong Sun, Dong-Sheng Guo
Front. Phys. . 2015, 10 (4 ): 103202-.
https://doi.org/10.1007/s11467-014-0429-x
Using nonperturbative quantum electrodynamics, we develop a scattering theory for high harmonic generation (HHG). A transition rate formula for HHG is obtained. Applying this formula, we calculate the spectra of high harmonics generated from different noble gases shined by strong laser light. We study the cutoff property of the spectra. The data show that the cutoff orders of high harmonics are greater than that predicted by the “3.17” cutoff law. As a numerical experiment, the data obtained from our repeated calculations support the newly derived theoretical expression of the cutoff law. The cutoff energy of high harmonics described by the new cutoff law, in terms of the ponderomotive energy U p and the ionization potential energy I p , is 3.34U p + 1.83I p . The higher cutoff orders predicted by this theory are due to the absorption of the extra photons, which participate only the photon-mode up-conversion and do nothing in the photoionization process.
References |
Related Articles |
Metrics
Select
Discrete vortices on anisotropic lattices
Gui-Hua Chen, Hong-Cheng Wang, Zi-Fa Chen
Front. Phys. . 2015, 10 (4 ): 104206-.
https://doi.org/10.1007/s11467-015-0494-9
We consider the effects of anisotropy on two types of localized states with topological charges equal to 1 in two-dimensional nonlinear lattices, using the discrete nonlinear Schr?dinger equation as a paradigm model. We find that on-site-centered vortices with different propagation constants are not globally stable, and that upper and lower boundaries of the propagation constant exist. The region between these two boundaries is the domain outside of which the on-site-centered vortices are unstable. This region decreases in size as the anisotropy parameter is gradually increased. We also consider off-site-centered vortices on anisotropic lattices, which are unstable on this lattice type and either transform into stable quadrupoles or collapse. We find that the transformation of off-sitecentered vortices into quadrupoles, which occurs on anisotropic lattices, cannot occur on isotropic lattices. In the quadrupole case, a propagation-constant region also exists, outside of which the localized states cannot stably exist. The influence of anisotropy on this region is almost identical to its effects on the on-site-centered vortex case.
References |
Related Articles |
Metrics
Select
First-principles investigation of structural, mechanical, electronic, and bonding properties of NaZnSb
Jian-Bing Gu, Chen-Ju Wang, Lin Zhang, Yan Cheng, Xiang-Dong Yang
Front. Phys. . 2015, 10 (4 ): 107101-.
https://doi.org/10.1007/s11467-015-0496-7
The structural, mechanical, electronic, and bonding properties and phase transition of NaZnSb are explored using the generalized gradient approximation based on ab initio plane-wave pseudopotential density functional theory. With the help of the quasi-harmonic Debye model, we probe the Grüneisen parameter, thermal expansivity, heat capacity, Debye temperature, and entropy of NaZnSb in the tetragonal phase. The results indicate that the lattice constants and the bulk modulus and its first pressure derivative agree well with the available theoretical and experimental data. NaZnSb in its ground state structure exhibits a distinct energy gap of about 0.41 eV, which increases with increasing pressure. Our conclusions are consistent with the theoretical predictions obtained by the ABINIT package, but are different from those obtained through the tight-binding linear muffin-tin orbital method. As a result, further experimental and theoretical researches need to be carried out. For the purpose of providing a comparative and complementary study for future research, we first investigate the thermodynamic properties of NaZnSb.
References |
Related Articles |
Metrics
Select
Superconductivity and superfluidity as universal emergent phenomena
Mike Guidry, Yang Sun
Front. Phys. . 2015, 10 (4 ): 107404-.
https://doi.org/10.1007/s11467-015-0502-0
Superconductivity (SC) or superfluidity (SF) is observed across a remarkably broad range of fermionic systems: in BCS, cuprate, iron-based, organic, and heavy-fermion superconductors, and in superfluid helium-3 in condensed matter; in a variety of SC/SF phenomena in low-energy nuclear physics; in ultracold, trapped atomic gases; and in various exotic possibilities in neutron stars. The range of physical conditions and differences in microscopic physics defy all attempts to unify this behavior in any conventional picture. Here we propose a unification through the shared symmetry properties of the emergent condensed states, with microscopic differences absorbed into parameters. This, in turn, forces a rethinking of specific occurrences of SC/SF such as high-T c SC in cuprates, which becomes far less mysterious when seen as part of a continuum of behavior shared by a variety of other systems.
References |
Related Articles |
Metrics
Select
Effect of thermal annealing on sub-band-gap absorptance of microstructured silicon in air
Cao Li-Ping(曹丽萍), Chen Zhan-Dong(陈战东), Zhang Chun-Ling(张春玲), Yao Jiang-Hong(姚江宏)
Front. Phys. . 2015, 10 (4 ): 107801-.
https://doi.org/10.1007/s11467-015-0491-z
The optical absorption properties of femtosecond-laser-made “black silicon” as a function of the annealing conditions were investigated. We found that the annealing process changes the surface morphology and absorption spectroscopy of the “black silicon” samples, and obtained a maximum sub-band-gap absorptance value of approximately 30% by annealing at 1000 °C for 30 min. The thermal relaxation and atomic structural transformation mechanisms are used to describe the lattice recovery and the increase and decrease of the substitutional dopant atom concentration in the microstructured surface during the annealing. Our results confirm that: i) owing to the thermal relaxation, the lattice defects decrease with the increase of the annealing temperature; ii) the quasi-substitutional and interstitial configurations of the doped atoms transform into substitutional arrangements when the annealing temperature increases; iii) the quasi-substitutional and interstitial configurations with higher energies of the doped atoms transform into interstitial configurations with the lowest energy after high-temperature annealing for a long period of time, causing the deactivation or reactivation of the sub-band-gap absorptance by diffusion. The results demonstrate that the annealing can improve the properties of “black silicon”, including defects repairing, carrier lifetime lengthening, and retention of a high absorptive performance.
References |
Related Articles |
Metrics
14 articles