The accretion rate independence of horizontal branch oscillation in XTE J1701-462

We study the temporal and energy spectral properties of the unique neutron star low-mass X-ray binary XTE J1701-462. After assuming the HB/NB vertex as a reference position of accretion rate, the horizontal branch oscillation (HBO) of the HB/NB vertex is roughly 50 Hz. It indicates that the HBO is independent with the accretion rate or the source intensity. The spectral analysis shows $R_{\rm{in}}\propto\dot{M}_{\rm{Disk}}^{2.9\pm0.09}$ in the HB/NB vertex and $R_{\rm{in}}\propto\dot{M}_{\rm{Disk}}^{1.7\pm0.06}$ in the NB/FB vertex, which implies that different accretion rate may be produced in the HB/NB vertex and the NB/FB vertex. The Comptonization component could be fitted by constrained broken power law (CBPL) or nthComp. Different with GX 17+2, the frequencies of HBO positively correlate with the inner disk radius, which contradict with the prediction of Lense-Thirring precession model. XTE J1701-462, both in the Cyg-like phase and in the Sco-like phase, follows a positive correlation between the break frequency of broad band noise and the characteristic frequency of HBO, which is called the W-K relation. An anticorrelation between the frequency of HBO and photon energy is observed. Moreover, the rms of HBO increases with photon energy till ~10 keV. We discuss the possible origin of HBO from corona in XTE J1701-462.Comment: 45 pages, 18 figures, accepted by Ap

A nonautonomous predator–prey system with stage structure and double time delays

AbstractIn the present paper we study a nonautonomous predator–prey model with stage structure and double time delays due to maturation time for both prey and predator. We assume that the immature and mature individuals of each species are divided by a fixed age, and the mature predator only attacks the immature prey. Based on some comparison arguments we discuss the permanence of the species. By virtue of the continuation theorem of coincidence degree theory, we prove the existence of positive periodic solution. By means of constructing an appropriate Lyapunov functional, we obtain sufficient conditions for the uniqueness and the global stability of positive periodic solution. Two examples are given to illustrate the feasibility of our main results

Fishtail effect and the vortex phase diagram of single crystal Ba0.6K0.4Fe2As2

By measuring the magnetization hysteresis loops of superconducting Ba0.6K0.4Fe2As2 single crystals, we obtained the high upper critical field and large current carrying ability, which point to optimistic applications. The fishtail (or second peak) effect is also found in the material, and the position of the vortex pinning force shows a maximum at 1/3 of the reduced field, being consistent with the picture of vortex pinning by small size normal cores in the sample. Together with the resistive measurements, for the first time the vortex phase diagram is obtained for superconductor Ba0.6K0.4Fe2As2.Comment: 4 pages, 5 figure

Vortex creep and critical current densities in superconducting (Ba,K)Fe2_{2}As2_{2} single crystals

The surprisingly rapid relaxation of the sustainable current density in the critical state of single crystalline Ba$_{1-x}$K$_{x}$Fe$_{2}$As$_{2}$ is investigated for magnetic fields oriented parallel to the c-axis and to the $ab$--plane respectively. Due to the inadequacy of standard analysis procedures developed for flux creep in the high temperature superconducting cuprates, we develop a simple, straightforward data treatment technique that reveals the creep mechanism and the creep exponent $\mu$. At low magnetic fields, below the second magnetization peak, $\mu$ varies only slightly as function of temperature and magnetic flux density $B$. From the data, we determine the temperature- and field dependence of the effective activation barrier for creep. At low temperatures, the measured current density approaches the zero--temperature critical current density (in the absence of creep) to within a factor 2, thus lending credence to earlier conclusions drawn with respect to the pinning mechanism. The comparable values of the experimental screening current density and the zero-temperature critical current density reveals the limited usefulness of the widely used "interpolation formula".Comment: Physical Review B (2012) Accepte

Superconductivity at 36 K in Gadolinium-arsenide Oxides GdO1−x_{1-x}Fx_{x}FeAs

In this paper we report the fabrication and superconducting properties of GdO$_{1-x}$F$_{x}$FeAs. It is found that when x is equal to 0.17, GdO$_{0.83}$F$_{0.17}$FeAs is a superconductor with the onset transition temperature T$_{c}^{on}\approx$ 36.6K. Resistivity anomaly near 130K was observed for all samples up to x = 0.17, such a phenomenon is similar to that of LaO$_{1-x}$F$_{x}$FeAs. Hall coefficient indicates that GdO$_{0.83}$F$_{0.17}$FeAs is conducted by electron-like charge carriers.Comment: 3 pages, 4 figure

Evaluation of Spatial and Temporal Performances of ERA-Interim Precipitation and Temperature in Mainland China

ERA-Interim has been widely considered as a valid proxy for observations at global and regional scales. However, the verifications of ERA-Interim precipitation and temperature in mainland China have been rarely conducted, especially in the spatial and long-term performances. Therefore, in this study, we employed the interpolated ground station (STA) data to evaluate the spatial and temporal patterns and trends of ERA-Interim precipitation and temperature during 1980-2012. The results showed that relatively weaker performances were observed in ERA-Interim precipitation, with the skill score (S index) ranging from 0.41 to 0.50. Interannual ERA-Interim precipitation presented comparable trends with STA precipitation at the annual and seasonal scales. Spatial patterns of empirical orthogonal function (EOF) modes and corresponding principal components were evidently different between annual ERA-Interim and STA precipitation. For temperature, annual and seasonal patterns of ERA-Interim data were in good consistency with those of STA over China with the S index ranging from 0.59 to 0.70. Yet interannual STA temperature recorded stronger warming trends (from 0.37K decade(-1) of wintertime to 0.53 Kdecade(-1) of springtime) at the annual and seasonal scales compared to corresponding periods for ERA-Interim temperature (from 0.03Kdecade 21 of wintertime to 0.25Kdecade(-1) of summertime). Overall, ERA-Interim precipitation and temperature had good agreement with STA data in east China with lower elevation (< 1000m above sea level), but good agreements were not observed in west China with higher elevation. The findings suggest that caution should be paid when using ERA-Interim precipitation and temperature in areas with complex orography

Fully Gapped Superconducting State Based on a High Normal State Quasiparticle Density of States in Ba0.6_{0.6}K0.4_{0.4}Fe2_2As2_2 Single Crystals

We report the specific heat (SH) measurements on single crystals of hole doped $FeAs$-based superconductor $Ba_{0.6}K_{0.4}Fe_2As_2$. It is found that the electronic SH coefficient $\gamma_e(T)$ is not temperature dependent and increases almost linearly with the magnetic field in low temperature region. These point to a fully gapped superconducting state. Surprisingly the sharp SH anomaly $\Delta C/T|_{T_c}$ reaches a value of 98 $mJ/mol K^2$ suggesting a very high normal state quasiparticle density of states ($\gamma_n \approx 63 mJ/mol K^2$). A detailed analysis reveals that the $\gamma_e(T)$ cannot be fitted with a single gap of s-wave symmetry due to the presence of a hump in the middle temperature region. However, our data indicate that the dominant part of the superconducting condensate is induced by an s-wave gap with the magnitude of about 6 meV.Comment: 5 pages, 5 figure