[en] Graphical abstract: Relationships between the conductivities of LFPC-2 cathode and the volume percentages of AB (a) and PAn (b). - Highlights: • LiFe_0.94Mg_0.03Cu_0.03PO₄/C is synthesized by adding glucose with two-step method. • Conductive polymer polyaniline is used to replace acetylene black. • The content of conductive additive is optimized by the percolation theory. • LFPC-2 cathode containing polyaniline possesses the excellent performance. - Abstract: Comprehensive methods were utilized to improve the electrochemical performances of LiFe_0.94Mg_0.03Cu_0.03PO₄/C (LFPC) composite cathode. Experimental results show that LFPC-2, prepared by adding glucose in two steps, possesses the effective incorporated of doping ions and well-distributed pyrolysis carbon. It possesses higher conductivity and discharge capacity. The percolation theory analysis shows that the conductivity of LFPC-2 cathode film reaches its maximum value at the mass content of 15 wt.%. The replacement of acetylene black with polyaniline can greatly improve the electrochemical performances of LFPC-2 cathode. Its discharge capacity is 85.3 mAh g⁻¹ and its potential platform is as high as 3.2 V at the current density of 850 mA g⁻¹ when 15 wt.% polyaniline is used. The cycle performance of LFPC-2 is improved when polyaniline is used as conductive additives. And the change of charge transfer resistance of LFPC-2 cathode containing polyaniline is very small after 24 cycles

[en] Radioactive source, used in traditional density logging, has great impact on the environment, while the pulsed neutron source applied in the logging tool is more safety and greener. In our country, the pulsed neutron-gamma density logging technology is still in the stage of development. Optimizing the parameters of neutron-gamma density instrument is essential to improve the measuring accuracy. This paper mainly studied the effects of spacing to typical neutron-gamma density logging tool which included one D-T neutron generator and two gamma scintillation detectors. The optimization of spacing were based on measuring sensitivity and counting statistic. The short spacing from 25 to 35 cm and long spacing from 60 to 65 cm were selected as the optimal position for near and far detector respectively. The result can provide theoretical support for design and manufacture of the instrument. (authors)

[en] Light curves of solar-type stars often show gradual fluctuations due to rotational modulation by magnetic features (starspots and faculae) on stellar surfaces. Two quantitative measures of modulated light curves are employed as the proxies of magnetic activity for solar-type stars observed with Kepler telescope. The first is named autocorrelation index i_A_C, which describes the degree of periodicity of the light curve; the second is the effective fluctuation range of the light curve R_e_f_f, which reflects the depth of rotational modulation. The two measures are complementary and depict different aspects of magnetic activities on solar-type stars. By using the two proxies i_A_C and R_e_f_f, we analyzed activity properties of two carefully selected solar-type stars observed with Kepler (Kepler ID: 9766237 and 10864581), which have distinct rotational periods (14.7 versus 6.0 days). We also applied the two measures to the Sun for a comparative study. The result shows that both the measures can reveal cyclic activity variations (referred to as i_A_C-cycle and R_e_f_f-cycle) on the two Kepler stars and the Sun. For the Kepler star with the faster rotation rate, i_A_C-cycle and R_e_f_f-cycle are in the same phase, while for the Sun (slower rotator), they are in the opposite phase. By comparing the solar light curve with simultaneous photospheric magnetograms, it is identified that the magnetic feature that causes the periodic light curve during solar minima is the faculae of the enhanced network region, which can also be a candidate of magnetic features that dominate the periodic light curves on the two Kepler stars

[en] Ever since the magnetohydrodynamic (MHD) method for extrapolation of the solar coronal magnetic field was first developed to study the dynamic evolution of twisted magnetic flux tubes, it has proven to be efficient in the reconstruction of the solar coronal magnetic field. A recent example is the so-called data-driven simulation method (DDSM), which has been demonstrated to be valid by an application to model analytic solutions such as a force-free equilibrium given by Low and Lou. We use DDSM for the observed magnetograms to reconstruct the magnetic field above an active region. To avoid an unnecessary sensitivity to boundary conditions, we use a classical total variation diminishing Lax-Friedrichs formulation to iteratively compute the full MHD equations. In order to incorporate a magnetogram consistently and stably, the bottom boundary conditions are derived from the characteristic method. In our simulation, we change the tangential fields continually from an initial potential field to the vector magnetogram. In the relaxation, the initial potential field is changed to a nonlinear magnetic field until the MHD equilibrium state is reached. Such a stable equilibrium is expected to be able to represent the solar atmosphere at a specified time. By inputting the magnetograms before and after the X3.4 flare that occurred on 2006 December 13, we find a topological change after comparing the magnetic field before and after the flare. Some discussions are given regarding the change of magnetic configuration and current distribution. Furthermore, we compare the reconstructed field line configuration with the coronal loop observations by XRT onboard Hinode. The comparison shows a relatively good correlation.

[en] High uniformity of un-doped and Ni-doped CuSe nanowires have been fabricated by smelting the bulk and injecting the molten liquid into the anodic aluminum oxide (AAO) template. The Ni dopant concentration and morphology of CuSe nanowires can be well controlled via preparing the bulk materials and the channel size of the AAO template, respectively. The cathodoluminescence peaks of the un-doped, 0.5 at% and 1.0 at% Ni-doped CuSe nanowires showed a redshift of about 26 nm and 42 nm, respectively, from un-doped CuSe nanowires (579 nm). Furthermore, above room temperature ferromagnetism was observed in 1.0 at% Ni-doped CuSe nanowires at 300 K. The facile injection molding method fabricated nanowires with tunable optical and magnetic properties which could be applied to prepare various nanomaterials for spintronic devices in the future. (paper)

[en] We present a careful assessment of forced field extrapolation using the Solar Dynamics Observatory /Helioseismic and Magnetic Imager magnetogram. We use several metrics to check the convergence property. The extrapolated field lines below 3600 km appear to be aligned with most of the H α fibrils observed by the New Vacuum Solar Telescope. In the region where magnetic energy is far larger than potential energy, the field lines computed by forced field extrapolation are still consistent with the patterns of H α fibrils while the nonlinear force-free field results show a large misalignment. The horizontal average of the lorentz force ratio shows that the forced region where the force-free assumption fails can reach heights of 1400–1800 km. The non-force-free state of the chromosphere is also confirmed based on recent radiation magnetohydrodynamics simulations.

[en] The Thomson scattering theory indicates that there exist explicit and implicit ambiguities in polarimetric analyses of coronal mass ejection (CME) observations. We suggest a classification for these ambiguities in CME reconstruction. Three samples, including double explicit, mixed, and double implicit ambiguity, are shown with the polarimetric analyses of STEREO CME observations. These samples demonstrate that this classification is helpful for improving polarimetric reconstruction.

[en] The mass of a coronal mass ejection (CME) is calculated from the measured brightness and assumed geometry of Thomson scattering. The simplest geometry for mass calculations is to assume that all of the electrons are in the plane of the sky (POS). With additional information like source region or multiviewpoint observations, the mass can be calculated more precisely under the assumption that the entire CME is in a plane defined by its trajectory. Polarization measurements provide information on the average angle of the CME electrons along the line of sight of each CCD pixel from the POS, and this can further improve the mass calculations as discussed here. A CME event initiating on 2012 July 23 at 2:20 UT observed by the Solar Terrestrial Relations Observatory is employed to validate our method

[en] Chebyshev segmentation method was used to discretize the time period contained in delay differential equation, then the Newton second-order difference quotient method was used to calculate the cutter motion vector at each time endpoint, and the Floquet theory was used to determine the stability of the milling system after getting the transfer matrix of milling system. Using the above methods, a two degree of freedom milling system stability issues were investigated, and system stability lobe diagrams were got. The results showed that the proposed methods have the following advantages. Firstly, with the same calculation accuracy, the points needed to represent the time period are less by the Chebyshev Segmentation than those of the average segmentation, and the computational efficiency of the Chebyshev Segmentation is higher. Secondly, if the time period is divided into the same parts, the stability lobe diagrams got by Chebyshev segmentation method are more accurate than those of the average segmentation. (paper)

[en] Previous statistical analyses of a large number of SOHO/MDI full disk longitudinal magnetograms provided a result that demonstrated how responses of solar flares to photospheric magnetic properties can be fitted with sigmoid functions. A logistic model reveals that these fitted sigmoid functions might be related to the free energy storage process in solar active regions. Although this suggested model is rather simple, the free energy level of active regions can be estimated and the probability of a solar flare with importance over a threshold can be forecast within a given time window. (research paper)