Stability of Runge–Kutta methods for the alternately advanced and retarded differential equations with piecewise continuous arguments

AbstractThis paper deals with the numerical properties of Runge–Kutta methods for the solution of u′(t)=au(t)+a0u([t+12]). It is shown that the Runge–Kutta method can preserve the convergence order. The necessary and sufficient conditions under which the analytical stability region is contained in the numerical stability region are obtained. It is interesting that the θ-methods with 0⩽θ<12 are asymptotically stable. Some numerical experiments are given

A New Metaheuristic Bat-Inspired Algorithm

Metaheuristic algorithms such as particle swarm optimization, firefly algorithm and harmony search are now becoming powerful methods for solving many tough optimization problems. In this paper, we propose a new metaheuristic method, the Bat Algorithm, based on the echolocation behaviour of bats. We also intend to combine the advantages of existing algorithms into the new bat algorithm. After a detailed formulation and explanation of its implementation, we will then compare the proposed algorithm with other existing algorithms, including genetic algorithms and particle swarm optimization. Simulations show that the proposed algorithm seems much superior to other algorithms, and further studies are also discussed.Comment: 10 pages, 2 figure

Contributions to the cross shock electric field at supercritical perpendicular shocks: Impact of the pickup ions

A particle-in-cell code is used to examine contributions of the pickup ions (PIs) and the solar wind ions (SWs) to the cross shock electric field at the supercritical, perpendicular shocks. The code treats the pickup ions self-consistently as a third component. Herein, two different runs with relative pickup ion density of 25% and 55% are presented in this paper. Present preliminary results show that: (1) in the low percentage (25%) pickup ion case, the shock front is nonstationary. During the evolution of this perpendicular shock, a nonstationary foot resulting from the reflected solar wind ions is formed in front of the old ramp, and its amplitude becomes larger and larger. At last, the nonstationary foot grows up into a new ramp and exceeds the old one. Such a nonstationary process can be formed periodically. hen the new ramp begins to be formed in front of the old ramp, the Hall term mainly contributed by the solar wind ions becomes more and more important. The electric field Ex is dominated by the Hall term when the new ramp exceeds the old one. Furthermore, an extended and stationary foot in pickup ion gyro-scale is located upstream of the nonstationary/self-reforming region within the shock front, and is always dominated by the Lorentz term contributed by the pickup ions; (2) in the high percentage (55%) pickup ion case, the amplitude of the stationary foot is increased as expected. One striking point is that the nonstationary region of the shock front evidenced by the self-reformation disappears. Instead, a stationary extended foot dominated by Lorentz term contributed by the pickup ions, and a tationary ramp dominated by Hall term contributed by the solar wind ions are clearly evidenced. The significance of the cross electric field on ion dynamics is also discussed.Comment: 11 pages, 6 figs and 1 table. This paper will be published in the journal: Astrophysics and Space Scienc

The Vacuum System of HIRFL

AbstractThe vacuum system of Heavy Ion Research Facility in Lanzhou (HIRFL) is a large and complex system. HIRFL consists of two ECR ion sources, a sector focus cyclotron (SFC), a separate sector cyclotron (SSC) and a multi-purpose cooling storage ring system which has a main ring (CSRm) and an experiment ring (CSRe). Several beam lines connect these accelerators together and transfer various heavy ion beams to more than 10 experiment terminals. According to the requirements of the ion acceleration and ion lifetime, the working pressure in each accelerator is different. SFC is nearly 50 years old. After upgrade, the working pressure in SFC is improved from 10-6mbar to 10-8mbar. The pressure in SSC which was built in the 1980s reaches the same level. The cooling storage ring system with a length of 500m came into operation in 2007. The average pressures in CSRm and CSRe are 5×10-12mbar and 8×10-12mbar respectively. Different designs were adopt for vacuum system of a dozen beam lines to meet specific requirement of each experiment terminal. Along with the extensive development of the heavy ion researches and applications, new accelerators of HIRFL are under construction. The vacuum system of the new machines will be designed and constructed followed the overall schedule

Spin polarized tunneling in ferromagnet/unconventional superconductor junctions

We study tunneling in ferromagnet/unconventional superconductor (F/S) junctions. We include the effects of spin polarization, interfacial resistance, and Fermi wavevector mismatch (FWM) between the F and S regions. Andreev reflection (AR) at the F/S interface, governing tunneling at low bias voltage, is strongly modified by these parameters. The conductance exhibits a very wide variety of features as a function of applied voltage.Comment: Revision includes new figures with angular averages and correction of minor error

Dimensional Crossover of Vortex Dynamics Induced by Gd Substitution on Bi2212 Single Crystals

The vortex dynamics of Bi$_2$Sr$_2$Ca$_{1-x}$Gd$_x$Cu$_2$O$_{8+\delta}$ single crystals is investigated by magnetic relaxation and hysteresis measurements. By substituting $Ca$ with $Gd$, it is found that the interlayer Josephson coupling is weakened and the anisotropy is increased, which leads to the change of vortex dynamics from 3D elastic to 2D plastic vortex creep. Moreover, the second magnetization peak, which can be observed in samples near the optimal doping, is absent in the strongly underdoped (with 2D vortex) region.Comment: 16 Pages, 6 Figures, To appear in Physica

Current and Spin-Torque in Double Tunnel Barrier Ferromagnet - Superconductor - Ferromagnet Systems

We calculate the current and the spin-torque in small symmetric double tunnel barrier ferromagnet - superconductor - ferromagnet (F-S-F) systems. Spin-accumulation on the superconductor governs the transport properties when the spin-flip relaxation time is longer than the transport dwell time. In the elastic transport regime, it is demonstrated that the relative change in the current (spin-torque) for F-S-F systems equals the relative change in the current (spin-torque) for F-N-F systems upon changing the relative magnetization direction of the two ferromagnets. This differs from the results in the inelastic transport regime where spin-accumulation suppresses the superconducting gap and dramatically changes the magnetoresistance [S. Takahashi, H. Imamura, and S. Maekawa, Phys. Rev. Lett. 82, 3911 (1999)]. The experimental relevance of the elastic and inelastic transport regimes, respectively, as well as the reasons for the change in the transport properties are discussed.Comment: 7 page

Influence of infiltration temperature on the microstructure and oxidation behavior of SiC-ZrC ceramic coating on C/C composites prepared by reactive melt infiltration

SiC–ZrC ceramic coating on C/C composites was prepared by reactive melt infiltration (RMI) using a powder mixture composed of Zr, Si and C as the infiltrator. The phase composition and microstructure of the ceramic coating were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The oxidation resistance of the as-prepared composites was tested at 1550 °C in static air. The results indicate that the infiltration temperature has remarkable effects on the phase composition and microstructure of the ceramic coating, as well as on the oxidation resistance of the composites. The SiC–ZrC coated C/C composites prepared at 2000 °C exhibit an excellent oxidation resistance. They gain weight about 5.9 wt% after oxidation at 1550 °C in static air for 5 h, whereas the SiC–ZrC coated C/C composites prepared at 1800 °C lose weight about 3.2 wt%. As a comparison, SiC coated C/C composites prepared at 2000 °C by RMI show an inferior oxidation resistance. After 5 h oxidation, SiC coated C/C composites are severely damaged and their weight loss reaches up to 44.3 wt%. The outstanding oxidation resistance of the SiC–ZrC coated C/C composites prepared at 2000 °C can be attributed to the rapid formation of a continuous glass-like layer composed of ZrO2, ZrSiO4 and SiO2, which covers the surface of the composites and retards the oxygen diffusion and the attack on the underlying C/C substrate. For SiC coated C/C composites, the large SiC particles formed on the surface of the composites are difficult to oxidize rapidly and so a continuous and dense SiO2 layer cannot be formed in time to significantly hinder fast oxygen diffusion leading to the consequent severe oxidation of the C/C substrate

Finding needles in haystacks: Linking scientific names, reference specimens and molecular data for Fungi

DNA phylogenetic comparisons have shown that morphology-based species recognition often underestimates fungal diversity. Therefore, the need for accurate DNA sequence data, tied to both correct taxonomic names and clearly annotated specimen data, has never been greater. Furthermore, the growing number of molecular ecology and microbiome projects using high-throughput sequencing require fast and effective methods for en masse species assignments. In this article, we focus on selecting and re-annotating a set of marker reference sequences that represent each currently accepted order of Fungi. The particular focus is on sequences from the internal transcribed spacer region in the nuclear ribosomal cistron, derived from type specimens and/or ex-type cultures. Reannotated and verified sequences were deposited in a curated public database at the National Center for Biotechnology Information (NCBI), namely the RefSeq Targeted Loci (RTL) database, and will be visible during routine sequence similarity searches with NR_prefixed accession numbers. A set of standards and protocols is proposed to improve the data quality of new sequences, and we suggest how type and other reference sequences can be used to improve identification of Fungi.B.R. and C.L.S. acknowledge support from the Intramural Research Program of the National Institutes of Health, National Library of MedicinePeer Reviewe