R-Mode Oscillations in Rotating Magnetic Neutron Stars

We show that r-mode oscillations distort the magnetic fields of neutron stars and that their occurrence is likely to be limited by this interaction. If the field is gtrsim 10^{16} (Omega/Omega_B) G, where Omega and Omega_B are the angular velocities of the star and at which mass shedding occurs, r-mode oscillations cannot occur. Much weaker fields will prevent gravitational radiation from exciting r-mode oscillations or damp them on a relatively short timescale by extracting energy from the modes faster than gravitational wave emission can pump energy into them. For example, a 10^{10} G poloidal magnetic field that threads the star's superconducting core is likely to prevent the ell=2 mode from being excited unless Omega exceeds 0.35 Omega_B. If Omega is larger than 0.35 Omega_B initially, the ell=2 mode may be excited but is likely to decay rapidly once Omega falls below 0.35 Omega_B, which happens in lesssim 15^d if the saturation amplitude is gtrsim 0.1. The r-mode oscillations may play an important role in determining the structure of neutron star magnetic fields.Comment: 4 pages, 1 postscript figure, uses emulateapj; submitted to ApJ Letters 1999 Nov 8; accepted 2000 Jan 25; this version is essentially identical to the original version except that Figure 2 was deleted in order to fit within the ApJ Letters page limi

Crystalline-Electric-Field Effect on the Resistivity of Ce-based Heavy Fermion Systems

The behavior of the resistivity of Ce-based heavy fermion systems is studied using a 1/$N$-expansion method a la Nagoya, where $N$ is the spin-orbital degeneracy of f-electrons. The 1/$N$-expansion is performed in terms of the auxiliary particles, and a strict requirement of the local constraints is fulfilled for each order of 1/N. The physical quantities can be calculated over the entire temperature range by solving the coupled Dyson equations for the Green functions self-consistently at each temperature. This 1/N-expansion method is known to provide asymptotically exact results for the behavior of physical quantities in both low- and high-energy regions when it is applied to a single orbital periodic Anderson model (PAM). On the basis of a generalized PAM including crystalline-electric-field splitting with a single conduction band, the pressure dependence of the resistivity is calculated by parameterizing the effect of pressure as the variation of the hybridization parameter between the conduction electrons and f-electrons. The main result of the present study is that the double-peak structure of the $T$-dependence of the resistivity is shown to merge into a single-peak structure with increasing pressure.Comment: 37 pages, 22 figure

Medium Effects in Cooling of Neutron Stars and 3P23P_2 Neutron Gap

We study the dependence of the cooling of isolated neutron stars on the magnitude of the $3P_2$ neutron gap. It is demonstrated that our ``nuclear medium cooling'' scenario is in favor of a suppressed value of the $3P_2$ neutron gap.Comment: 18 p., 12 figs., extended version of astro-ph/0501678, accepted in A&

Combined Analysis of X-Ray Spectra of NGC 3227

The 1.5 Seyfert galaxy NGC 3227 has been observed by several X-ray missions. We carried out combined analysis of the data obtained by more recent major observations of this source - two observations performed by XMM-Newton in 2000 and 2006 and six observations performed by Suzaku in 2008. A unified model was constructed which is consistent with all eight of the observations by the two satillites with large intensity and spectral changes. The model consists of a hard power law with the spectral index of Gamma_Hard=1.4-1.7 which is interpreted as the Comptonized emission from the corona above an accretion disk. In the high flux states an additional soft excess component dominates, which is consistent with a model with either a steeper power law with Gamma_Soft=3.3-3.85 or the warm Comptonization component. These emissions from the central engine are absorbed by a neutral partial covering material and warm absorbers. A reflection component and several emission lines are also present. We examined the relationship between the intrinsic luminosity and the absorbers' physical parameters such as the column density, which suggests that the source expanded significantly during the bright states where the soft excess is greatly enhanced.Comment: 24 pages, 5 tables, and 17 figure

Thermodynamics of a two-dimensional Yukawa fluid

Thermodynamic quantities of a two-dimensional Yukawa system, a model for various systems including single-layered dust particles observed in dusty plasmas, are obtained and expressed by simple interpolation formulas. In the domain of weak coupling, the analytical method based on the cluster expansion is applied and, in the domain of intermediate and strong coupling, numerical simulations are performed. Due to reduced dimensionality, the treatment based on the mean field fails at the short range and exact behavior of the binary correlation is to be taken into account even in the case of weak coupling.</p

Superfluid Friction and Late-time Thermal Evolution of Neutron Stars

The recent temperature measurements of the two older isolated neutron stars PSR 1929+10 and PSR 0950+08 (ages of $3\times 10^6$ and $2\times 10^7$ yr, respectively) indicate that these objects are heated. A promising candidate heat source is friction between the neutron star crust and the superfluid it is thought to contain. We study the effects of superfluid friction on the long-term thermal and rotational evolution of a neutron star. Differential rotation velocities between the superfluid and the crust (averaged over the inner crust moment of inertia) of $\bar\omega\sim 0.6$ rad s$^{-1}$ for PSR 1929+10 and $\sim 0.02$ rad s$^{-1}$ for PSR 0950+08 would account for their observed temperatures. These differential velocities could be sustained by pinning of superfluid vortices to the inner crust lattice with strengths of $\sim$ 1 MeV per nucleus. Pinned vortices can creep outward through thermal fluctuations or quantum tunneling. For thermally-activated creep, the coupling between the superfluid and crust is highly sensitive to temperature. If pinning maintains large differential rotation ($\sim 10$ rad s$^{-1}$), a feedback instability could occur in stars younger than $\sim 10^5$ yr causing oscillations of the temperature and spin-down rate over a period of $\sim 0.3 t_{\rm age}$. For stars older than $\sim 10^6$ yr, however, vortex creep occurs through quantum tunneling, and the creep velocity is too insensitive to temperature for a thermal-rotational instability to occur. These older stars could be heated through a steady process of superfluid friction.Comment: 26 pages, 1 figure, submitted to Ap

Nonlinear magnetic responses at the phase boundaries around helimagnetic and skyrmion lattice phases in MnSi: Evaluation of robustness of noncollinear spin texture

The phase diagram of a cubic chiral magnet MnSi with multiple Dzyaloshinskii-Moriya (DM) vectors as a function of temperature T and dc magnetic field Hdc was investigated using intensity mapping of the odd-harmonic responses of ac magnetization (M1ω andM3ω), and the responses at phase boundaries were evaluated according to a prescription [J. Phys. Soc. Jpn. 84, 104707 (2015)]. By evaluating M3ω/M1ω appearing at phase boundaries, the robustness of noncollinear spin texture in both the helimagnetic (HM) and the skyrmion lattice (SkL) phases of MnSi was discussed. The robustness of vortices-type solitonic texture SkL in MnSi is smaller than those of both the single DM HM and chiral soliton lattice phases of a monoaxial chiral magnet Cr1/3NbS2, and furthermore the robustness of the multiple DM HM phase in MnSi is smaller than that of its SkL. Through magnetic diagnostics over the wide T -Hdc range, we found a new paramagnetic (PM) region with ac magnetic hysteresis, where spin fluctuations have been observed via electrical magnetochiral effect. The anomalies observed in the previous ultrasonic attenuation measurement correspond to the peak positions of out-of-phase M1ω. The appearance of a new PM region occurs at a characteristic magnetic field, above which indeed the SkL phase appears. It has us suppose that the new PM region could be a phase with spin fluctuation like the skyrmion gas phase

Genetic Diversity in Zoysiagrass Ecotypes Based on Morphological Characteristics and SSR Markers

Zoysiagrass consists of a number of interfertile species, some of which are important grasses for turfgrass and grazing pasture in Japan. Recently, we developed simple sequence repeats (SSRs) markers from Zoysia japonica “Asagake” genomic DNA by enriched genomic library method (Yamamoto et al., 2002). Here we identify genetic diversity in 38 ecotypes of zoysiagrass (Z. matrella and Z. tenuifolia) from a group of southwest islands of Japan based on morphological characteristics and SSR markers

Um estudo sobre algoritmos genéticos.

Este trabalho apresenta uma descrição da metaheurística Algoritmos Genéticos. Como, onde e quando aplicar estes aplicar estes algoritmos são o alvo deste trabalho, assim comoas circunstâncias em que não se deve aplicá-los.bitstream/item/107617/1/Doc-5-2000-UM-ESTUDO-SOBRE-ALGORITMOS.pd