A numerical study of the r-mode instability of rapidly rotating nascent neutron stars

The first results of numerical analysis of classical r-modes of {\it rapidly} rotating compressible stellar models are reported. The full set of linear perturbation equations of rotating stars in Newtonian gravity are numerically solved without the slow rotation approximation. A critical curve of gravitational wave emission induced instability which restricts the rotational frequencies of hot young neutron stars is obtained. Taking the standard cooling mechanisms of neutron stars into account, we also show the `evolutionary curves' along which neutron stars are supposed to evolve as cooling and spinning-down proceed. Rotational frequencies of $1.4M_{\odot}$ stars suffering from this instability decrease to around 100Hz when the standard cooling mechanism of neutron stars is employed. This result confirms the results of other authors who adopted the slow rotation approximation.Comment: 4 pages, 2 figures; MNRAS,316,L1(2000

Exploring differences in response to treatment with peginterferon alpha 2a (40kD) and ribavirin in chronic hepatitis C between genotypes 2 and 3

Chronic hepatitis C virus (HCV) infections with genotype 2 or 3 are associated with favourable sustained virologic response (SVR) rates. However, genotype 3 may respond less well. We reassessed all treatment-naive patients with genotype 2 and 3 participating in a large expanded-access, non-randomized, open-label trial, evaluating 180μg pegylated interferon (peg-IFN) alpha-2a (40kD) once weekly and 800 mg/day ribavirin for 24–48 weeks. Factors measured prior to initiation of antiviral therapy were considered in the multiple logistic regression model for predicting SVR. In total, 180 patients were analysed of which 72 (40%) were infected by genotype 2 and 108 (60%) genotype 3. The baseline characteristics between patients infected by genotype 2 or 3 were no different including the distribution of hepatic fibrosis stages by METAVIR score. Overall SVR was lower in those patients infected with genotype 3. The significant multivariate predictors of lack of SVR were hepatic fibrosis (P = 0.014) and genotype 3 (P = 0.030). The negative impact of cirrhosis (METAVIR score F4) on treatment response was more evident among subjects with genotype 3 than those with genotype 2 (P = 0.027). There is significant interaction between cirrhosis and genotype 3 leading to a poor antiviral response in such patients requiring an alternate management strategy. This finding should be confirmed in a larger population

Researches in Japan on heavy ion inertial fusion

Recent research activities in Japan are presented in this paper in heavy ion inertial fusion (HIF) [1]: shown are particle accelerator developments, beam dynamics researches, interaction between heavy ions and target materials, ion source developments, and illumination schemes of heavy ion beams (HIBs) in HIF..

Mechanical Properties of End-crosslinked Entangled Polymer Networks using Sliplink Brownian Dynamics Simulations

The mechanical properties of a polymeric network containing both crosslinks and sliplinks (entanglements) are studied using a multi-chain Brownian dynamics simulation. We coarse-grain at the level of chain segments connecting consecutive nodes (cross- or sliplinks), with particular attention to the Gaussian statistics of the network. Affine displacement of nodes is not imposed: their displacement as well as sliding of monomers through sliplinks is governed by force balances. The simulation results of stress in uniaxial extension and the full stress tensor in simple shear including the (non-zero) second normal stress difference are presented for monodisperse chains with up to 18 entanglements between two crosslinks. The cases of two different force laws of the subchains (Gaussian chains and chains with finite extensibility) for two different numbers of monomers in a subchain (no = 50 and no = 100) are examined. It is shown that the additivity assumption of slip- and crosslink contribution holds for sufficiently long chains with two or more entanglements, and that it can be used to construct the strain response of a network of infinitely long chains. An important consequence is that the contribution of sliplinks to the small-strain shear modulus is about ⅔ of the contribution of a crosslink

Numerical evolution of secular bar-mode instability induced by the gravitational radiation reaction in rapidly rotating neutron stars

The evolution of a nonaxisymmetric bar-mode perturbation of rapidly rotating stars due to a secular instability induced by gravitational wave emission is studied in post-Newtonian simulations taking into account gravitational radiation reaction. A polytropic equation of state with the polytropic index $n=1$ is adopted. The ratio of the rotational kinetic energy to the gravitational potential energy $T/|W|$ is chosen in the range between 0.2 and 0.26. Numerical simulations were performed until the perturbation grows to the nonlinear regime, and illustrate that the outcome after the secular instability sets in is an ellipsoidal star of a moderately large ellipticity \agt 0.7. A rapidly rotating protoneutron star may form such an ellipsoid, which is a candidate for strong emitter of gravitational waves for ground-based laser interferometric detectors. A possibility that effects of magnetic fields neglected in this work may modify the growth of the secular instability is also mentioned.Comment: PRD, accepted for publicatio

Female preference for blue in Japan blue guppies (Poecilia reticulata)

Guppies (Poecilia reticulata) are widely used as a model species in mate choice studies. Although native to South America, guppies have been introduced to natural water bodies in disparate regions of the globe. Here, for the first time, we examine guppies from one such introduced population in Japan where males have evolved a predominantly blue color pattern. Previous studies of wild-type guppies have shown blue to play a relatively minor role in the mate choice decisions of females compared to other traits, such as orange, and the importance of blue is not universally supported by all studies. The Japanese population therefore presents an ideal opportunity to re-examine the potential significance of blue as a mate choice cue in guppies. Mate choice experiments, in which female Japan blue guppies were given a choice between pairs of males that differed in their area of blue coloration but were matched for other traits, revealed that females prefer males with proportionately larger amounts of blue in their color patterns. We discuss possible factors, including sexual and ecological selection, which may have led to the evolution of unusually large areas of blue at the expense of other colors in Japan blue guppies. However, further studies are needed to distinguish between these scenarios.Web of Scienc

A Sensory Bias Has Triggered the Evolution of Egg-Spots in Cichlid Fishes

Although, generally, the origin of sex-limited traits remains elusive, the sensory exploitation hypothesis provides an explanation for the evolution of male sexual signals. Anal fin egg-spots are such a male sexual signal and a key characteristic of the most species-rich group of cichlid fishes, the haplochromines. Males of about 1500 mouth-brooding species utilize these conspicuous egg-dummies during courtship – apparently to attract females and to maximize fertilization success. Here we test the hypothesis that the evolution of haplochromine egg-spots was triggered by a pre-existing bias for eggs or egg-like coloration. To this end, we performed mate-choice experiments in the basal haplochromine Pseudocrenilabrus multicolor, which manifests the plesiomorphic character-state of an egg-spot-less anal fin. Experiments using computer-animated photographs of males indeed revealed that females prefer images of males with virtual (‘in-silico’) egg-spots over images showing unaltered males. In addition, we tested for color preferences (outside a mating context) in a phylogenetically representative set of East African cichlids. We uncovered a strong preference for yellow, orange or reddish spots in all haplochromines tested and, importantly, also in most other species representing more basal lines. This pre-existing female sensory bias points towards high-quality (carotenoids-enriched) food suggesting that it is adaptive