Reply to [arXiv:1105.5147] "Are GRB 090423 and Similar Bursts due to Superconducting Cosmic Strings?"

The GRB outflow driven by superconducting cosmic strings is likely to be an arc rather than a usually-considered spherical cap. In such a case, the afterglows of the cosmic string GRBs could be basically consistent with the observation of the high-redshift GRBs.Comment: 2 pages, 1 figure, to appear in Phys. Rev. Let

Diverse Temporal Properties of GRB Afterglow

The detection of delayed X-ray, optical and radio emission, "afterglow", associated with $\gamma$-ray bursts (GRBs) is consistent with fireball models, where the emission are produced by relativistic expanding blast wave, driven by expanding fireball at cosmogical distances. The emission mechanisms of GRB afterglow have been discussed by many authors and synchrotron radiation is believed to be the main mechanism. The observations show that the optical light curves of two observed gamma-ray bursts, GRB970228 and GRB GRB970508, can be described by a simple power law, which seems to support the synchrotron radiation explanation. However, here we shall show that under some circumstances, the inverse Compton scattering (ICS) may play an important role in emission spectrum and this may influence the temporal properties of GRB afterglow. We expect that the light curves of GRB afterglow may consist of multi-components, which depends on the fireball parameters.Comment: Latex, no figures, minor correctio

A PROCESS STUDY OF EFFECTS OF GSS AND TASK TYPE ON INFORMATIONAL AND NORMATIVE INFLUENCE IN SMALL GROUPS

This research examines the effects of GSS and task type on informational and normative influence in small groups by analyzing group process. It extends Kaplan and Miller\u27 s research on task type and informational and normative influence in small groups in an unsupported setting to a GSS setting. The two tasks used are an intellective task and a preference task, and the two support levels are unsupported baseline and GSS support. The findings show that (1) the mode of influence that predominates in group discussion depends on task type, but the degree of dominance is moderated by support level, and (2) GSS has the potential to encourage the use of informational influence in intellective task groups and discourage the use of normative influence in preference task groups. These findings suggest that task type may have significant effects on influence behavior in small groups and a GSS may have some beneficial effects for certain task types but not for others. The paper concludes with some suggestions for further research

Crossing of the Phantom Divided Barrier with Lorentz Invariance Violating Fields

We study possible crossing of the phantom divided barrier in a Lorentz invariance violating dark energy model. Lorentz invariance violation which is achieved by introducing a vector field in the action, incorporates directly in the dynamics of the scalar field and equation of state. This interesting feature allows us to study phantom divided barrier crossing in the context of Lorentz invariance violation. We show that for suitable choice of parameter space, equation of state can cross phantom divided barrier just by one scalar field and Lorentz violating vector field controls this crossing.Comment: 14 pages, 4 figures, Revised and References added, Accepted for Publication in Europhysics Letter

Is GRO J1744-28 a Strange Star?

The unusal hard x-ray burster GRO J1744-28 recently discovered by the Compton Gamma-ray Observatory (GRO) can be modeled as a strange star with a dipolar magnetic field $\le 10^{11}$Gauss. When the accreted mass of the star exceeds some critical mass, its crust may break, resulting in conversion of the accreted matter into strange matter and release of energy. Subsequently, a fireball may form and expand relativistically outward. The expanding fireball may interact with the surrounding interstellar medium, causing its kinetic energy to be radiated in shock waves, producing a burst of x-ray radiation. The burst energy, duration, interval and spectrum derived from such a model are consistent with the observations of GRO J1744-28.Comment: Latex, has been published in SCIENCE, Vol. 280, 40

The topological glass in ring polymers

We study the dynamics of concentrated, long, semi-flexible, unknotted and unlinked ring polymers embedded in a gel by Monte Carlo simulation of a coarse-grained model. This involves the ansatz that the rings compactify into a duplex structure where they can be modelled as linear polymers. The classical polymer glass transition involves a rapid loss of microscopic freedom within the polymer molecule as the temperature is reduced toward Tg. Here we are interested in temperatures well above Tg where the polymers retain high microscopic mobility. We analyse the slowing of stress relaxation originating from inter-ring penetrations (threadings). For long polymers an extended network of quasi-topological penetrations forms. The longest relaxation time appears to depend exponentially on the ring polymer contour length, reminiscent of the usual exponential slowing (e.g., with temperature) in classical glasses. Finally, we discuss how this represents a universality class for glassy dynamics

Spectrum of low-lying s3QQˉs^{3}Q\bar{Q} configurations with negative parity

Spectrum of low-lying five-quark configurations with strangeness quantum number $S=-3$ and negative parity is studied in three kinds of constituent quark models, namely the one gluon exchange, Goldstone Boson exchange, and instanton-induced hyperfine interaction models, respectively. Our numerical results show that the lowest energy states in all the three employed models are lying at $\sim$1800 MeV, about 200 MeV lower than predictions of various quenched three-quark models. In addition, it is very interesting that the state with the lowest energy in one gluon exchange model is with spin 3/2, but 1/2 in the other two models.Comment: Version published in Phys. Rev.

Strong Pinning Enhancement in MgB2 Using Very Small Dy2O3 Additions

0.5 to 5.0 wt.% Dy2O3 was in-situ reacted with Mg + B to form pinned MgB2. While Tc remained largely unchanged, Jc was strongly enhanced. The best sample (only 0.5 wt.% Dy2O3) had a Jc of 6.5 x 10^5 A/cm^2 at 6K, 1T and 3.5 x 10^5 A/cm^2 at 20K, 1T, around a factor of 4 higher compared to the pure sample, and equivalent to hot-pressed or nano-Si added MgB2 at below 1T. Even distributions of nano-scale precipitates of DyB4 and MgO were observed within the grains. The room temperature resistivity decreased with Dy2O3 indicative of improved grain connectivity.Comment: 13 pages, 4 figures and 1 tabl

Effect of carbon nanotube doping on critical current density of MgB2 superconductor

The effect of doping MgB2 with carbon nanotubes on transition temperature, lattice parameters, critical current density and flux pinning was studied for MgB2-xCx with x = 0, 0.05, 0.1, 0.2 and 0.3. The carbon substitution for B was found to enhance Jc in magnetic fields but depress Tc. The depression of Tc, which is caused by the carbon substitution for B, increases with increasing doping level, sintering temperature and duration. By controlling the extent of the substitution and addition of carbon nanotubes we can achieve the optimal improvement on critical current density and flux pinning in magnetic fields while maintaining the minimum reduction in Tc. Under these conditions, Jc was enhanced by two orders of magnitude at 8T and 5K and 7T and 10K. Jc was more than 10,000A/cm2 at 20K and 4T and 5K and 8.5T, respectively

Magnetic field switching in parallel quantum dots

We show that the Coulomb blockade in parallel dots pierced by magnetic flux $\Phi$ completely blocks the resonant current for any value of $\Phi$ except for integer multiples of the flux quantum $\Phi_0$. This non-analytic (switching) dependence of the current on $\Phi$ arises only when the dot states that carry the current are of the same energy. The time needed to reach the steady state, however, diverges when $\Phi\to n\Phi_0$.Comment: additional explanations added, Europhysics Letters, in pres