Bipolar Transistor Based on Graphane

Graphane is a semiconductor with an energy gap, obtained from hydrogenation of the two-dimensional grapheme sheet. Together with the two-dimensional geometry, unique transport features of graphene, and possibility of doping graphane, p and n regions can be defined so that p-n junctions become feasible with small reverse currents. Our recent analysis has shown that an ideal I-V characteristic for this type of junctions may be expected. Here, we predict the behavior of bipolar juncrion transistors based on graphane. Profiles of carriers and intrinsic parameters of the graphane transistor are calculated and discussed

Comment on "Mass and K Lambda coupling of N*(1535)"

It is argued in [1] that when the strong coupling to the K Lambda channel is considered, Breit-Wigner mass of the lightest orbital excitation of the nucleon N(1535) shifts to a lower value. The new value turned out to be smaller than the mass of the lightest radial excitation N(1440), which effectively solved the long-standing problem of conventional constituent quark models. In this Comment we show that it is not the Breit-Wigner mass of N(1535) that is decreased, but its bare mass. [1] B. C. Liu and B. S. Zou, Phys. Rev. Lett. 96, 042002 (2006).Comment: 3 pages, comment on "Mass and K Lambda coupling of N*(1535)", B. C. Liu and B. S. Zou, Phys. Rev. Lett. 96, 042002 (2006

Soft gamma repeaters outside the Local group

We propose that the best sites to search for SGRs outside the Local group are galaxies with active massive star formation. Different possibilities to observe SGR activity from these sites are discussed. In particular we searched for giant flares from nearby galaxies ($\sim 2$ -- 4 Mpc) M82, M83, NGC 253, and NGC 4945 in the BATSE data. No candidates alike giant SGR flares were found. The absence of such detections implies that the rate of giant flares with energy release in the initial spike above $0.5 \cdot 10^{44}$ erg is less then 1/25 yr$^{-1}$ in our Galaxy. However, hyperflares similar to the one of 27 December 2004 can be observed from larger distances. Nevertheless, we do not see any significant excess of short GRBs from the Virgo galaxy cluster and from galaxies Arp 299 and NGC 3256 with extremely high star formation rate. This implies that the galactic rate of hyperflares with energy release $\sim 10^{46}$ erg is less than $\sim 10^{-3}$ yr$^{-1}$. With this constraint the fraction of possible extragalactic SGR hyperflares among BATSE short GRBs should not exceed few percents. We present a list of short GRBs coincident with galaxies mentioned above, and discuss the possibility that some of them are SGR giant flares. We propose that the best target for observations of extragalactic SGR flares by {\it Swift} is the Virgo cluster.Comment: 14 pages with 3 figures; accepted to MNRAS (final version