41,102 research outputs found
Diverse Supernova Sources for the r-Process and Abundances in Metal-Poor Stars
The dispersion and mean trends of r-process abundances in metal-poor stars
are discussed based on a model of diverse supernova sources for the r-process.
This model is unique in that its key parameters are inferred from solar system
data independent of stellar observations at low metallicities. It is shown that
this model provides a good explanation for the observed dispersion and mean
trend of Eu abundances over -3 < [Fe/H] < -1. It is also shown that this model
provides a means to discuss r-abundances in general. For example, the Ag
abundance in any metal-poor star with observed Eu and Fe abundances can be
calculated from the model. This approach is demonstrated with success for two
stars and can be further tested by future Ag data. The dispersion and mean
trend of Ag abundances in metal-poor stars are also calculated for comparison
with future observations.Comment: 4 pages, 2 figures, to appear in ApJL (submitted February 1, 2001
Neutrino-Induced Fission and r-Process Nucleosynthesis
An r-process scenario with fission but no fission cycling is considered to
account for the observed abundance patterns of neutron-capture elements in
ultra-metal-poor stars. It is proposed that neutrino reactions play a crucial
role in inducing the fission of the progenitor nuclei after the r-process
freezes out in Type II Supernovae. To facilitate neutrino-induced fission, the
proposed r-process scenario is restricted to occur in a low-density environment
such as the neutrino-driven wind from the neutron star. Further studies to
develop this scenario are emphasized.Comment: 11 pages, 2 figures, to appear in ApJ
A survey on cyber security for smart grid communications
A smart grid is a new form of electricity network with high fidelity power-flow control, self-healing, and energy reliability and energy security using digital communications and control technology. To upgrade an existing power grid into a smart grid, it requires significant dependence on intelligent and secure communication infrastructures. It requires security frameworks for distributed communications, pervasive computing and sensing technologies in smart grid. However, as many of the communication technologies currently recommended to use by a smart grid is vulnerable in cyber security, it could lead to unreliable system operations, causing unnecessary expenditure, even consequential disaster to both utilities and consumers. In this paper, we summarize the cyber security requirements and the possible vulnerabilities in smart grid communications and survey the current solutions on cyber security for smart grid communications. © 2012 IEEE
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