10,085 research outputs found
On Source Density Evolution of Gamma-ray Bursts
Recent optical afterglow observations of gamma-ray bursts indicate a setting
and distance scale that many relate to star-formation regions. In this paper,
we use and a set of artificial trigger thresholds to probe
several potential GRB source density evolutionary scenarios. In particular, we
compare a uniform subset of BATSE 4B data to cosmological scenarios where GRBs
evolve as the comoving density, the star formation rate, the QSO rate, and the
SN Type Ic rate. Standard candle bursts with power-law spectra and a universe
without vacuum energy were assumed. Our results significantly favor a comoving
density model, implying that GRB source density evolution is weaker than
expected in these evolutionary scenarios. GRB density might still follow
star-formation rates given proper concurrent GRB luminosity evolution,
significant beaming, significant error in standard candle assumptions, or were
a significant modification of star formation rate estimates to occur.Comment: 12 pages, 4 figures, accepted by Ap
Watermarking FPGA Bitfile for Intellectual Property Protection
Intellectual property protection (IPP) of hardware designs is the most important requirement for many Field Programmable Gate Array (FPGA) intellectual property (IP) vendors. Digital watermarking has become an innovative technology for IPP in recent years. Existing watermarking techniques have successfully embedded watermark into IP cores. However, many of these techniques share two specific weaknesses: 1) They have extra overhead, and are likely to degrade performance of design; 2) vulnerability to removing attacks. We propose a novel watermarking technique to watermark FPGA bitfile for addressing these weaknesses. Experimental results and analysis show that the proposed technique incurs zero overhead and it is robust against removing attacks
Effects of Cutoff Functions of Tersoff Potentials on Molecular Dynamics Simulations of Thermal Transport
Past molecular dynamics studies of thermal transport have predominantly used
Stillinger-Weber potentials. As materials continuously shrink, their properties
increasingly depend on defect and surface effects. Unfortunately,
Stillinger-Weber potentials are best used for diamond-cubic-like bulk crystals.
They cannot represent the energies of many metastable phases, nor can they
accurately predict the energetics of defective and surface regions. To study
nanostructured materials, where these regions can dominate thermal transport,
the accuracy of Tersoff potentials in representing these structures is more
desirable. Based upon an analysis of thermal transport in a GaN system, we
demonstrate that the cutoff function of the existing Tersoff potentials may
lead to problems in determining the thermal conductivity. To remedy this issue,
improved cutoff schemes are proposed and evaluated
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