23,927 research outputs found
Highly Optimized Tolerance: Robustness and Power Laws in Complex Systems
We introduce highly optimized tolerance (HOT), a mechanism that connects
evolving structure and power laws in interconnected systems. HOT systems arise,
e.g., in biology and engineering, where design and evolution create complex
systems sharing common features, including (1) high efficiency, performance,
and robustness to designed-for uncertainties, (2) hypersensitivity to design
flaws and unanticipated perturbations, (3) nongeneric, specialized, structured
configurations, and (4) power laws. We introduce HOT states in the context of
percolation, and contrast properties of the high density HOT states with random
configurations near the critical point. While both cases exhibit power laws,
only HOT states display properties (1-3) associated with design and evolution.Comment: 4 pages, 2 figure
Highly Optimized Tolerance: Robustness and Design in Complex Systems
Highly optimized tolerance (HOT) is a mechanism that relates evolving structure to power laws in interconnected systems. HOT systems arise where design and evolution create complex systems sharing common features, including (1) high efficiency, performance, and robustness to designed-for uncertainties, (2) hypersensitivity to design flaws and unanticipated perturbations, (3) nongeneric, specialized, structured configurations, and (4) power laws. We study the impact of incorporating increasing levels of design and find that even small amounts of design lead to HOT states in percolation
Power Laws, Highly Optimized Tolerance, and Generalized Source Coding
We introduce a family of robust design problems for complex systems in uncertain environments which are based on tradeoffs between resource allocations and losses. Optimized solutions yield the “robust, yet fragile” features of highly optimized tolerance and exhibit power law tails in the distributions of events for all but the special case of Shannon coding for data compression. In addition to data compression, we construct specific solutions for world wide web traffic and forest fires, and obtain excellent agreement with measured data
Applications of remote sensing in resource management in Nebraska
There are no author-identified significant results in this report
Stick-Slip Motion and Phase Transition in a Block-Spring System
We study numerically stick slip motions in a model of blocks and springs
being pulled slowly. The sliding friction is assumed to change dynamically with
a state variable. The transition from steady sliding to stick-slip is
subcritical in a single block and spring system. However, we find that the
transition is continuous in a long chain of blocks and springs. The size
distribution of stick-slip motions exhibits a power law at the critical point.Comment: 8 figure
A molecular dynamics simulation of DNA damage induction by ionizing radiation
We present a multi-scale simulation of early stage of DNA damages by the
indirect action of hydroxyl (OH) free radicals generated by electrons
and protons. The computational method comprises of interfacing the Geant4-DNA
Monte Carlo with the ReaxFF molecular dynamics software. A clustering method
was employed to map the coordinates of OH-radicals extracted from the
ionization track-structures onto nano-meter simulation voxels filled with DNA
and water molecules. The molecular dynamics simulation provides the time
evolution and chemical reactions in individual simulation voxels as well as the
energy-landscape accounted for the DNA-OH chemical reaction that is
essential for the first principle enumeration of hydrogen abstractions,
chemical bond breaks, and DNA-lesions induced by collection of ions in clusters
less than the critical dimension which is approximately 2-3 \AA. We show that
the formation of broken bonds leads to DNA base and backbone damages that
collectively propagate to DNA single and double strand breaks. For illustration
of the methodology, we focused on particles with initial energy of 1 MeV. Our
studies reveal a qualitative difference in DNA damage induced by low energy
electrons and protons. Electrons mainly generate small pockets of
OH-radicals, randomly dispersed in the cell volume. In contrast,
protons generate larger clusters along a straight-line parallel to the
direction of the particle. The ratio of the total DNA double strand breaks
induced by a single proton and electron track is determined to be 4
in the linear scaling limit. The tool developed in this work can be used in the
future to investigate the relative biological effectiveness of light and heavy
ions that are used in radiotherapy.Comment: 7 pages, 7 figures, accepted for publication in Physics in Medicine
and Biolog
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