3,220 research outputs found
Optimal routing of military convoys through a road network
To wage a successful campaign, military units and materiel must be in position by the designated time. This thesis models the problem of moving military units and materiel in convoys through a road network as mathematical programming models. In particular, two models, linear and integer, are investigates. both models belong to the class of multicommodity, dynamic transshipment network problems. Based on prototypic GAMS implementations, they provide essentially the same answer. However, the linear model is easier to construct, takes less time to solve and allows for more flexible convoy routing.http://archive.org/details/optimalroutingof00leedMajor, Republic of Korea ArmyApproved for public release; distribution is unlimited
Scaling of cluster heterogeneity in percolation transitions
We investigate a critical scaling law for the cluster heterogeneity in
site and bond percolations in -dimensional lattices with . The
cluster heterogeneity is defined as the number of distinct cluster sizes. As an
occupation probability increases, the cluster size distribution evolves
from a monodisperse distribution to a polydisperse one in the subcritical
phase, and back to a monodisperse one in the supercritical phase. We show
analytically that diverges algebraically approaching the percolation
critical point as with the critical exponent
associated with the characteristic cluster size. Interestingly, its
finite-size-scaling behavior is governed by a new exponent where is the fractal dimension of the critical percolating
cluster and is the correlation length exponent. The corresponding scaling
variable defines a singular path to the critical point. All results are
confirmed by numerical simulations.Comment: 4 pages, 4 figure
Observation of chiral quantum-Hall edge states in graphene
In this study, we determined the chiral direction of the quantum-Hall (QH)
edge states in graphene by adopting simple two-terminal conductance
measurements while grounding different edge positions of the sample. The edge
state with a smaller filling factor is found to more strongly interact with the
electric contacts. This simple method can be conveniently used to investigate
the chirality of the QH edge state with zero filling factor in graphene, which
is important to understand the symmetry breaking sequence in high magnetic
fields (25 T).Comment: 3 pages, 3 figures. Appeared in AP
Dependence of quantum-Hall conductance on the edge-state equilibration position in a bipolar graphene sheet
By using four-terminal configurations, we investigated the dependence of
longitudinal and diagonal resistances of a graphene p-n interface on the
quantum-Hall edge-state equilibration position. The resistance of a p-n device
in our four-terminal scheme is asymmetric with respect to the zero point where
the filling factor () of the entire graphene vanishes. This resistance
asymmetry is caused by the chiral-direction-dependent change of the
equilibration position and leads to a deeper insight into the equilibration
process of the quantum-Hall edge states in a bipolar graphene system.Comment: 5 pages, 4 figures, will be published in PR
Thermoelectric Transport of Massive Dirac Fermions in Bilayer Graphene
Thermoelectric power (TEP) is measured in bilayer graphene for various
temperatures and charge-carrier densities. At low temperatures, measured TEP
well follows the semiclassical Mott formula with a hyperbolic dispersion
relation. TEP for a high carrier density shows a linear temperature dependence,
which demonstrates a weak electron-phonon interaction in the bilayer graphene.
For a low carrier density, a deviation from the Mott relation is observed at
high temperatures and is attributed to the low Fermi temperature in the bilayer
graphene. Oscillating TEP and the Nernst effect for varying carrier density,
observed in a high magnetic field, are qualitatively explained by the two
dimensionality of the system.Comment: published versio
Inelastic scattering in a monolayer graphene sheet; a weak-localization study
Charge carriers in a graphene sheet, a single layer of graphite, exhibit much
distinctive characteristics to those in other two-dimensional electronic
systems because of their chiral nature. In this report, we focus on the
observation of weak localization in a graphene sheet exfoliated from a piece of
natural graphite and nano-patterned into a Hall-bar geometry. Much stronger
chiral-symmetry-breaking elastic intervalley scattering in our graphene sheet
restores the conventional weak localization. The resulting carrier-density and
temperature dependence of the phase coherence length reveal that the
electron-electron interaction including a direct Coulomb interaction is the
main inelastic scattering factor while electron-hole puddles enhance the
inelastic scattering near the Dirac point.Comment: 12 pages, 3 figures, submitted to PR
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