26,995 research outputs found
Majority-vote model on (3,4,6,4) and (3^4,6) Archimedean lattices
On Archimedean lattices, the Ising model exhibits spontaneous ordering. Two
examples of these lattices of the majority-vote model with noise are considered
and studied through extensive Monte Carlo simulations. The order/disorder phase
transition is observed in this system. The calculated values of the critical
noise parameter are q_c=0.091(2) and q_c=0.134(3) for (3,4,6,4) and (3^4,6)
Archimedean lattices, respectively. The critical exponents beta/nu, gamma/nu
and 1/nu for this model are 0.103(6), 1.596(54), 0.872(85) for (3,4,6,4) and
0.114(3), 1.632(35), 0.978(104) for (3^4,6) Archimedean lattices. These results
differs from the usual Ising model results and the majority-vote model on
so-far studied regular lattices or complex networks. The effective
dimensionality of the system [D_{eff}(3,4,6,4)=1.802(55) and
D_{eff}(3^4,6)=1.860(34)] for these networks are reasonably close to the
embedding dimension two.Comment: 6 pages, 7 figures in 12 eps files, RevTex
A comparative analysis of XV-15 tiltrotor hover test data and WOPWOP predictions incorporating the fountain effect
Acoustic measurements from a hovering full scale XV-15 tilt rotor with the advanced technology blades are presented which show the directionality of fountain effect noise. Predicted acoustic directivity results are also presented which show agreement with the measured data. The aeroacoustic code, WOPWOP, was used in conjunction with a mathematical model which simulated the fountain recirculation aerodynamic effect on the rotor blade surface pressures. The predictions were used to identify the spike character in the measured data as fountain effect associated noise. The directivity of the fountain effect noise was observed to be dominant at the rear of the aircraft with increased intensities 45 degrees below the rotor disk planes
Average distance in growing trees
Two kinds of evolving trees are considered here: the exponential trees, where
subsequent nodes are linked to old nodes without any preference, and the
Barab\'asi--Albert scale-free networks, where the probability of linking to a
node is proportional to the number of its pre-existing links. In both cases,
new nodes are linked to nodes. Average node-node distance is
calculated numerically in evolving trees as dependent on the number of nodes
. The results for not less than a thousand are averaged over a thousand
of growing trees. The results on the mean node-node distance for large
can be approximated by for the exponential trees, and
for the scale-free trees, where the are constant. We
derive also iterative equations for and its dispersion for the exponential
trees. The simulation and the analytical approach give the same results.Comment: 6 pages, 3 figures, Int. J. Mod. Phys. C14 (2003) - in prin
Bose-Einstein condensation in complex networks
The evolution of many complex systems, including the world wide web, business
and citation networks is encoded in the dynamic web describing the interactions
between the system's constituents. Despite their irreversible and
non-equilibrium nature these networks follow Bose statistics and can undergo
Bose-Einstein condensation. Addressing the dynamical properties of these
non-equilibrium systems within the framework of equilibrium quantum gases
predicts that the 'first-mover-advantage', 'fit-get-rich' and
'winner-takes-all' phenomena observed in competitive systems are
thermodynamically distinct phases of the underlying evolving networks
Isolating Geometry in Weak Lensing Measurements
Given a foreground galaxy-density field or shear field, its cross-correlation
with the shear field from a background population of source galaxies scales
with the source redshift in a way that is specific to lensing. Such a
source-scaling can be exploited to effectively measure geometrical distances as
a function of redshift and thereby constrain dark energy properties, free of
any assumptions about the galaxy-mass/mass power spectrum (its shape, amplitude
or growth). Such a geometrical method can yield a ~ 0.03 - 0.07 f_{sky}^{-1/2}
measurement on the dark energy abundance and equation of state, for a
photometric redshift accuracy of dz ~ 0.01 - 0.05 and a survey with median
redshift of ~ 1. While these constraints are weaker than conventional weak
lensing methods, they provide an important consistency check because the
geometrical method carries less theoretical baggage: there is no need to assume
any structure formation model (e.g. CDM). The geometrical method is at the most
conservative end of a whole spectrum of methods which obtain smaller errorbars
by making more restrictive assumptions -- we discuss some examples. Our
geometrical approach differs from previous investigations along similar lines
in three respects. First, the source-scaling we propose to use is less
demanding on the photometric redshift accuracy. Second, the scaling works for
both galaxy-shear and shear-shear correlations. Third, we find that previous
studies underestimate the statistical errors associated with similar
geometrical methods, the origin of which is discussed.Comment: 13 pages, 4 figures, submitted to Ap
Recrystallization of epitaxial GaN under indentation
We report recrystallization of epitaxial (epi-) GaN(0001) film under
indentation.Hardness value is measured close to 10 GPa, using a Berkovich
indenter. Pop-in burst in the loading line indicates nucleation of dislocations
setting in plastic motion of lattice atoms under stress field for the
recrystallization process. Micro-Raman studies are used to identify the
recrystallization process. Raman area mapping indicates the crystallized
region. Phonon mode corresponding to E2(high) close to 570 cm-1 in the as-grown
epi-GaN is redshifted to stress free value close to 567 cm-1 in the indented
region. Evolution of A1(TO) and E1(TO) phonon modes are also reported to
signify the recrystallization process.Comment: 10 pages, 3 figures
The Discovery of a Spatially-Resolved Supernova Remnant in M31 with Chandra
Chandra observations of M31 allow the first spatially resolved X-ray image of
a supernova remnant (SNR) in an external spiral galaxy. CXOM31 J004327.7+411829
is a slightly elongated ring-shaped object with a diameter of ~11'' (42 pc). In
addition, the X-ray image hints that the chemical composition of the SNR is
spatial dependent. The X-ray spectrum of the SNR can be well fitted with a
Raymond-Smith model or a non-equilibrium ionization model. Depending on the
spectral model, the 0.3-7 keV luminosity is between 3.2x10^36 erg/s and
4.5x10^37 erg/s. The age of the SNR is estimated to be 3210-22300 years and the
number density of ambient gas is ~0.003-0.3 cm^-3. This suggests that the local
interstellar medium around the SNR is low.Comment: 5 pages, 3 figures; accepted for publication in ApJ
The Impact of Ice Layers on Gas Transport through Firn at the North Greenland Eemian Ice Drilling (Neem) Site, Greenland
Typically, gas transport through firn is modeled in the context of an idealized firn column. However, in natural firn, imperfections are present, which can alter transport dynamics and therefore reduce the accuracy of reconstructed climate records. For example, ice layers have been found in several firn cores collected in the polar regions. Here, we examined the effects of two ice layers found in a NEEM, Greenland firn core on gas transport through the firn. These ice layers were found to have permeability values of 3.0 and 4.0 × 10−10 m2, and are therefore not impermeable layers. However, the shallower ice layer was found to be significantly less permeable than the surrounding firn, and can therefore retard gas transport. Large closed bubbles were found in the deeper ice layer, which will have an altered gas composition than that expected because they were closed near the surface after the water phase was present. The bubbles in this layer represent 12% of the expected closed porosity of this firn layer after the firn-ice transition depth is reached, and will therefore bias the future ice core gas record. The permeability and thickness of the ice layers at the North Greenland Eemian Ice Drilling (NEEM) site suggest that they do not disrupt the firn-air concentration profiles and that they do not need to be accounted for in gas transport models at NEEM
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