2,033 research outputs found
Reconciling long-term cultural diversity and short-term collective social behavior
An outstanding open problem is whether collective social phenomena occurring
over short timescales can systematically reduce cultural heterogeneity in the
long run, and whether offline and online human interactions contribute
differently to the process. Theoretical models suggest that short-term
collective behavior and long-term cultural diversity are mutually excluding,
since they require very different levels of social influence. The latter
jointly depends on two factors: the topology of the underlying social network
and the overlap between individuals in multidimensional cultural space.
However, while the empirical properties of social networks are well understood,
little is known about the large-scale organization of real societies in
cultural space, so that random input specifications are necessarily used in
models. Here we use a large dataset to perform a high-dimensional analysis of
the scientific beliefs of thousands of Europeans. We find that inter-opinion
correlations determine a nontrivial ultrametric hierarchy of individuals in
cultural space, a result unaccessible to one-dimensional analyses and in
striking contrast with random assumptions. When empirical data are used as
inputs in models, we find that ultrametricity has strong and counterintuitive
effects, especially in the extreme case of long-range online-like interactions
bypassing social ties. On short time-scales, it strongly facilitates a
symmetry-breaking phase transition triggering coordinated social behavior. On
long time-scales, it severely suppresses cultural convergence by restricting it
within disjoint groups. We therefore find that, remarkably, the empirical
distribution of individuals in cultural space appears to optimize the
coexistence of short-term collective behavior and long-term cultural diversity,
which can be realized simultaneously for the same moderate level of mutual
influence
The relative wavelength independence of IR lags in active galactic nuclei: implications for the distribution of the hot dust
We show that, contrary to simple predictions, most AGNs show at best only a
small increase of lags in the J, H, K, and L bands with increasing wavelength.
We suggest that a possible cause of this near simultaneity of the variability
from the near-IR to the mid-IR is that the hot dust is in a hollow bi-conical
outflow of which we only see the near side. Although most AGNs show near
simultaneity of IR variability, there was at least one epoch when NGC 4151
showed the sharply increasing IR lag with the increase of the wavelength. This
behaviour might also be present in GQ Comae. We discuss these results briefly.
The relative wavelength independence of IR lags simplifies the use of IR lags
for estimating cosmological parameters.Comment: 6 pages, 5 figures, for the Odessa Astronomical Publicatio
Generator Matrix Elements For II
Basis states and generator matrix elements are given for the generic
representation of in an basis.Comment: Latex, 17 pages, one figure using epsf published in J. Phys. A: Math.
Gen 28 (1995) 2581-258
Variability of Active Galactic Nuclei from the Optical to X-ray Regions
Some progress in understanding AGN variability is reviewed. Reprocessing of
X-ray radiation to produce significant amounts of longer-wavelength continua
seems to be ruled out. In some objects where there has been correlated X-ray
and optical variability, the amplitude of the optical variability has exceeded
the amplitude of X-ray variability. We suggest that accelerated particles
striking material could be linking X-ray and optical variability (as in
activity in the solar chromosphere). Beaming effects could be significant in
all types of AGN. The diversity in optical/X-ray relationships at different
times in the same object, and between different objects, might be explained by
changes in geometry and directions of motion relative to our line of sight.
Linear shot-noise models of the variability are ruled out; instead there must
be large-scale organization of variability. Variability occurs on
light-crossing timescales rather than viscous timescales and this probably
rules out the standard Shakura-Sunyaev accretion disk. Radio-loud and
radio-quiet AGNs have similar continuum shapes and similar variability
properties. This suggests similar continuum origins and variability mechanisms.
Despite their extreme X-ray variability, narrow-line Seyfert 1s (NLS1s) do not
show extreme optical variability.Comment: Invited talk given at Euro Asian Astronomical Society meeting in
Moscow, June 2002. 20 pages, 4 figures. References update
Spectrophotometry of 2 complete samples of flat radio spectrum quasars
Spectrophotometry of two complete samples of flat-spectrum radio quasars show that for these objects there is a strong correlation between the equivalent width of the CIV wavelength 1550 emission line and the luminosity of the underlying continuum. Assuming Friedmann cosmologies, the scatter in this correlation is a minimum for q (sub o) is approximately 1. Alternatively, luminosity evolution can be invoked to give compact distributions for q (sub o) is approximately 0 models. A sample of Seyfert galaxies observed with IUE shows that despite some dispersion the average equivalent width of CIV wavelength 1550 in Seyfert galaxies is independent of the underlying continuum luminosity. New redshifts for 4 quasars are given
Hole polaron formation and migration in olivine phosphate materials
By combining first principles calculations and experimental XPS measurements,
we investigate the electronic structure of potential Li-ion battery cathode
materials LiMPO4 (M=Mn,Fe,Co,Ni) to uncover the underlying mechanisms that
determine small hole polaron formation and migration. We show that small hole
polaron formation depends on features in the electronic structure near the
valence-band maximum and that, calculationally, these features depend on the
methodology chosen for dealing with the correlated nature of the
transition-metal d-derived states in these systems. Comparison with experiment
reveals that a hybrid functional approach is superior to GGA+U in correctly
reproducing the XPS spectra. Using this approach we find that LiNiPO4 cannot
support small hole polarons, but that the other three compounds can. The
migration barrier is determined mainly by the strong or weak bonding nature of
the states at the top of the valence band, resulting in a substantially higher
barrier for LiMnPO4 than for LiCoPO4 or LiFePO4
Interpretation of IR variability of AGNs in the hollow bi-conical dust outflow model
We show that, contrary to simple predictions, most AGNs show at best only a
small increase of lags with increasing wavelength in the J, H, K, and L bands .
We suggest that a possible cause of this near simultaneity of the variability
from the near-IR to the mid-IR is that the hot dust is in a hollow bi-conical
outflow of which we preferentially see the near side. In the proposed model
sublimation or re-creation of dust (with some delay relative luminosity
variations) along our line of sight in the hollow cone could be a factor in
explaining the changing look phenomenon of AGNs. Variations in the dust
obscuration can help explain changes in relationship of H-beta time delay on
Luv variability. The relative wavelength independence of IR lags simplifies the
use of IR lags for estimating cosmological parameters.Comment: 5 pages, 1 figure, IAU Sym 37
First-principles prediction of a decagonal quasicrystal containing boron
We interpret experimentally known B-Mg-Ru crystals as quasicrystal
approximants. These approximant structures imply a deterministic decoration of
tiles by atoms that can be extended quasiperiodically. Experimentally observed
structural disorder corresponds to phason (tile flip) fluctuations.
First-principles total energy calculations reveal that many distinct tilings
lie close to stability at low temperatures. Transfer matrix calculations based
on these energies suggest a phase transition from a crystalline state at low
temperatures to a high temperature state characterized by tile fluctuations. We
predict BMgRu forms a decagonal quasicrystal that is
metastable at low temperatures and may be thermodynamically stable at high
temperatures.Comment: 4 pages, 3 figures, submitted to Phys. Rev. Let
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