2,266 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
Providing adhesion for a miniture mobile intra-abdominal device based on biomimetic principles
This paper investigates the surface adhesion
characteristics required for a miniature mobile device to
move around the abdominal cavity. Such a device must
be capable of adhering to the tissue lining and move
freely across the upper surface of the insufflated
abdomen. Accordingly, the potential of utilising bioinspired
solutions to facilitate wet adhesion is assessed
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
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
Reverberation Mapping Results from MDM Observatory
We present results from a multi-month reverberation mapping campaign
undertaken primarily at MDM Observatory with supporting observations from
around the world. We measure broad line region (BLR) radii and black hole
masses for six objects. A velocity-resolved analysis of the H_beta response
shows the presence of diverse kinematic signatures in the BLR.Comment: To appear in the Proceedings of the IAU Symposium No. 267:
Co-Evolution of Central Black Holes and Galaxies, Rio de Janeiro, 200
Unexpected benefits of pre-university skills training for A-level students
First-year undergraduates can find the transition from the prescriptive learning environment at school to one of self-directed learning at university, a considerable challenge. A Pre-university Skills Course (PSC) was developed to address this issue by preparing sixth formers for the university learning style. It was piloted with students in the year prior to A-level examinations at a selective state-funded school in East Anglia. The present paper examines the effect of the course on the students’ A-level tariff. Chi-squared analysis of A-level grades of students with comparable GCSE results, indicate that students who undertook the PSC performed significantly better in their A-level results than those who did not. These data demonstrate how skills training might improve A-level performance and assist in the transition to university
Eddy genesis and manipulation in plane laminar shear flow
Eddy formation and presence in a plane laminar shear flow configuration consisting of two infinitely long plates orientated parallel to each other is investigated theoretically. The upper plate, which is planar, drives the flow; the lower one has a sinusoidal profile and is fixed. The governing equations are solved via a full finite element formulation for the general case and semi-analytically at the Stokes flow limit. The effects of varying geometry (involving changes in the mean plate separation or the amplitude and wavelength of the lower plate) and inertia are explored separately. For Stokes flow and varying geometry, excellent agreement between the two methods of solution is found. Of particular interest with regard to the flow structure is the importance of the clearance that exists between the upper plate and the tops of the corrugations forming the lower one. When the clearance is large, an eddy is only present at sufficiently large amplitudes or small wavelengths.
However, as the plate clearance is reduced, a critical value is found which triggers the formation of an eddy in an otherwise fully attached flow for any finite amplitude and arbitrarily large wavelength. This is a precursor to the primary eddy to be expected in the lid-driven cavity flow which is formed in the limit of zero clearance between the plates. The influence of the flow driving mechanism is assessed by comparison with corresponding solutions for the case of gravity-driven fluid films flowing over an undulating substrate. When inertia is present, the flow generally becomes asymmetrical. However, it is found that for large mean plate separations the flow local to the lower plate becomes effectively decoupled from the inertia dominated overlying flow if the wavelength of the lower plate is sufficiently small. In such cases the local flow retains its symmetry. A local Reynolds number based on the wavelength is shown to be useful in characterising these large-gap flows. As the mean plate separation is reduced, the form of the asymmetry caused by inertia changes, and becomes strongly dependent on the plate separation. For lower plate wavelengths which do not exhibit a cinematically induced secondary eddy, an inertially induced secondary eddy can be created if the mean plate separation is sufficiently small and the global Reynolds number sufficiently large
Mergers in Double-Peaked [O III] Active Galactic Nuclei
As a natural consequence of galaxy mergers, binary active galactic nuclei
(AGNs) should be commonplace. Nevertheless, observational confirmations are
rare, especially for binaries with separations less than ten kpc. Such a system
may show two sets of narrow emission lines in a single spectrum owing to the
orbital motion of the binary. We have obtained high-resolution near-infrared
images of 50 double-peaked [O III] 5007 AGNs with the Keck II laser guide star
adaptive optics system. The Sloan Digital Sky Survey sample is compiled from
the literature and consists of 17 type-1 AGNs between 0.18 < z < 0.56 and 33
type-2 AGNs between 0.03 < z < 0.24. The new images reveal eight type-1 and
eight type-2 sources that are apparently undergoing mergers. These are strong
candidates of kpc-scale binary AGNs, because they show multiple components
separated between 0.6 and 12 kpc and often disturbed morphologies. Because most
of the type-1s are at higher redshifts than the type-2s, the higher merger
fraction of type-1s (47+/-20%) compared to that of type-2s (24+/-10%) can be
attributed to the general evolution of galaxy merger fraction with redshift.
Furthermore, we show that AGN mergers are outliers of the M_BH-sigma relation
because of over-estimated stellar velocity dispersions, illustrating the
importance of removing mergers from the samples defining the M_BH-sigma
relations. Finally, we find that the emission-line properties are
indistinguishable for spatially resolved and unresolved sources, emphasizing
that scenarios involving a single AGN can produce the same double-peaked line
profiles and they account for at least 70% of the double-peaked [O III] AGNs.Comment: ApJ accepted with major revisions, main results unchanged. 7 pages, 5
figures, 1 table, emulateapj styl
Collective dynamics of liquid aluminum probed by Inelastic X-ray Scattering
An inelastic X-ray scattering experiment has been performed in liquid
aluminum with the purpose of studying the collective excitations at wavevectors
below the first sharp diffraction peak. The high instrumental resolution (up to
1.5 meV) allows an accurate investigation of the dynamical processes in this
liquid metal on the basis of a generalized hydrodynamics framework. The
outcoming results confirm the presence of a viscosity relaxation scenario ruled
by a two timescale mechanism, as recently found in liquid lithium.Comment: 8 pages, 7 figure
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