3,031 research outputs found
Assortative Mixing Equilibria in Social Network Games
It is known that individuals in social networks tend to exhibit homophily
(a.k.a. assortative mixing) in their social ties, which implies that they
prefer bonding with others of their own kind. But what are the reasons for this
phenomenon? Is it that such relations are more convenient and easier to
maintain? Or are there also some more tangible benefits to be gained from this
collective behaviour?
The current work takes a game-theoretic perspective on this phenomenon, and
studies the conditions under which different assortative mixing strategies lead
to equilibrium in an evolving social network. We focus on a biased preferential
attachment model where the strategy of each group (e.g., political or social
minority) determines the level of bias of its members toward other group
members and non-members. Our first result is that if the utility function that
the group attempts to maximize is the degree centrality of the group,
interpreted as the sum of degrees of the group members in the network, then the
only strategy achieving Nash equilibrium is a perfect homophily, which implies
that cooperation with other groups is harmful to this utility function. A
second, and perhaps more surprising, result is that if a reward for inter-group
cooperation is added to the utility function (e.g., externally enforced by an
authority as a regulation), then there are only two possible equilibria,
namely, perfect homophily or perfect heterophily, and it is possible to
characterize their feasibility spaces. Interestingly, these results hold
regardless of the minority-majority ratio in the population.
We believe that these results, as well as the game-theoretic perspective
presented herein, may contribute to a better understanding of the forces that
shape the groups and communities of our society
Imaging of vascular remodeling after simulated thoracoabdominal aneurysm repair
ObjectiveA better understanding of the response of the spinal cord blood supply to segmental artery (SA) sacrifice should help minimize the risk of paraplegia after both open and endovascular repair of thoracoabdominal aortic (TAA) aneurysms.MethodsTwelve female juvenile Yorkshire pigs were randomized into 3 groups and perfused with a barium–latex solution. Pigs in group 1 (control) had infusion without previous intervention. Pigs in group 2 were infused 48 hours after ligation of all SAs (T4-L5) and those in group 3 at 120 hours after ligation. Postmortem computed tomographic scanning of the entire pig enabled overall comparisons and measurement of vessel diameters in the spinal cord circulation.ResultsWe ligated 14.5 ± 0.8 SAs: all filled retrograde to the ligature. Paraplegia occurred in 38% of operated pigs. A significant increase in the mean diameter of the anterior spinal artery (ASA) was evident after SA sacrifice (P < .0001 for 48 hours and 120 hours). The internal thoracic and intercostal arteries also increased in diameter. Quantitative assessment showed an increase in vessel density 48 hours after ligation of SAs, reflected by an obvious increase in small collateral vessels seen on 3-dimensional reconstructions of computed tomographic scans at 120 hours.ConclusionsRemodeling of the spinal cord blood supply—including dilatation of the ASA and proliferation of small collateral vessels—is evident at 48 and 120 hours after extensive SA sacrifice. It is likely that exploitation of this process will prove valuable in the quest to eliminate paraplegia after TAA aneurysm repair
FK228 Analogues Induce Fetal Hemoglobin in Human Erythroid Progenitors
Fetal hemoglobin (HbF) improves the clinical severity of sickle cell disease (SCD), therefore, research to identify HbF-inducing agents for treatment purposes is desirable. The focus of our study is to investigate the ability of FK228 analogues to induce HbF using a novel KU812 dual-luciferase reporter system. Molecular modeling studies showed that the structure of twenty FK228 analogues with isosteric substitutions did not disturb the global structure of the molecule. Using the dual-luciferase system, a subgroup of FK228 analogues was shown to be inducers of HbF at nanomolar concentrations. To determine the physiological relevance of these compounds, studies in primary erythroid progenitors confirmed that JMA26 and JMA33 activated HbF synthesis at levels comparable to FK228 with low cellular toxicity. These data support our lead compounds as potential therapeutic agents for further development in the treatment of SCD
A parametrization of the growth index of matter perturbations in various Dark Energy models and observational prospects using a Euclid-like survey
We provide exact solutions to the cosmological matter perturbation equation
in a homogeneous FLRW universe with a vacuum energy that can be parametrized by
a constant equation of state parameter and a very accurate approximation
for the Ansatz . We compute the growth index \gamma=\log
f(a)/\log\Om_m(a), and its redshift dependence, using the exact and
approximate solutions in terms of Legendre polynomials and show that it can be
parametrized as in most cases. We then
compare four different types of dark energy (DE) models: CDM, DGP,
and a LTB-large-void model, which have very different behaviors at
z\gsim1. This allows us to study the possibility to differentiate between
different DE alternatives using wide and deep surveys like Euclid, which will
measure both photometric and spectroscopic redshifts for several hundreds of
millions of galaxies up to redshift . We do a Fisher matrix analysis
for the prospects of differentiating among the different DE models in terms of
the growth index, taken as a given function of redshift or with a principal
component analysis, with a value for each redshift bin for a Euclid-like
survey. We use as observables the complete and marginalized power spectrum of
galaxies and the Weak Lensing (WL) power spectrum. We find that, using
, one can reach (2%, 5%) errors in , and (4%, 12%) errors in
, while using WL we get errors at least twice as large.
These estimates allow us to differentiate easily between DGP, models and
CDM, while it would be more difficult to distinguish the latter from a
variable equation of state parameter or LTB models using only the growth
index.}Comment: 29 pages, 7 figures, 6 table
Monte Carlo simulation of virtual Compton scattering below pion threshold
This paper describes the Monte Carlo simulation developed specifically for
the VCS experiments below pion threshold that have been performed at MAMI and
JLab. This simulation generates events according to the (Bethe-Heitler + Born)
cross section behaviour and takes into account all relevant
resolution-deteriorating effects. It determines the `effective' solid angle for
the various experimental settings which are used for the precise determination
of photon electroproduction absolute cross section.Comment: 24 pages, 6 figures, to be published in Nuclear Instruments and
Methods in Physics Research, A One author adde
Spatially valid proprioceptive cues improve the detection of a visual stimulus
Vision and proprioception are the main sensory modalities that convey hand location and direction of movement. Fusion of these sensory signals into a single robust percept is now well documented. However, it is not known whether these modalities also interact in the spatial allocation of attention, which has been demonstrated for other modality pairings. The aim of this study was to test whether proprioceptive signals can spatially cue a visual target to improve its detection. Participants were instructed to use a planar manipulandum in a forward reaching action and determine during this movement whether a near-threshold visual target appeared at either of two lateral positions. The target presentation was followed by a masking stimulus, which made its possible location unambiguous, but not its presence. Proprioceptive cues were given by applying a brief lateral force to the participant’s arm, either in the same direction (validly cued) or in the opposite direction (invalidly cued) to the on-screen location of the mask. The d′ detection rate of the target increased when the direction of proprioceptive stimulus was compatible with the location of the visual target compared to when it was incompatible. These results suggest that proprioception influences the allocation of attention in visual spac
A mass-dependent density profile for dark matter haloes including the influence of galaxy formation
We introduce a mass-dependent density profile to describe the distribution of dark matter within galaxies, which takes into account the stellar-to-halo mass dependence of the response of dark matter to baryonic processes. The study is based on the analysis of hydrodynamically simulated galaxies from dwarf to Milky Way mass, drawn from the Making Galaxies In a Cosmological Context project, which have been shown to match a wide range of disc scaling relationships. We find that the best-fitting parameters of a generic double power-law density profile vary in a systematic manner that depends on the stellar-to-halo mass ratio of each galaxy. Thus, the quantity M⋆/Mhalo constrains the inner (γ) and outer (β) slopes of dark matter density, and the sharpness of transition between the slopes (α), reducing the number of free parameters of the model to two. Due to the tight relation between stellar mass and halo mass, either of these quantities is sufficient to describe the dark matter halo profile including the effects of baryons. The concentration of the haloes in the hydrodynamical simulations is consistent with N-body expectations up to Milky Way-mass galaxies, at which mass the haloes become twice as concentrated as compared with pure dark matter runs. This mass-dependent density profile can be directly applied to rotation curve data of observed galaxies and to semi-analytic galaxy formation models as a significant improvement over the commonly used NFW profile
Crossover from 2D ferromagnetic insulator to wide bandgap quantum anomalous Hall insulator in ultra-thin MnBi2Te4
Intrinsic magnetic topological insulators offer low disorder and large
magnetic bandgaps for robust magnetic topological phases operating at higher
temperatures. By controlling the layer thickness, emergent phenomena such as
the Quantum Anomalous Hall (QAH) effect and axion insulator phases have been
realised. These observations occur at temperatures significantly lower than the
Neel temperature of bulk MnBi2Te4, and measurement of the magnetic energy gap
at the Dirac point in ultra-thin MnBi2Te4 has yet to be achieved. Critical to
achieving the promise of this system is a direct measurement of the
layer-dependent energy gap and verifying whether the gap is magnetic in the QAH
phase. Here we utilise temperature dependent angle-resolved photoemission
spectroscopy to study epitaxial ultra-thin MnBi2Te4. We directly observe a
layer dependent crossover from a 2D ferromagnetic insulator with a bandgap
greater than 780 meV in one septuple layer (1 SL) to a QAH insulator with a
large energy gap (>100 meV) at 8 K in 3 and 5 SL MnBi2Te4. The QAH gap is
confirmed to be magnetic in origin, as it abruptly diminishes with increasing
temperature above 8 K. The direct observation of a large magnetic energy gap in
the QAH phase of few-SL MnBi2Te4 is promising for further increasing the
operating temperature of QAH materials
High-precision multi-band measurements of the angular clustering of X-ray sources
In this paper we present the two-point angular correlation function of the
X-ray source population of 1063 XMM-Newton observations at high Galactic
latitudes, comprising up to ~30000 sources over a sky area of 125.5 sq. deg, in
three energy bands: 0.5-2 (soft), 2-10 (hard), and 4.5-10 (ultrahard) keV. We
have measured the angular clustering of our survey and find significant
positive clustering signals in the soft and hard bands, and a marginal
clustering detection in the ultrahard band. We find dependency of the
clustering strength on the flux limit and no significant differences in the
clustering properties between sources with high hardness ratios and those with
low hardness ratios. Our results show that obscured and unobscured objects
share similar clustering properties and therefore they both reside in similar
environments, in agreement with the unified model of AGN. We deprojected the
angular clustering parameters via Limber's equation to compute their typical
spatial lengths. From that we have inferred the typical mass of the dark matter
haloes in which AGN at redshifts of ~1 are embedded. The short AGN lifetimes
derived suggest that AGN activity might be a transient phase that can be
experienced several times by a large fraction of galaxies throughout their
lives.Comment: 14 pages, 9 figures, accepted for publication in Astronomy and
Astrophysic
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