10,070 research outputs found
Who Contributes to the Knowledge Sharing Economy?
Information sharing dynamics of social networks rely on a small set of
influencers to effectively reach a large audience. Our recent results and
observations demonstrate that the shape and identity of this elite, especially
those contributing \emph{original} content, is difficult to predict.
Information acquisition is often cited as an example of a public good. However,
this emerging and powerful theory has yet to provably offer qualitative
insights on how specialization of users into active and passive participants
occurs.
This paper bridges, for the first time, the theory of public goods and the
analysis of diffusion in social media. We introduce a non-linear model of
\emph{perishable} public goods, leveraging new observations about sharing of
media sources. The primary contribution of this work is to show that
\emph{shelf time}, which characterizes the rate at which content get renewed,
is a critical factor in audience participation. Our model proves a fundamental
\emph{dichotomy} in information diffusion: While short-lived content has simple
and predictable diffusion, long-lived content has complex specialization. This
occurs even when all information seekers are \emph{ex ante} identical and could
be a contributing factor to the difficulty of predicting social network
participation and evolution.Comment: 15 pages in ACM Conference on Online Social Networks 201
Special Issue Call for Papers: Mathematics and Society
The Journal of Humanistic Mathematics (http://scholarship.claremont.edu/jhm/) is pleased to announce a call for papers for a special issue on Mathematics and Society. Please send your initial proposal submissions via email to the guest editors by August 15, 2022. Initial submission of complete manuscripts is due December 15, 2022. The issue is currently scheduled to appear in July 2023
catena-Poly[zinc-trisÂ(ÎŒ-dimethylÂcarbamato-Îș2 O:OâČ)-zinc-ÎŒ-(2-phenylÂbenzimidazolido-Îș2 N:NâČ]
The crystal structure of the title compound, [Zn2(C13H9N2)(C3H6NO2)3]n, displays a long chiral chain. This is composed of zinc-dimer clusters capped by dimethylÂcarbamate ligands, which lie on crystallographic twofold rotation axes and are polymerically linked in one dimension by 2-phenylÂbenzimidadole (2âPBImi) organic ligands. The two Zn2+ ions defining the dimetal cluster are crystallographically independent, but display very similar coordination modes and tetraÂhedral geometry. As such, each Zn2+ ion is coordinated on one side by the N-donor imidazole linker, while the other three available coordination sites are fully occupied by the O atoms from the capping dimethylÂcarbamates. The chirality of the chain extends along the c axis, generating a rather long 52.470â
(11)â
Ă
cell axis. InterÂestingly, the chiral material crystallizes from completely achiral precursors. A twofold axis and 31 screw axis serve to generate the long asymmetric unit
VLBI studies of DAGN and SMBHB hosting galaxies
Dual active galactic nuclei (DAGN) and supermassive black hole binaries
(SMBHBs) at kpc and pc-scale separations, respectively, are expected during
stages of galaxy merger and evolution. Their observational identification can
address a range of areas of current astrophysics frontiers including the final
parsec problem and their contribution towards the emission of low-frequency
gravitational waves. This has however been difficult to achieve with current
spectroscopy and time domain strategies. Very long baseline interferometry
(VLBI) as a method of directly imaging radio structures with milli-arcsecond
(mas) and sub-mas resolutions is introduced as a possible means of detecting
DAGN and SMBHBs. We motivate its usage with expected observational signatures
and cite some studies from literature to illustrate its current status, and
present an updated list of candidates imaged with high-resolution radio
observations. We then recall some shortcomings of the method with possible
solutions and discuss future directions, relevant to large surveys with the
upcoming Square Kilometer Array and future space VLBI missions.Comment: 13 pages, 2 table; Radio Science (accepted
MCP-1 overexpressed in tuberous sclerosis lesions acts as a paracrine factor for tumor development
Patients with tuberous sclerosis complex (TSC) develop hamartomatous tumors showing loss of function of the tumor suppressor TSC1 (hamartin) or TSC2 (tuberin) and increased angiogenesis, fibrosis, and abundant mononuclear phagocytes. To identify soluble factors with potential roles in TSC tumorigenesis, we screened TSC skin tumorâderived cells for altered gene and protein expression. Fibroblast-like cells from 10 angiofibromas and five periungual fibromas produced higher levels of monocyte chemoattractant protein-1 (MCP-1) mRNA and protein than did fibroblasts from the same patient's normal skin. Conditioned medium from angiofibroma cells stimulated chemotaxis of a human monocytic cell line to a greater extent than conditioned medium from TSC fibroblasts, an effect blocked by neutralizing MCP-1âspecific antibody. Overexpression of MCP-1 seems to be caused by loss of tuberin function because Eker rat embryonic fibroblasts null for Tsc2 (EEF Tsc2 (â/â)) produced 28 times as much MCP-1 protein as did EEF Tsc2 (+/+) cells; transient expression of WT but not mutant human TSC2 by EEF Tsc2 (â/â) cells inhibited MCP-1 production; and pharmacological inhibition of the Rheb-mTOR pathway, which is hyperactivated after loss of TSC2, decreased MCP-1 production by EEF Tsc2 (â/â) cells. Together these findings suggest that MCP-1 is an important paracrine factor for TSC tumorigenesis and may be a new therapeutic target
Gene expression and functional comparison between multipotential stromal cells from lateral and medial condyles of knee osteoarthritis patients
Osteoarthritis (OA) is the most common degenerative joint disorder. Multipotential stromal cells (MSCs) have a crucial role in joint repair, but how OA severity affects their characteristics remains unknown. Knee OA provides a good model to study this, as osteochondral damage is commonly more severe in the medial weight-bearing compartment compared to lateral side of the joint. This study utilised in vitro functional assays, cell sorting, gene expression and immunohistochemistry to compare MSCs from medial and lateral OA femoral condyles. Despite greater cartilage loss and bone sclerosis in medial condyles, there was no significant differences in MSC numbers, growth rates or surface phenotype. Culture-expanded and freshly-purified medial-condyle MSCs expressed higher levels of several ossification-related genes. Using CD271-staining to identify MSCs, their presence and co-localisation with TRAP-positive chondroclasts was noted in the vascular channels breaching the osteochondral junction in lateral condyles. In medial condyles, MSCs were additionally found in small cavities within the sclerotic plate. These data indicate subchondral MSCs may be involved in OA progression by participating in cartilage destruction, calcification and sclerotic plate formation and that they remain abundant in severe disease. Biological or biomechanical modulation of these MSCs may be a new strategy towards cartilage and bone restoration in knee OA
Coexistence of two dune growth mechanisms in a landscape-scale experiment
In landscape-scale experiments at the edge of the Gobi desert, we show that
various dune types develop simultaneously under natural wind conditions. Using
4 years of high-resolution topographic data, we demonstrate that, depending on
sand availability, the same wind regime can lead to two different dune
orientations, which reflect two independent dune growth mechanisms. As periodic
oblique dunes emerge from a sand bed and develop to 2 meters in height, we
analyze defect dynamics that drive the non-linear phase of pattern coarsening.
Starting from conical sand heaps deposited on gravels, we observe the
transition from dome to barchan and asymmetric barchan shapes. We identify a
minimum size for arm elongation and evaluate the contribution of wind reversals
to its longitudinal alignment. These experimental field observations support
existing theoretical models of dune dynamics boosting confidence in their
applicability for quantitative predictions of dune evolution under various wind
regimes and bed conditions
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