1,691 research outputs found
Social network markets: the influence of network structure when consumers face decisions over many similar choices
In social network markets, the act of consumer choice in these industries is
governed not just by the set of incentives described by conventional consumer
demand theory, but by the choices of others in which an individual's payoff is
an explicit function of the actions of others. We observe two key empirical
features of outcomes in social networked markets. First, a highly right-skewed,
non-Gaussian distribution of the number of times competing alternatives are
selected at a point in time. Second, there is turnover in the rankings of
popularity over time. We show here that such outcomes can arise either when
there is no alternative which exhibits inherent superiority in its attributes,
or when agents find it very difficult to discern any differences in quality
amongst the alternatives which are available so that it is as if no superiority
exists. These features appear to obtain, as a reasonable approximation, in many
social network markets. We examine the impact of network structure on both the
rank-size distribution of choices at a point in time, and on the life spans of
the most popular choices. We show that a key influence on outcomes is the
extent to which the network follows a hierarchical structure. It is the social
network properties of the markets, the meso-level structure, which determine
outcomes rather than the objective attributes of the products.Comment: 14 pages, 5 figure
Sensitivity of the r-process to nuclear masses
The rapid neutron capture process (r-process) is thought to be responsible
for the creation of more than half of all elements beyond iron. The scientific
challenges to understanding the origin of the heavy elements beyond iron lie in
both the uncertainties associated with astrophysical conditions that are needed
to allow an r-process to occur and a vast lack of knowledge about the
properties of nuclei far from stability. There is great global competition to
access and measure the most exotic nuclei that existing facilities can reach,
while simultaneously building new, more powerful accelerators to make even more
exotic nuclei. This work is an attempt to determine the most crucial nuclear
masses to measure using an r-process simulation code and several mass models
(FRDM, Duflo-Zuker, and HFB-21). The most important nuclear masses to measure
are determined by the changes in the resulting r-process abundances. Nuclei
around the closed shells near N=50, 82, and 126 have the largest impact on
r-process abundances irrespective of the mass models used.Comment: 5 pages, 4 figures, accepted in European Physical Journal
Modelling creative innovation
The economic concept of rationality seems inappropriate in the context of creative innovation, because of its assumption that the tastes and preferences of agents are fixed. The concept of copying, of imitating the behaviour of others, has equal claim to the description 'rational' in an innovative context. Models of ‘binary choices with externalities’ are predicated on copying and potentially show us not only why most innovations fail, but also why big social changes do not necessarily require big causes. In the ‘Long-tail’ world of a huge range of choice, however, many choices are not ‘binary, either-or’. In the long-tail world, popular choices tend to become more popular, but not forever, as innovation drives a constant turnover in the popularity rankings. A very simple model of ‘neutral’ copying with occasional originality of choice can explain real-world patterns of long-tail distributions under continual turnover
Ovalbumin sensitization and challenge increases the number of lung cells possessing a mesenchymal stromal cell phenotype
Abstract Background Recent studies have indicated the presence of multipotent mesenchymal stromal cells (MSCs) in human lung diseases. Excess airway smooth muscle, myofibroblasts and activated fibroblasts have each been noted in asthma, suggesting that mesenchymal progenitor cells play a role in asthma pathogenesis. We therefore sought to determine whether MSCs are present in the lungs of ovalbumin (OVA)-sensitized and challenged mice, a model of allergic airways disease. Methods Balb/c mice were sensitized and challenged with PBS or OVA over a 25 day period. Flow cytometry as well as colony forming and differentiation potential were used to analyze the emergence of MSCs along with gene expression studies using immunochemical analyses, quantitative polymerase chain reaction (qPCR), and gene expression beadchips. Results A CD45-negative subset of cells expressed Stro-1, Sca-1, CD73 and CD105. Selection for these markers and negative selection against CD45 yielded a population of cells capable of adipogenic, osteogenic and chondrogenic differentiation. Lungs from OVA-treated mice demonstrated a greater average colony forming unit-fibroblast (CFU-F) than control mice. Sorted cells differed from unsorted lung adherent cells, exhibiting a pattern of gene expression nearly identical to bone marrow-derived sorted cells. Finally, cells isolated from the bronchoalveolar lavage of a human asthma patient showed identical patterns of cell surface markers and differentiation potential. Conclusions In summary, allergen sensitization and challenge is accompanied by an increase of MSCs resident in the lungs that may regulate inflammatory and fibrotic responses.http://deepblue.lib.umich.edu/bitstream/2027.42/78265/1/1465-9921-11-127.xmlhttp://deepblue.lib.umich.edu/bitstream/2027.42/78265/2/1465-9921-11-127.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/78265/3/1465-9921-11-127-S1.DOCPeer Reviewe
Recommended from our members
A Rare Presentation of Orthostatic Tremor as Abdominal Tremor
Background: Orthostatic tremor (OT) is a weight-bearing hyperkinetic disorder characterized by unsteadiness while standing that is relieved when sitting or walking.
Case report: A 66-year-old male presented with a 5 year-history of tremor in his abdomen, but only when he stood in a stationary position. The tremor disappeared when he stood or walked. On examination, he had palpable tremor in his rectus abdominis and gastrocnemius virtually instantaneously after standing. His electromyography findings confirmed the presence of a 12-Hz tremor in the tibialis anterior while standing, with subharmonics recorded in the external obliques and rectus abdominis.
Discussion: Our case illustrates an unusual presentation of OT. The diagnosis is supported by its characteristic frequency and specific appearance only during upright stance
- …