Stable and Efficient Structures for the Content Production and Consumption in Information Communities

Real-world information communities exhibit inherent structures that characterize a system that is stable and efficient for content production and consumption. In this paper, we study such structures through mathematical modelling and analysis. We formulate a generic model of a community in which each member decides how they allocate their time between content production and consumption with the objective of maximizing their individual reward. We define the community system as "stable and efficient" when a Nash equilibrium is reached while the social welfare of the community is maximized. We investigate the conditions for forming a stable and efficient community under two variations of the model representing different internal relational structures of the community. Our analysis results show that the structure with "a small core of celebrity producers" is the optimally stable and efficient for a community. These analysis results provide possible explanations to the sociological observations such as "the Law of the Few" and also provide insights into how to effectively build and maintain the structure of information communities.Comment: 21 page

Metapopulation theory explains Black-stripe Minnow (Pisces: Galaxiidae, Galaxiella nigrostriata) distribution in seasonal wetlands in south-west Western Australia

The objective of this project was to determine if Galaxiella nigrostriata populations could belong to a metapopulation. Metapopulation theory describes how multiple populations with occasional connectivity are a ‘population of populations’. Some populations’ habitats have optimal conditions (source habitats), others experience regular extinctions (sink habitats). Connectivity allows repopulation of extinct or uninhabited habitats. Galaxiella nigrostriata occurred randomly in 11 seasonal wetlands in the Kemerton wetland complex in south-west Western Australia over a 16 year period. The wetlands did not appear to be connected. Around 70% of wetlands on the Swan Coastal Plain in south-west WA have been filled or degraded since European settlement around 180 years ago. Of those, seasonal wetlands are at most risk from degradation. Galaxiella nigrostriata mainly live in seasonal wetlands between Augusta and Albany and in three remnant populations on the Swan Coastal Plain. They are small freshwater fish (length), aestivate in moist wetland sediments when wetlands dry and live for about one year. Seasonal wetlands and G. nigrostriata are threatened by nutrient enrichment, salinity, introduced fish, landscape modification and changes to hydroperiod by groundwater abstraction and declining rainfall. Inundated wetlands that previously contained G. nigrostriata, and wetlands where they had not been recorded, were sampled throughout south-west WA. Fish and crayfish abundance was surveyed and water samples analysed on site and in a laboratory. Physical characteristics of each wetland and surrounding landscape were also recorded. Information about wetlands was analysed to determine if physico-chemical characteristics accounted for G. nigrostriata abundance or distribution between wetlands. Lentocorrals were then established in two Kemerton wetlands prior to inundation. They were sampled following inundation to determine how and where within a wetland G. nigrostriata entered the sediment to aestivate. Aestivation was examined to determine whether any physical features may be lacking which could inhibit population persistence. Galaxiella nigrostriata specimens from each population had morphological measurements and counts taken prior to tissue being removed for genetic analyses. Two mitochondrial DNA markers were used to investigate divergence and connectivity within and between populations and catchments. Most wetlands were small (mean 0.6 ha), had tannin-stained water and 41% vegetation cover. All wetlands exceeded guideline values for Fe and Zn and those near agricultural land exceeded guideline values for TN and TP. However, no physico-chemical water properties or habitat features impeded G. nigrostriata abundance or distribution between wetlands. Additionally, it was thought there may be a commensal relationship between G. nigrostriata and burrowing crayfish, with G. nigrostriata using burrows to enter the sediment. No relationship was found between G. nigrostriata, crayfish or their burrows, indicating an alternative way for them to enter the sediment. Genetic research and examination of wetland positions in the landscape confirmed G. nigrostriata populations (particularly Kemerton) are part of metapopulation. This research showed populations between catchments had not connected for thousands of years but populations in wetland complexes had recent connectivity. Management of wetlands requires investigation and monitoring of nearby wetlands which may be part of a metapopulation, and may affect population longevity of all wetlands

Generalized Q Models for Investment

We extend the Q theory of investment to allow for adjustment costs for labor, under the additional assumption that the firm is a monopolistic competitor in the output market. The issue of nonconstant returns to scale is also discussed. We show that the standard Q model is a special case of a more general model involving testable parameter restrictions. Estimates for the U.S. manufacturing sector suggest that the departure from the assumption of perfect competition and lack of adjustment costs for labor receive empirical support in the data

Environmental degradation and indeterminacy of equilibrium selection

This paper analyzes an intertemporal optimization problem in which agents derive utility from three goods: leisure, a public environmental good and the consumption of a produced good. The global analysis of the dynamic system generated by the optimization problem shows that global indeterminacy may arise: given the initial values of the state variables, the economy may converge to different steady states, by choosing different initial values of the control variable

IMPORTING JOBS AND EXPORTING FIRMS? ON THE WAGE AND EMPLOYMENT IMPLICATIONS OF ITALY’S TRADE AND FOREIGN DIRECT INVESTMENT FLOWS

International economic integration is often blamed for the deteriorating fortunes of unskilled workers in industrial countries. We look at the labor market impact of trade and foreign direct investment in the case of Italy. Our empirical framework allows for trade, technology and factor supply effects. We find that international trade did not contribute to Italy’s labor market problems. Indeed, given that Italy holds quite a distinct pattern of trade specialization, compared to other industrialized countries, international integration as reflected in falling import prices may have boosted the demand for labor there. We also argue that the inability of the Mezzogiorno’s economy to adjust to the changing international environment is one of the main stumbling blocks in Italy’s economy. Finally, we find that greater firm’s mobility may have weakened the power of trade unions and contributed to wage moderation.international trade, foreign direct investment,wages, employment

Climate change and migration: Is agriculture the main channel?

Migration and climate change are two of the most important challenges the world currently faces. They are connected as climate change may stimulate or hinder migration. One of the sectors strongly affected by climate change is agriculture, which is the source of income for most of the world's poor. Climate change may affect agricultural productivity and hence migration because of its impact on average temperatures and rainfall and because it increases the frequency and intensity of weather shocks. In this paper we use data on 108 countries from 1960 to 2010 to analyze the relationship between weather variations, changes in agricultural productivity and international migration. We find that negative shocks to agricultural productivity caused by climate fluctuations significantly increase emigration from developing countries, an especially strong impact in poor countries but less so in middle income countries. These results are robust to the definitions of the poor country sample, and to several checks and alternative explanations suggested by the literature. Importantly, our results point to a causal interpretation of the agricultural channel to explain the climate change-migration nexus

Measuring environmental policy stringency: Approaches, validity, and impact on environmental innovation and energy efficiency

Solid tests of the impact of environmental and energy policy on important economic outcomes, such as innovation, productivity, competitiveness and energy and carbon efficiency are impaired by the lack of appropriate empirical proxies for the commitment to, and stringency of, environmental policy. We contribute to the literature by: (1) computing different indicators of environmental policy stringency, (2) testing to what extent they convey similar insights through a statistical comparison exercise, and (3) showing the implications of using one or the other indicator in two illustrative empirical applications focused on environmental innovation and energy efficiency. We conclude by highlighting the implications of our analysis for empirical research focusing on the evaluation of policy impacts, and highlight fruitful future research avenues

Multiparametric Semi-quantitative Scoring System for the histological evaluation of marine fish larval and juvenile quality

Gilthead seabream (GSB - Sparus aurata) and European seabass (ESB - Dicentrarchus labrax) are two of the most farmed fish species in EU. However, production of sea bream/bass in the EU has remained stagnant for the last decade and the Mediterranean EU aquaculture faces significant sustainability challenges. In consideration of this, and as it is largely recognized that the success of marine aquaculture strictly depends on the production of good quality larvae/juveniles, in this paper the authors put forward an original standardized tool for the histological assessment of GSB and ESB larva/juveniles. This tool promptly allows to highlight problems in marine fish larval batches because of managerial practices, suggesting to fish farmers which direction take to resolve them. A Multiparametric Semi-quantitative Scoring System (scoring range 1–5) has been originally developed for larval/juvenile histological evaluation and it includes 18 descriptors related to 6 organ districts. The values of each descriptor can be summarized in two indexes: the CHI (Cumulative Histological Index), giving general information about the quality of a fish batch in that precise moment and the OCV (Organ condition value) showing the general condition of each organ and by the individual descriptors. The paper purposes are to describe the MSSS, the criteria established for the score attribution and to supply some indications for the use of the tool

Market Segmentation Through Information

Prodigious amounts of data are being collected by internet companies about their users' preferences. We consider the information design problem of how to share this information with traditional companies which, in turn, compete on price by offering personalised discounts to customers. We provide a necessary and sufficient condition under which the internet company is able to perfectly segment and monopolise all such markets. This condition is surprisingly mild, and suggests room for regulatory oversight

SDHx mutation and the hereditary Head- and Neck paraganglioma: what the radiologist should know

SDHx mutation is a recent discovery in Head- and Neck-paraganglioma (HNPGLs, once known as "glomus tumors") and genetic fields, showing its influence on imaging workup and therapeutic approach. These pieces of knowledge are increasing over the years along with the emerging clinical value of techniques for genetic analyses