Does Our World “weigh” Less Right Now? The Gravitational Pull in a Scientific Collaboration Network is Getting Weaker with Time

We study the geographical patterns of scientific collaboration from a large sample of research papers and letters written by two authors that appeared in the magazine Nature over two sub-periods, before and after the popularization of Internet use. We report three results: First, the distance distribution of co-authors is fat-tailed, in agreement with other studies that find gravitational law in collaboration networks. Second, in the later period the distance distribution dominates the range of commute-distance and beyond (\u3e50km), which renders the city the atomic unit for statistical testing. Last, strong geographical clustering remains a major generative factor in this network. Assuming the universality of this law, we estimate the gravitational constant from the pull between scientists in the network. We find that this constant has decreased two-fold over the last three decades while the other coefficients remain stable. This may indicate that the gravitational constant absorbs changes in the environment that render distances easier to cross, namely a “lighter world

Dissortative From the Outside, Assortative From the Inside: Social Structure and Behavior in the Industrial Trade Network

It is generally accepted that neighboring nodes in financial networks are negatively assorted with respect to the correlation between their degrees. This feature would play an important 'damping' role in the market during downturns (periods of distress) since this connectivity pattern between firms lowers the chances of auto-amplifying (the propagation of) distress. In this paper we explore a trade-network of industrial firms where the nodes are suppliers or buyers, and the links are those invoices that the suppliers send out to their buyers and then go on to present to their bank for discounting. The network was collected by a large Italian bank in 2007, from their intermediation of the sales on credit made by their clients. The network also shows dissortative behavior as seen in other studies on financial networks. However, when looking at the credit rating of the firms, an important attribute internal to each node, we find that firms that trade with one another share overwhelming similarity. We know that much data is missing from our data set. However, we can quantify the amount of missing data using information exposure, a variable that connects social structure and behavior. This variable is a ratio of the sales invoices that a supplier presents to their bank over their total sales. Results reveal a non-trivial and robust relationship between the information exposure and credit rating of a firm, indicating the influence of the neighbors on a firm's rating. This methodology provides a new insight into how to reconstruct a network suffering from incomplete information.Comment: 10 pages, 10 figures, To appear in conference proceedings of the IEEE: HICSS-4

Unusual Spatial Patterns of Industrial Firm Locations Uncover their Social Interactions

In this paper we report evidence from the Italian industrial sectors whereby firms that buy and sell are spatially distributed with a pattern that reflects the microeconomic powers at play. The main finding is that firms are neither clustered around population centers nor are they situated at random. Although geography has an important role in shaping the population map of Italy, the reasons for the positional pattern of buyers and sellers appear to be social. Geographic proximity between sellers and their buyers is supported by the excess in short-distance social ties.

Missing Data as Part of the Social Behavior in Real-World Financial Complex Systems

Many real-world networks are known to exhibit facts that counter our knowledge prescribed by the theories on network creation and communication patterns. A common prerequisite in network analysis is that information on nodes and links will be complete because network topologies are extremely sensitive to missing information of this kind. Therefore, many real-world networks that fail to meet this criterion under random sampling may be discarded. In this paper we offer a framework for interpreting the missing observations in network data under the hypothesis that these observations are not missing at random. We demonstrate the methodology with a case study of a financial trade network, where the awareness of agents to the data collection procedure by a self-interested observer may result in strategic revealing or withholding of information. The non-random missingness has been overlooked despite the possibility of this being an important feature of the processes by which the network is generated. The analysis demonstrates that strategic information withholding may be a valid general phenomenon in complex systems. The evidence is sufficient to support the existence of an influential observer and to offer a compelling dynamic mechanism for the creation of the network.Comment: 17 pages, 12 figure

DNA uracil repair initiated by the archaeal ExoIII homologue Mth212 via direct strand incision

No genes for any of the known uracil DNA glycosylases of the UDG superfamily are present in the genome of Methanothermobacter thermautotrophicus ΔH, making it difficult to imagine how DNA-U repair might be initiated in this organism. Recently, Mth212, the ExoIII homologue of M. thermautotrophicus ΔH has been characterized as a DNA uridine endonuclease, which suggested the possibility of a novel endonucleolytic entry mechanism for DNA uracil repair. With no system of genetic experimentation available, the problem was approached biochemically. Assays of DNA uracil repair in vitro, promoted by crude cellular extracts, provide unequivocal confirmation that this mechanism does indeed operate in M. thermautotrophicus ΔH

Protecting the privacy of individual general practice patient electronic records for geospatial epidemiology research

Background: General practitioner (GP) practices in Australia are increasingly storing patient information in electronic databases. These practice databases can be accessed by clinical audit software to generate reports that inform clinical or population health decision making and public health surveillance. Many audit software applications also have the capacity to generate de-identified patient unit record data. However, the de-identified nature of the extracted data means that these records often lack geographic information. Without spatial references, it is impossible to build maps reflecting the spatial distribution of patients with particular conditions and needs. Links to socioeconomic, demographic, environmental or other geographically based information are also not possible. In some cases, relatively coarse geographies such as postcode are available, but these are of limited use and researchers cannot undertake precision spatial analyses such as calculating travel times. Methods: We describe a method that allows researchers to implement meaningful mapping and spatial epidemiological analyses of practice level patient data while preserving privacy. Results: This solution has been piloted in a diabetes risk research project in the patient population of a practice in Adelaide. Conclusions and Implications: The method offers researchers a powerful means of analysing geographic clinic data in a privacy-protected manner

DNA uracil repair initiated by the archaeal ExoIII homologue Mth212 via direct strand incision

No genes for any of the known uracil DNA glycosylases of the UDG superfamily are present in the genome of Methanothermobacter thermautotrophicus ΔH, making it difficult to imagine how DNA-U repair might be initiated in this organism. Recently, Mth212, the ExoIII homologue of M. thermautotrophicus ΔH has been characterized as a DNA uridine endonuclease, which suggested the possibility of a novel endonucleolytic entry mechanism for DNA uracil repair. With no system of genetic experimentation available, the problem was approached biochemically. Assays of DNA uracil repair in vitro, promoted by crude cellular extracts, provide unequivocal confirmation that this mechanism does indeed operate in M. thermautotrophicus ΔH