Ctenosaura palearis

Number of Pages: 3Integrative BiologyGeological Science

The cause of universality in growth fluctuations

Phenomena as diverse as breeding bird populations, the size of U.S. firms, money invested in mutual funds, the GDP of individual countries and the scientific output of universities all show unusual but remarkably similar growth fluctuations. The fluctuations display characteristic features, including double exponential scaling in the body of the distribution and power law scaling of the standard deviation as a function of size. To explain this we propose a remarkably simple additive replication model: At each step each individual is replaced by a new number of individuals drawn from the same replication distribution. If the replication distribution is sufficiently heavy tailed then the growth fluctuations are Levy distributed. We analyze the data from bird populations, firms, and mutual funds and show that our predictions match the data well, in several respects: Our theory results in a much better collapse of the individual distributions onto a single curve and also correctly predicts the scaling of the standard deviation with size. To illustrate how this can emerge from a collective microscopic dynamics we propose a model based on stochastic influence dynamics over a scale-free contact network and show that it produces results similar to those observed. We also extend the model to deal with correlations between individual elements. Our main conclusion is that the universality of growth fluctuations is driven by the additivity of growth processes and the action of the generalized central limit theorem.Comment: 18 pages, 4 figures, Supporting information provided with the source files

Professional status and norm violation in email collaboration

Purpose Status is a central aspect of teamwork relationships and successful collaboration in teams, both online and offline. Status group membership and status perception shape behavioural expectations and norm perceptions of what is appropriate, but despite their importance have been neglected in previous research. Status effects are of special interest in online collaboration, e.g. via email, where no immediate feedback or non-verbal/paraverbal communication and direct observation is possible. The purpose of this study is to address this gap in research. Design/methodology/approach An experimental scenario study with two different professional status groups (lecturers and students) tested status effects on causal attributions, intergroup bias and emotional and collaborative responses to perceived norm violations in emails. Findings Results overall showed three key findings: a “black-sheep-effect” with harsher negative attributions for same status members, more aggression and less cooperation towards lower status senders and stronger (negative) emotional reactions towards high status senders. Originality/value The findings are important for managing professional online communication because negative personal attributions, strong emotions and aggressive behaviours can increase team conflict, lead to mistakes and generally undermine performance

Nonuniversal power law scaling in the probability distribution of scientific citations

We develop a model for the distribution of scientific citations. The model involves a dual mechanism: in the direct mechanism, the author of a new paper finds an old paper A and cites it. In the indirect mechanism, the author of a new paper finds an old paper A only via the reference list of a newer intermediary paper B, which has previously cited A. By comparison to citation databases, we find that papers having few citations are cited mainly by the direct mechanism. Papers already having many citations ('classics') are cited mainly by the indirect mechanism. The indirect mechanism gives a power-law tail. The 'tipping point' at which a paper becomes a classic is about 21 citations for papers published in the Institute for Scientific Information (ISI) Web of Science database in 1981, 29 for Physical Review D papers published from 1975-1994, and 39 for all publications from a list of high h-index chemists assembled in 2007. The power-law exponent is not universal. Individuals who are highly cited have a systematically smaller exponent than individuals who are less cited.Comment: 7 pages, 3 figures, 2 table

Flight service evaluation of an advanced composite empennage component on commercial transport aircraft. Phase 1: Engineering development

The empennage component selected for this program is the vertical fin box of the L-1011 aircraft. The box structure extends from the fuselage production joint to the tip rib and includes the front and rear spars. Various design options were evaluated to arrive at a configuration which would offer the highest potential for satisfying program objectives. The preferred configuration selected consists of a hat-stiffened cover with molded integrally stiffened spars, aluminum trussed composite ribs, and composite miniwich web ribs with integrally molded caps. Material screening tests were performed to select an advanced composite material system for the Advanced Composite Vertical Fin (ACFV) that would meet the program requirements from the standpoint of quality, reproducibility, and cost. Preliminary weight and cost analysis were made, targets established, and tracking plans developed. These include FAA certification, ancillary test program, quality control, and structural integrity control plans

Changing How We Discount to Make Public Policy More Responsive To Citizens'Time Preferences

Laws and regulations have both benefits and costs, comparisons of which provide useful information. When such benefits and costs occur over time it is normal practice to discount them, with costs in the distant future considered less important than those occurring in the present, and distant benefits less valuable than present benefits. Conventionally, this discounting is done at a constant rate each period'so-called exponential discounting' with both cost and benefit streams being treated as if they were financial assets. However, humans are not exponential discounters. Rather, people tend to discount more than exponentially in the short run but less than exponentially in the long run. Such 'hyperbolic' discounting is empirically ubiquitous but neglected administratively. The recent "data quality act" requires that information utilized by Federal agencies "adhere to a basic standard of quality, including objectivity, utility and integrity." Here we argue that exponential discounting of many benefit streams, particularly non-pecuniary ones, fails the "data quality" test and should be abandoned in favor of empirically-observed hyperbolic discounting.

Increase in Pile Capacity with Time in Missouri River Alluvium

The data measured in this study suggest that the increase in compressive pile capacity for a 42-ft long, HP14x102 pile, in a predominantly fine-grained Missouri River alluvium soil profile, increases by about 16 percent from days seven to forty-four after driving. It appears evident that Davisson’s (1973) failure criteria seems to agree fairly well with the observed plunging failure of two compressive pile-load failure tests performed in Missouri River alluvium. By comparison of compressive proof and failure tests performed on day forty-four after driving, it appears that loading a pile to some degree prior to failure, and then reloading the pile, has almost no affect on the load-settlement relationship. Hence, proof loaded piles in Missouri River alluvium that pass should be allowed for use beneath the structure. Finally, comparisons of tension and compression pile load test data have lead to two possible conclusions. First, the estimation of tip load by tell-tale data may not be accurate, and may underestimate the amount of load actually transferred to the tip. And second, it seems viable that, at this site, the skin friction that can be counted on in design is perhaps 55 to 60 percent of that calculated for compression

Vive la différence: biogenesis and evolution of microRNAs in plants and animals

MicroRNAs are pervasive in both plants and animals, but many aspects of their biogenesis, function and evolution differ. We reveal how these differences contribute to characteristic features of microRNA evolution in the two kingdoms

A Two-Hit Trigger for siRNA Biogenesis in Plants

SummaryIn Arabidopsis, microRNA-directed cleavage can define one end of RNAs that then generate phased siRNAs. However, most miRNA-targeted RNAs do not spawn siRNAs, suggesting the existence of additional determinants within those that do. We find that in moss, phased siRNAs arise from regions flanked by dual miR390 cleavage sites. AtTAS3, an siRNA locus important for development and conserved among higher plants, also has dual miR390 complementary sites. Both sites bind miR390 in vitro and are functionally required in Arabidopsis, but cleavage is undetectable at the 5′ site—demonstrating that noncleavable sites can be functional in plants. Phased siRNAs also emanate from the bounded regions of every Arabidopsis gene with two known microRNA/siRNA complementary sites, but only rarely from genes with single sites. Therefore, two “hits,”—often, but not always, two cleavage events—constitute a conserved trigger for siRNA biogenesis, a finding with implications for recognition and silencing of aberrant RNA