Multistep greedy algorithm identifies community structure in real-world and computer-generated networks

We have recently introduced a multistep extension of the greedy algorithm for modularity optimization. The extension is based on the idea that merging l pairs of communities (l>1) at each iteration prevents premature condensation into few large communities. Here, an empirical formula is presented for the choice of the step width l that generates partitions with (close to) optimal modularity for 17 real-world and 1100 computer-generated networks. Furthermore, an in-depth analysis of the communities of two real-world networks (the metabolic network of the bacterium E. coli and the graph of coappearing words in the titles of papers coauthored by Martin Karplus) provides evidence that the partition obtained by the multistep greedy algorithm is superior to the one generated by the original greedy algorithm not only with respect to modularity but also according to objective criteria. In other words, the multistep extension of the greedy algorithm reduces the danger of getting trapped in local optima of modularity and generates more reasonable partitions.Comment: 17 pages, 2 figure

Exact renormalisation group flow for ultracold Fermi gases in unitary limit

We study the exact renormalisation group flow for ultracold Fermi-gases in unitary regime. We introduce a pairing field to describe the formation of the Cooper pairs, and take a simple ansatz for the effective action. Set of approximate flow equations for the effective couplings including boson and fermionic fluctuations is derived. At some value of the running scale, the system undergoes a phase transition to a gapped phase. The values of the energy density, chemical potential, pairing gap and the corresponding proportionality constants relating the interacting and non-interacting Fermi gases are calculated. Standard mean field results are recovered if we omit the boson loops.Comment: 11 pages, Revtex, misprints corrected, references and comments adde

Expansion velocity of a one-dimensional, two-component Fermi gas during the sudden expansion in the ballistic regime

We show that in the sudden expansion of a spin-balanced two-component Fermi gas into an empty optical lattice induced by releasing particles from a trap, over a wide parameter regime, the radius $R_n$ of the particle cloud grows linearly in time. This allow us to define the expansion velocity $V_{ex}$ from $R_n=V_{ex}t$. The goal of this work is to clarify the dependence of the expansion velocity on the initial conditions which we establish from time-dependent density matrix renormalization group simulations, both for a box trap and a harmonic trap. As a prominent result, the presence of a Mott-insulating region leaves clear fingerprints in the expansion velocity. Our predictions can be verified in experiments with ultra-cold atoms.Comment: 8 pages 10 figures, version as published with minor stylistic change

Measuring the Impact of Agglomeration on Productivity: Evidence from Chilean Retailers

This research extends the agglomeration literature to a country that has not been studied and a market sector that has received little attention. The majority of research that examines how density affects productivity has indirectly measured productivity through worker wages or property prices. The research uses individual supermarkets’ store productivity, proxied by 10 years of annual sales per square foot. Studying supermarkets permits the examination of the effect consumers might have on productivity. Agglomerations (density) could increase or decrease productivity depending on the relative extent of increased competition versus productivity gains, as consumers choose where to shop based on their interests in reducing shopping time (transport costs) and comparison shopping (product quality and pricing). Stores are described by who operates the store, the brand of the store and the size of the store. Results indicate that density has a differential impact depending on the store itself and the mix of stores nearby

Progressively excluding mammals of different body size affects community and trait structure of ground beetles

Mammalian grazing induces changes in vegetation properties in grasslands, which can affect a wide variety of other animals including many arthropods. However, the impacts may depend on the type and body size of these mammals. Furthermore, how mammals influence functional trait syndromes of arthropod communities is not well known. We progressively excluded large (e.g. red deer, chamois), medium (e.g. alpine marmot, mountain hare), and small (e.g. mice) mammals using size-selective fences in two vegetation types (short- and tall-grass vegetation) of subalpine grasslands. We then assessed how these exclusions affected the community composition and functional traits of ground beetles (Coleoptera, Carabidae), and which vegetation characteristic mediated the observed effects. Total carabid biomass, the activity densities of carabids with specific traits (i.e. small eyes, short wings), the richness of small-eyed species and the richness of herbivorous species were significantly higher when certain mammals were excluded compared to when all mammals had access, regardless of vegetation type. Excluding large and medium mammals increased the activity density of herbivorous carabid species, but only in short-grass vegetation. Similarly, excluding large mammals (ungulates) altered carabid species composition in the short-, but not in the tall-grass vegetation. All these responses were related to aboveground plant biomass, but not to plant Shannon diversity or vegetation structural heterogeneity. Our results indicate that changes in aboveground plant biomass are key drivers of mammalian grazers' influence on carabids, suggesting that bottom-up forces are important in subalpine grassland systems. The exclusion of ungulates provoked the strongest carabid response. Our results, however, also highlight the ecological significance of smaller herbivorous mammals. Our study furthermore shows that mammalian grazing not only altered carabid community composition, but also caused community-wide functional trait shifts, which could potentially have a wider impact on species interactions and ecosystem functioning

A bibliometric analysis of clinical research on fracture-related infection

Background: Infection following orthopaedic trauma surgery is increasingly recognized as one of the major research priorities with as primary goal, improving patient care. This increased interest has been anecdotally recognized through published research, research grants, and, finally, with the development of the fracture-related infection (FRI) consensus group. In 2017, the accepted consensus definition of FRI was published, which has been followed by consensus recommendations from both a surgical and medical perspective. A bibliometric analysis was performed to objectively describe the trends in published clinical research related to FRI. Methods: The terms related to FRI were searched in the Web of Science database between 2000 and 2020. The characteristics of clinical research on FRI regarding the author, country, journal, institution, scientific output, top 100 most cited articles, and trend topics were analyzed using Bibliometrix and WPS Office. Results: A total of 2597 records were eligible for inclusion in this bibliometric approach, with studies originating from 89 countries, including eight languages. The United States of America (USA) published the highest number of articles and citations. International collaborations were present between 72 countries, with the most active country being the USA. The most contributive institution was the University of California. The highest number of papers and citations were from the Injury-International Journal of the Care of the Injured and the Journal of Orthopaedic Trauma. The top 100 most cited articles were published in 27 different journals, with the number of citations ranging between 97 and 1004. The latest trend topics were related to the diagnosis of FRI. Conclusion: The present bibliometric analysis shows the research characteristics and trends of FRI from multiple perspectives. The fact that there is an increasing number of studies being published on FRI shows the agreement among scientists and clinicians that standardization with respect to this topic is very important

Diffusion algebras

We define the notion of "diffusion algebras". They are quadratic Poincare-Birkhoff-Witt (PBW) algebras which are useful in order to find exact expressions for the probability distributions of stationary states appearing in one-dimensional stochastic processes with exclusion. One considers processes in which one has N species, the number of particles of each species being conserved. All diffusion algebras are obtained. The known examples already used in applications are special cases in our classification. To help the reader interested in physical problems, the cases N=3 and 4 are listed separately.Comment: 29 pages; minor misprints corrected, few references adde

Toponyms for centers of endemism in Madagascar

A biogeographical model was proposed in 2006 to explain the centers of endemism and the importance of riparian forest of some watersheds as refuges or dispersal corridors during paleoclimatic oscillations. Here, we consider these geographical features highlighting their biological and socio-cultural importance. We explain the etymology or eponymy of the major rivers of the retreat - dispersal watersheds, i.e., the drainage basins of Bemarivo, Antainambalana, Mangoro, Manampatrana, Mananara South, Mandrare, Onilahy, Mangoky, Tsiribihina, Betsiboka, Maevarano, Sambirano, and Mahavavy North. We propose a toponymy for each of the 15 centers of endemism and highlight their peculiarities. We named the centers of endemism of Vohimarina, Masoala, Analanjirofo, Tanala, Manombo, Anosy, Ranopiso, Karimbola, Mikea, Menabe, Melaky, Sofia, Ampasindava, Ankify, and Ankarana. We illustrate each center of endemism with a flagship species and report on its natural and cultural histories, and conservation.RÉSUMÉUn modèle biogéographique a été proposé en 2006 pour expliquer les centres d’endémisme de la biodiversité et l’importance des ripisylves de certains bassins versants en tant que refuges ou couloirs de dispersion au cours des oscillations paléoclimatiques. Ici, nous considérons ces dispositifs géographiques en soulignant leur importance biologique et socio-culturelle. Dans un premier temps, nous expliquons la toponymie ou l’éponymie des grands fleuves des bassins refuges et de dispersion, à savoir les bassins de la Bemarivo, de l’Antainambalana, du Mangoro, de la Manampatrana, de la Mananara du Sud, du Mandrare, de l’Onilahy, du Mangoky, de la Tsiribihina, de la Betsiboka, de la Maevarano, du Sambirano et de la Mahavavy du Nord. Puis nous proposons une toponymie pour chacun des 17 centres et sous-centres d’endémisme en justifiant leurs particularités. Nous retenons ainsi les centres d’endémisme de Vohimarina, de l’Atsinanana (dont Masoala et Analanjirofo), Tanala, de Manombo, de l’Anosy, d’Ala maika (dont Ranopiso, Karimbola et Mikea), du Menabe, du Melaky, de la Sofia, d’Ampasindava, d’Ankify et de l’Ankarana. Nous illustrons chacun des centres d’endémisme avec une espèce symbolique et rapportons des aspects de son histoire naturelle et culturelle ainsi que de sa conservation