Evolution of Cooperation and Coordination in a Dynamically Networked Society

Situations of conflict giving rise to social dilemmas are widespread in society and game theory is one major way in which they can be investigated. Starting from the observation that individuals in society interact through networks of acquaintances, we model the co-evolution of the agents' strategies and of the social network itself using two prototypical games, the Prisoner's Dilemma and the Stag Hunt. Allowing agents to dismiss ties and establish new ones, we find that cooperation and coordination can be achieved through the self-organization of the social network, a result that is non-trivial, especially in the Prisoner's Dilemma case. The evolution and stability of cooperation implies the condensation of agents exploiting particular game strategies into strong and stable clusters which are more densely connected, even in the more difficult case of the Prisoner's Dilemma.Comment: 18 pages, 14 figures. to appea

Mesoscopic structure conditions the emergence of cooperation on social networks

We study the evolutionary Prisoner's Dilemma on two social networks obtained from actual relational data. We find very different cooperation levels on each of them that can not be easily understood in terms of global statistical properties of both networks. We claim that the result can be understood at the mesoscopic scale, by studying the community structure of the networks. We explain the dependence of the cooperation level on the temptation parameter in terms of the internal structure of the communities and their interconnections. We then test our results on community-structured, specifically designed artificial networks, finding perfect agreement with the observations in the real networks. Our results support the conclusion that studies of evolutionary games on model networks and their interpretation in terms of global properties may not be sufficient to study specific, real social systems. In addition, the community perspective may be helpful to interpret the origin and behavior of existing networks as well as to design structures that show resilient cooperative behavior.Comment: Largely improved version, includes an artificial network model that fully confirms the explanation of the results in terms of inter- and intra-community structur

Enhanced error estimator based on a nearly equilibrated moving least squares recovery technique for FEM and XFEM

In this paper a new technique aimed to obtain accurate estimates of the error in energy norm using a moving least squares (MLS) recovery-based procedure is presented. We explore the capabilities of a recovery technique based on an enhanced MLS fitting, which directly provides continuous interpolated fields, to obtain estimates of the error in energy norm as an alternative to the superconvergent patch recovery (SPR). Boundary equilibrium is enforced using a nearest point approach that modifies the MLS functional. Lagrange multipliers are used to impose a nearly exact satisfaction of the internal equilibrium equation. The numerical results show the high accuracy of the proposed error estimator

Early changes in Orthopteran assemblages after grassland restoration : a comparison of space-for-time substitution versus repeated-measures monitoring

Grasslands harbour significant biodiversity and their restoration is a common intervention in biodiversity conservation. However, we know very little on how grassland restoration influences arthropod groups. Here we compared orthopteran assemblages in croplands, natural grasslands and one to four-year-old grasslands restored in a large-scale restoration on former croplands in Hortobágy National Park (E-Hungary). Sampling was done by standardized sweep-netting both in a repeated measures design and space-for-time substitution (chronosequence) design. General linear models with repeated measures from five years showed that species richness, abundance and Shannon diversity of orthopterans decreased in the year following restoration but increased afterwards. By the fourth year, species richness almost doubled and abundance increased almost ten-fold in restored grasslands compared to croplands. Multivariate analyses showed that species composition in the first two years did not progress much but by the third and fourth year there was partial overlap with natural grasslands. Local restoration conditions (last crop, seed mixture) and landscape configuration (proportion of natural grasslands < 1 km away) did not influence the above patterns in either the repeated measures or the chronosequence design, whereas time since restoration affected almost all community variables. Our results suggest that generalist ubiquitous species appeared in restored grasslands first and the more sensitive species colonized the restored fields gradually in later years. The qualitative and quantitative properties of the orthopteran assemblages in restored fields did not yet reach those of natural grasslands, therefore, our study suggests that the full regeneration of the orthopteran assemblages takes more than four years

Multimode fibre:Light-sheet microscopy at the tip of a needle

We also thank the UK Engineering and Physics Sciences Research Council for funding under grant EP/J01771X/1. Finally, we would like to thank EXCELLENT TEAMS (CZ.1.07/2.3.00/30.0005) from European Social Fund and CEITEC - Central European Institute of Technology (CZ.1.05/1.1.00/02.0068) from European Regional Development Fund for support.Light-sheet fluorescence microscopy has emerged as a powerful platform for 3-D volumetric imaging in the life sciences. Here, we introduce an important step towards its use deep inside biological tissue. Our new technique, based on digital holography, enables delivery of the light-sheet through a multimode optical fibre - an optical element with extremely small footprint, yet permitting complex control of light transport processes within. We show that this approach supports some of the most advanced methods in light-sheet microscopy: by taking advantage of the cylindrical symmetry of the fibre, we facilitate the wavefront engineering methods for generation of both Bessel and structured Bessel beam plane illumination. Finally, we assess the quality of imaging on a sample of fluorescent beads fixed in agarose gel and we conclude with a proof-of-principle imaging of a biological sample, namely the regenerating operculum prongs of Spirobranchus lamarcki.Publisher PDFPeer reviewe

A 300-year record of sedimentation in a small tilled catena in Hungary based on δ13C, δ15N, and C/N distribution

Purpose Soil erosion is one of the most serious hazards that endanger sustainable food production. Moreover, it has marked effects on soil organic carbon (SOC) with direct links to global warming. At the same time, soil organic matter (SOM) changes in composition and space could influence these processes. The aim of this study was to predict soil erosion and sedimentation volume and dynamics on a typical hilly cropland area of Hungary due to forest clearance in the early eighteenth century. Materials and methods Horizontal soil samples were taken along two parallel intensively cultivated complex convex-concave slopes from the eroded upper parts at mid-slope positions and from sedimentation in toe-slopes. Samples were measured for SOC, total nitrogen (TN) content, and SOMcompounds (δ13C, δ15N, and photometric indexes). They were compared to the horizons of an in situ non-eroded profile under continuous forest. On the depositional profile cores, soil depth prior to sedimentation was calculated by the determination of sediment thickness. Results and discussion Peaks of SOC in the sedimentation profiles indicated thicker initial profiles, while peaks in C/N ratio and δ13C distribution showed the original surface to be ~ 20 cm lower. Peaks of SOC were presumed to be the results of deposition of SOC-enriched soil from the upper slope transported by selective erosion of finer particles (silts and clays). Therefore, changes in δ13C values due to tillage and delivery would fingerprint the original surface much better under the sedimentation scenario than SOC content. Distribution of δ13C also suggests that the main sedimentation phase occurred immediately after forest clearance and before the start of intense cultivation with maize. Conclusions This highlights the role of relief in sheet erosion intensity compared to intensive cultivation. Patterns of δ13C indicate the original soil surface, even in profiles deposited as sediment centuries ago. The δ13C and C/N decrease in buried in situ profiles had the same tendency as recent forest soil, indicating constant SOM quality distribution after burial. Accordingly, microbiological activity, root uptake, and metabolism have not been effective enough to modify initial soil properties

Efficient recovery-based error estimation for the smoothed finite element method for smooth and singular linear elasticity

[EN] An error control technique aimed to assess the quality of smoothed finite element approximations is presented in this paper. Finite element techniques based on strain smoothing appeared in 2007 were shown to provide significant advantages compared to conventional finite element approximations. In particular, a widely cited strength of such methods is improved accuracy for the same computational cost. Yet, few attempts have been made to directly assess the quality of the results obtained during the simulation by evaluating an estimate of the discretization error. Here we propose a recovery type error estimator based on an enhanced recovery technique. The salient features of the recovery are: enforcement of local equilibrium and, for singular problems a ¿smooth + singular¿ decomposition of the recovered stress. We evaluate the proposed estimator on a number of test cases from linear elastic structural mechanics and obtain efficient error estimations whose effectivities, both at local and global levels, are improved compared to recovery procedures not implementing these features.Stephane Bordas would like to thank the partial financial support of the Royal Academy of Engineering and of the Leverhulme Trust for his Senior Research Fellowship Towards the next generation surgical simulators as well as the financial support for Octavio A. Gonzalez-Estrada and Stephane Bordas from the UK Engineering Physical Science Research Council (EPSRC) under grant EP/G042705/1 Increased Reliability for Industrially Relevant Automatic Crack Growth Simulation with the eXtended Finite Element Method. Stephane Bordas also thanks partial financial support of the European Research Council Starting Independent Research Grant (ERC Stg grant agreement No. 279578) and the FP7 Initial Training Network Funding under grant number 289361 "Integrating Numerical Simulation and Geometric Design Technology, INSIST". This work has been carried out within the framework of the research project DPI2010-20542 of the Ministerio de Ciencia e Innovacion (Spain). The financial support from Universitat Politecnica de Valencia, PROMETEO/2012/023 and Generalitat Valenciana are also acknowledged.González Estrada, OA.; Natarajan, S.; J.J. Ródenas; Nguyen-Xuan, H.; Bordas, S. (2013). Efficient recovery-based error estimation for the smoothed finite element method for smooth and singular linear elasticity. Computational Mechanics. 52(1):37-52. https://doi.org/10.1007/s00466-012-0795-6S3752521Liu GR, Dai KY, Nguyen TT (2006) A smoothed finite element method for mechanics problems. Comput Mech 39(6): 859–877. doi: 10.1007/s00466-006-0075-4Liu GR, Nguyen TT, Dai KY, Lam KY (2007) Theoretical aspects of the smoothed finite element method (SFEM). Int J Numer Methods Eng 71(8): 902–930Nguyen-Xuan H, Bordas SPA, Nguyen-Dang H (2008) Smooth finite element methods: convergence, accuracy and properties. Int J Numer Methods Eng 74(2): 175–208. doi: 10.1002/nmeBordas SPA, Natarajan S (2010) On the approximation in the smoothed finite element method (SFEM). Int J Numer Methods Eng 81(5): 660–670. doi: 10.1002/nmeZhang HH, Liu SJ, Li LX (2008) On the smoothed finite element method. Int J Numer Methods Eng 76(8): 1285–1295. doi: 10.1002/nme.2460Nguyen-Thoi T, Liu G, Lam K, Zhang G. (2009) A face-based smoothed finite element method (FS-FEM) for 3D linear and nonlinear solid mechanics using 4-node tetrahedral elements. Int J Numer Methods Eng 78: 324–353Liu G, Nguyen-Thoi T, Lam K (2009) An edge-based smoothed finite element method (ES-FEM) for static, free and forced vibration analyses of solids. J Sound Vib 320: 1100–1130Liu G, Nguyen-Thoi T, Nguyen-Xuan H, Lam K (2009) A node based smoothed finite element method (NS-FEM) for upper bound solution to solid mechanics problems. Comput Struct 87: 14–26Liu G. Smoothed Finite Element Methods. CRC Press, 2010Liu G, Nguyen-Xuan H, Nguyen-Thoi T (2010) A theoretical study on the smoothed FEM (SFEM) models: Properties, accuracy and convergence rates. Int J Numer Methods Biomed Eng 84: 1222–1256Nguyen T, Liu G, Dai K, Lam K (2007) smoothed finite element method. Tsinghua Sci Technol 12: 497–508Hung NX, Bordas S, Hung N (2009) Addressing volumetric locking and instabilities by selective integration in smoothed finite element. Commun Numer Methods Eng 25: 19–34Nguyen-Xuan H, Rabczuk T, Bordas S, Debongnie JF (2008) A smoothed finite element method for plate analysis. Comput Methods Appl Mech Eng 197: 1184–1203Nguyen NT, Rabczuk T, Nguyen-Xuan H, Bordas S (2008) A smoothed finite element method for shell analysis. Comput Methods Appl Mech Eng 198: 165–177Bordas SPA, Rabczuk T, Hung NX, Nguyen VP, Natarajan S, Bog T, óuan DM, Hiep NV (2010) Strain smoothing in FEM and XFEM. Comput Struct 88(23–24): 1419–1443. doi: 10.1016/j.compstruc.2008.07.006Bordas SP, Natarajan S, Kerfriden P, Augarde CE, Mahapatra DR, Rabczuk T, Pont SD (2011) On the performance of strain smoothing for óuadratic and enriched finite element approximations (XFEM/GFEM/PUFEM). Int J Numer Methods Biomed Eng 86: 637–666Liu G, Nguyen-Thoi T, Nguyen-Xuan H, Dai K, Lam K (2009) On the essence and the evaluation of the shape functions for the smoothed finite element method (SFEM). Int J Numer Methods Eng 77: 1863–1869. doi: 10.1002/nme.2587Strouboulis T, Zhang L, Wang D, Babuška I. (2006) A posteriori error estimation for generalized finite element methods. Comput Methods Appl Mech Eng 195(9–12): 852–879Bordas SPA, Duflot M (2007) Derivative recovery and a posteriori error estimate for extended finite elements. Comput Methods Appl Mech Eng 196(35–36): 3381–3399Xiao óZ, Karihaloo BL (2004) Statically admissible stress recovery using the moving least sóuares technique. In: Topping BHV, Soares CAM (eds) Progress in computational structures technology. Saxe-Coburg Publications, Stirling, pp 111–138Ródenas JJ, González-Estrada OA, Tarancón JE, Fuenmayor FJ (2008) A recovery-type error estimator for the extended finite element method based on singular + smooth stress field splitting. Int J Numer Methods Eng 76(4): 545–571. doi: 10.1002/nme.2313Panetier J, Ladevèze P, Chamoin L (2010) Strict and effective bounds in goal-oriented error estimation applied to fracture mechanics problems solved with XFEM. Int J Numer Methods Eng 81(6): 671–700Barros FB, Proenca SPB, de Barcellos CS (2004) On error estimator and p-adaptivity in the generalized finite element method. Int J Numer Methods Eng 60(14):2373–2398. doi: 10.1002/nme.1048Nguyen-Thoi T, Liu G, Nguyen-Xuan H, Nguyen-Tran C (2011) Adaptive analysis using the node-based smoothed finite element method (NS-FEM). Int J Numer Methods Biomed Eng 27(2): 198–218. doi: 10.1002/cnmGonzález-Estrada OA, Ródenas JJ, Bordas SPA, Duflot M, Kerfriden P, Giner E (2012) On the role of enrichment and statical admissibility of recovered fields in a-posteriori error estimation for enriched finite element methods. Eng Comput 29(8)Zienkiewicz OC, Zhu JZ (1987) A simple error estimator and adaptive procedure for practical engineering analysis. Int J Numer Methods Eng 24(2): 337–357Ródenas JJ, González-Estrada OA, Díez P, Fuenmayor FJ (2010) Accurate recovery-based upper error bounds for the extended finite element framework. Comput Methods Appl Mech Eng 199(37–40): 2607–2621Williams ML (1952) Stress singularities resulting from various boundary conditions in angular corners of plate in extension. J Appl Mech 19: 526–534Szabó BA, Babuška I (1991) Finite element analysis. Wiley, New YorkBarber JR. (2010) Elasticity. Series: solid mechanics and its application, 3rd edn. Springer, DordrechtChen JS, Wu CT, Yoon S, You Y (2001) A stabilized conforming nodal integration for Galerki mesh-free methods. Int J Numer Methods Eng 50: 435–466Yoo J, Moran B, Chen J (2004) Stabilized conforming nodal integration in the natural element method. Int J Numer Methods Eng 60: 861–890Zienkiewicz OC, Zhu JZ (1992) The superconvergent patch recovery and a posteriori error estimates. Part 1: The recovery technique. Int J Numer Methods Eng 33(7): 1331–1364Zienkiewicz OC, Zhu JZ (1992) The superconvergent patch recovery and a posteriori error estimates. Part 2: Error estimates and adaptivity. Int J Numer Methods Eng 33(7): 1365–1382Wiberg NE, Abdulwahab F (1993) Patch recovery based on superconvergent derivatives and eóuilibrium. Int J Numer Methods Eng 36(16): 2703–2724. doi: 10.1002/nme.1620361603Blacker T, Belytschko T (1994) Superconvergent patch recovery with eóuilibrium and conjoint interpolant enhancements. Int J Numer Methods Eng 37(3): 517–536Stein E, Ramm E, Rannacher R (2003) Error-controlled adaptive finite elements in solid mechanics. Wiley, ChichesterDuflot M, Bordas SPA (2008) A posteriori error estimation for extended finite elements by an extended global recovery. 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In: Khalili N, Valliappan S, Li ó, Russell A (eds) 9th World congress on computational mechanics (WCCM9). 4th Asian Pacific Congress on computational methods (APCOM2010). Centre for Infrastructure Engineering and SafetyRódenas JJ, González-Estrada OA, Díez P, Fuenmayor FJ (2007) Upper bounds of the error in the extended finite element method by using an eóuilibrated-stress patch recovery technique. In: International conference on adaptive modeling and simulation (ADMOS 2007). International Center for Numerical Methods in Engineering (CIMNE), pp 210–213Menk A, Bordas S (2010) Numerically determined enrichment function for the extended finite element method and applications to bi-material anisotropic fracture and polycrystals. Int J Numer Methods Eng 83: 805–828Menk A, Bordas S (2011) Crack growth calculations in solder joints based on microstructural phenomena with X-FEM. 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Multi-parametric assessment of the anti-angiogenic effects of liposomal glucocorticoids

Inflammation plays a prominent role in tumor growth. Anti-inflammatory drugs have therefore been proposed as anti-cancer therapeutics. In this study, we determined the anti-angiogenic activity of a single dose of liposomal prednisolone phosphate (PLP-L), by monitoring tumor vascular function and viability over a period of one week. C57BL/6 mice were inoculated subcutaneously with B16F10 melanoma cells. Six animals were PLP-L-treated and six served as control. Tumor tissue and vascular function were probed using MRI before and at three timepoints after treatment. DCE-MRI was used to determine Ktrans, ve, time-to-peak, initial slope and the fraction of non-enhancing pixels, complemented with immunohistochemistry. The apparent diffusion coefficient (ADC), T2 and tumor size were assessed with MRI as well. PLP-L treatment resulted in smaller tumors and caused a significant drop in Ktrans 48 h post-treatment, which was maintained until one week after drug administration. However, this effect was not sufficient to significantly distinguish treated from non-treated animals. The therapy did not affect tumor tissue viability but did prevent the ADC decrease observed in the control group. No evidence for PLP-L-induced tumor vessel normalization was found on histology. Treatment with PLP-L altered tumor vascular function. This effect did not fully explain the tumor growth inhibition, suggesting a broader spectrum of PLP-L activities

Cardiac lymphatics in health and disease

The lymphatic vasculature, which accompanies the blood vasculature in most organs, is indispensable in the maintenance of tissue fluid homeostasis, immune cell trafficking, and nutritional lipid uptake and transport, as well as in reverse cholesterol transport. In this Review, we discuss the physiological role of the lymphatic system in the heart in the maintenance of cardiac health and describe alterations in lymphatic structure and function that occur in cardiovascular pathology, including atherosclerosis and myocardial infarction. We also briefly discuss the role that immune cells might have in the regulation of lymphatic growth (lymphangiogenesis) and function. Finally, we provide examples of how the cardiac lymphatics can be targeted therapeutically to restore lymphatic drainage in the heart to limit myocardial oedema and chronic inflammation.Peer reviewe