Load-Sharing Policies in Parallel Simulation of Agent-Based Demographic Models

Execution parallelism in agent-Based Simulation (ABS) allows to deal with complex/large-scale models. This raises the need for runtime environments able to fully exploit hardware parallelism, while jointly offering ABS-suited programming abstractions. In this paper, we target last-generation Parallel Discrete Event Simulation (PDES) platforms for multicore systems. We discuss a programming model to support both implicit (in-place access) and explicit (message passing) interactions across concurrent Logical Processes (LPs). We discuss different load-sharing policies combining event rate and implicit/explicit LPs’ interactions. We present a performance study conducted on a synthetic test case, representative of a class of agent-based models

Programming agent-based demographic models with cross-state and message-exchange dependencies: A study with speculative PDES and automatic load-sharing

Agent-based modeling and simulation is a versatile and promising methodology to capture complex interactions among entities and their surrounding environment. A great advantage is its ability to model phenomena at a macro scale by exploiting simpler descriptions at a micro level. It has been proven effective in many fields, and it is rapidly becoming a de-facto standard in the study of population dynamics. In this article we study programmability and performance aspects of the last-generation ROOT-Sim speculative PDES environment for multi/many-core shared-memory architectures. ROOT-Sim transparently offers a programming model where interactions can be based on both explicit message passing and in-place state accesses. We introduce programming guidelines for systematic exploitation of these facilities in agent-based simulations, and we study the effects on performance of an innovative load-sharing policy targeting these types of dependencies. An experimental assessment with synthetic and real-world applications is provided, to assess the validity of our proposal

Public subsidies, TFP and efficiency : a tale of complex relationships

This paper shows that a suitable decomposition of TFP can be applied to a large sample of subsidized firms for a relevant period of time, allowing an evaluation of the impact of subsidies on either the roles of technical progress and technical efficiency change or scale and allocative efficiency change as determinants of granted firms’ long-term growth. We measure and decompose TFP using a Stochastic Frontier Analysis (SFA). The impact of capital subsidies on the different components of TFP is captured by a quasi–experimental method (Multiple RDD), exploiting the conditions for a local random experiment created by Law 488/92 (L488), which has been an important policy instrument for reducing territorial disparities in Italy. The main findings from the case study are twofold. First, capital subsidies positively affect TFP growth in the medium-long term and not in the short term. The main reason is that allocative efficiency has a positive effect only after 2-3 years. Second, the positive impact comes especially through technical progress and not through scale impact change, as may have been expected

Place-based amenities, well-being and territorial competitiveness: a new approach using tourists’ happiness

The well-being generated by each place is an unobservable characteristic affecting local competitiveness and territorial growth. In evaluating local well-being, the use of residents’ perceptions may generate biased evaluations. Alternatively, a revealed-preference analysis of tourists’ happiness might be exploited to assess the quality of life at the destination. Then, we develop a hedonic utility function to analyze a huge and original dataset of foreign tourists’ satisfaction, visiting Italy over 2005-2014, on a large number of place-based amenities. Results show a great diversity in the mix of features that affect tourist well-being at each destination, indicating strong heterogeneity in place-based amenities, correlated in space. The presence of spatially correlated common factors of competitiveness asks for coordinated action plans on the part of local and regional authorities

Ecophysiology of Tilia americana under ozone fumigation

The negative effects of the pollutant gas ozone are widely studied in many plant species, but the intimate mechanisms of toxicity have not been completely defined. Generally this contaminant or its free radical by–products impair membrane functions, leading to declines in physiological processes, accelerated foliar senescence and premature leaf abscission. Trees of the genus Tilia do not show any foliar injury induced by ozone under natural conditions. In this study, we investigated the effects of this pollutant on ecophysiological and biochemical parameters of T. Americana saplings exposed to a fumigation (120 ppb for 45 consecutive days, 5 h d–1). At the end of treatment, even if plants did not exhibit any visible foliar injury, several parameters were significantly affected: stomatal conductance for water vapor (–15% compared to control), net photosynthesis (–39%), intercellular CO2 concentration (+30%), as well as chlorophyll fluorescence indexes. After 45 days of fumigation neo–, viola– and anteraxanthin content significantly decreased (–25%, –34% and –63%, respectively, in comparison with controls), but no zeaxanthin induction was detected, suggesting that exposure did not activate the xanthopyll cycle. Under these circumstances, this species should be regarded as “middle tolerant/sensitive”

Ecophysiological and antioxidant traits of Salvia officinalis under ozone stress

Ecophysiological and antioxidant traits were evaluated in sage (Salvia officinalis) plants exposed to 120 ppb of ozone for 90 consecutive days (5 h day−1). At the end of fumigation, plants showed slight leaf yellowing that could be considered the first visual symptom of leaf senescence. Ozone-stressed leaves showed (1) reduced photosynthetic activity (−70 % at the end of exposure), (2) chlorophyll loss (−59 and −56 % of chlorophyll a and b concentrations, starting from 30 days from the beginning of exposure), and (3) cellular water deficit (−12 % of the relative water content at the end of the fumigation). These phenomena are indicative of oxidative stress in the chloroplasts (as confirmed by the strong degradation of β-carotene) despite the photoprotection conferred by xanthophyll cycle [as demonstrated by the significant rise of de-epoxidation index, reaching the maximum value at the end of the treatment (+69 %)], antioxidant compounds [as confirmed by the increase of phenols (in particular caffeic acid and rosmarinic acid)], and water-soluble carbohydrates (especially monosaccharides). By means of combined ecophysiological and biochemical approaches, this study demonstrates that S. officinalis is able to activate an adaptive survival mechanism allowing the plant to complete its life cycle even under oxidative stressful conditions

Analysis and Optimization of a Demographic Simulator for Parallel Environments

In the past years, the advent of multi-core machines has led to the need for adapting current simulation solutions to modern hardware architectures. In this poster, we present a solution to exploit multicore shared-memory capacities in Yades, a parallel tool for running socio-demography dynamic simulations. We propose to abandon the single-threaded programming approach addresses in Yades by using ROOT-Sim, a library which allows to apply discrete event simulation to parallel environments profiting share-memory capabilities. As a result of this new approach, our results show the improvement in Yades’ performance and scalability

Phenylpropanoids are key players in the antioxidant defense to ozone of European ash, Fraxinus excelsior

Physiological and biochemical responses to ozone (O3) (150 ppb, 8 h day−1, 35 consecutive days) of two Italian provenances (Piedmont and Tuscany) of Fraxinus excelsior L. were evaluated, with special attention to the role of phenylpropanoids. Our results indicate (i) the high O3 sensitivity especially of Piedmont provenance (in terms of visible injury, water status, and photosynthetic apparatus); (ii) although the intra-specific sensitivity to O3 between provenances differs (mainly due to different stomatal behaviors since only Tuscany plants partially avoided the uptake of the pollutant gas), both provenances showed detoxification and defense mechanisms; (iii) the crucial participation of phenylpropanoids, with a key role played by flavonoids (especially quercitrin): among this class of metabolites, isoquercitrin is the principal player in the lower O3 sensitivity of Tuscany plants, together with lignins; (iv) although coumarins (typical compounds of Fraxinus) were severely depressed by O3, isofraxidin was triggered suggesting a key role in reactive oxygen species (ROS) detoxification, as well as trans-chalcone. Furthermore, the different behavior of verbascoside and oleuropein among provenances lead us to speculate on their influence in the tentatively repair or acclimation shown by Piedmont plants at the end of the exposure. Finally, the intra-specific O3 sensitivity may be also due to de novo peaks triggered by O3 not yet associated to some chemicals