Impact of Scheduling in the Return-Link of Multi-Beam Satellite MIMO Systems

The utilization of universal frequency reuse in multi-beam satellite systems introduces a non-negligible level of co-channel interference (CCI), which in turn penalizes the quality of service experienced by users. Taking this as starting point, the paper focuses on resource management performed by the gateway (hub) on the return-link, with particular emphasis on a scheduling algorithm based on bipartite graph approach. The study gives important insights into the achievable per-user rate and the role played by the number of users and spot beams considered for scheduling. More interestingly, it is shown that a free-slot assignment strategy helps to exploit the available satellite resources, thus guaranteeing a max-min rate requirement to users. Remarks about the trade-off between efficiency-loss and performance increase are finally drawn at the end of the paper.Comment: Submitted and accepted to IEEE GLOBECOM 2012 Conference, 6 pages, 10 figure

Effective equilibrium picture in xy−xy-model with exponentially correlated noise

We study the effect of exponentially correlated noise on $xy-$model in the limit of small correlation time discussing the order-disorder transition in mean-field and the topological transition in two dimensions. We map the steady states of the non-equilibrium dynamics into an effective equilibrium theory. In mean-field, the critical temperature increases with the noise correlation time $\tau$ indicating that memory effects promote ordering. This finding is confirmed by numerical simulations. The topological transition temperature in two dimensions remains untouched. However, finite size effects induce a crossover in the vortices proliferation that is confirmed by numerical simulations

Effective potential method for active particles

We investigate the steady state properties of an active fluid modeled as an assembly of soft repulsive spheres subjected to Gaussian colored noise. Such a noise captures one of the salient aspects of active particles, namely the persistence of their motion and determines a variety of novel features with respect to familiar passive fluids. We show that within the so-called multidimensional unified colored noise approximation, recently introduced in the field of active matter, the model can be treated by methods similar to those employed in the study of standard molecular fluids. The system shows a tendency of the particles to aggregate even in the presence of purely repulsive forces because the combined action of colored noise and interactions enhances the the effective friction between nearby particles. We also discuss whether an effective two-body potential approach, which would allow to employ methods similar to those of density functional theory, is appropriate. The limits of such an approximation are discussed.Comment: 14 pages, 6 figures in Molecular Physics, 11 march 2016. arXiv admin note: text overlap with arXiv:cond-mat/0605094 by other author

Essays in Behavioural and Experimental Economics: Emotions, uncertainty and cooperation

In the present doctoral thesis I apply the experimental method in the context of two lines of research in Economics, the former investigating the role of incidental emotions in decision making under risk, whereas the latter shedding light on the impact of communication on cooperation. The dissertation consists of three sections. In the first chapter I conduct a laboratory experiment in order to study the effect of incidental sadness and happiness on risky decision making. An emotion induction procedure is the treatment variable of a between-subjects design where two sessions aim at eliciting either sadness or happiness, respectively. Two further groups are characterized by neutral conditions and serve as baseline. After a manipulation check verifies the validity of the induction procedure, I use a multiple price list `a la Holt and Laury (2002) to elicit individual risk preferences in the context of a lottery-choice task. The analysis reveals that both sadness and happiness promote greater risk aversion with respect to neutral conditions, a result which might be moderated by the risk elicitation task. Therefore, as effective explanation I propose the theory of ego depletion, whereby regulating emotions so as to subsequently process information consumes a limited self-control resource, which is needed to take risks as well. The second chapter is a meta-analysis of experimental studies on the same topic, so as to explain traditional heterogeneity of outcomes in the field. After performing an advanced search in Google Scholar and filtering out studies that do not match a list of selection criteria, I include 16 studies from which 46 observations are drawn at the treatment level. At this point, I code a set of moderator variables representing experimental protocols and calculate Cohen (1988)\u2019s d effect size as dependent variable of a weighted least squares (WLS) regression where larger studies are given more weight. Among the results, which are robust to different techniques for computing standard errors, I find that emotions induce higher risk aversion when a multiple price list `a la Holt and Laury (2002) is used in place of stated preferences methods, as well as in case the risk elicitation task is framed as an investment decision instead of an abstract choice. Given the variety of procedures employed in this type of experiments and in the absence of a tailor-made game to answer such research questions, I recommend faithful study replication as preferential path in order to investigate the influence of emotions on risky decision making and ensure comparability. The third chapter offers evidence on the impact of communication on the provision of public goods whose quality is uncertain. I run a laboratory experiment with two treatments, where the control variable is pre-play communication in the form of unrestricted text chat. A binary threshold public goods game with four-person groups and threshold of three is at the core of the design, the main novelty lying in the provision mechanism with ambiguity. Moreover, a private signal for the actual value of the public good is provided, before the contribution decision. In accordance with related literature, I find that communication significantly increases public good provision by reducing inefficiency that comes from wasteful undercontribution. Nevertheless, the players in the chat treatment seem to neglect the free-rider issue and often end up overcontributing, in contrast with previous scientific findings. After chat analysis, I propose the pursuit of symmetric payoffs within the group as original explanation of the massive overcontribution, in addition to group identity generated by the partner matching and the common fate hypothesis. Since the players prefer to minimize ambiguity than to maximize the group earnings, I finally speculate that under uncertainty satisficing is more salient than optimizing

Impact of urbanization on predator and parasitoid insects at multiple spatial scales

Landscapes are becoming increasingly urbanized, causing loss and fragmentation of natural habitats, with potentially negative effects on biodiversity. Insects are among the organisms with the largest diversity in urbanized environments. Here, we sampled predator (Ampulicidae, Sphecidae and Crabronidae) and parasitoid (Tachinidae) flower-visiting insects in 36 sites in the city of Rome (Italy). Although the diversity of herbivorous insects in urban areas mostly depends on the availability of flowering plants and nesting sites, predators and parasitoids generally require a larger number of resources during their life cycle, and are expected to be particularly influenced by urbanization. As flower-visitors can easily move between habitat patches, the effect of urbanization was tested at multiple spatial scales (local, landscape and sub-regional). We found that urbanization influenced predator and parasitoid flower-visitors at all three spatial scales. At the local scale, streets and buildings negatively influenced evenness of predators and species richness and abundance of parasitoids probably acting as dispersal barrier. At the landscape scale, higher percentage of urban decreased predator abundance, while increasing their evenness, suggesting an increase in generalist and highly mobile species. Area and compactness (i.e. Contiguity index) of urban green interactively influenced predator communities, whereas evenness of parasitoids increased with increasing Contiguity index. At the sub-regional scale, species richness and abundance of predators increased with increasing distance from the city center. Compared to previous studies testing the effect of urbanization, we found little variation in species richness, abundance and evenness along our urbanization gradient. The current insect fauna has been probably selected for its tolerance to habitat loss and fragmentation, being the result of the intensive anthropogenic alteration occurred in the area in the last centuries. Conservation strategies aimed at predator and parasitoid flying insects have to take in account variables at multiple spatial-scales, as well as the complementarity of resources across the landscape

Tire recycled rubber for more eco-sustainable advanced cementitious aggregate

This research focused on using ground tire rubber (GTR) with different grain sizes as a replacement for the mineral aggregates used in a cement-based mixture suitable for extrusion-based Additive Manufacturing. The use of two types of GTR particles and the possibility to apply rubberized mixtures in advanced manufacturing technologies are the innovative aspects of this work. At the base of this strategy is the possibility of achieving cementitious aggregates, which would potentially be improved regarding some technological-engineering requirements (lightness, thermal-acoustic insulation, energy dissipation capacity, durability) and environmentally sustainable. The integration of waste tires into cement-based materials is a promising solution for the reuse and recycling of such industrial waste. In addition, this approach may involve a considerable reduction in the use of natural resources (sand, water, coarse mineral aggregates) needed for the building materials production. The purpose of the research was to investigate the effect of sand-GTR replacement on certain chemical-physical properties of mixtures (permeable porosity, surface wetness, and water sorptivity), closely related to material durability. Besides, the role of rubber on the printability properties of the fresh material was evaluated. GTR fillers do not alter the rheological properties of the cement material, which was properly extruded with better print quality than the reference mixture. Concerning chemical-physical characterization, the GTR powder-granules synergy promotes good compaction of the mixture, hinders the cracks propagation in the cement matrix, decreases the permeable porosity, improves the surface hydrophobicity and preserves optimal water permeabilit

Anisotropic compression in the high pressure regime of pure and Cr-doped vanadium dioxide

We present structural studies of V$_{1-x}$Cr$_x$O$_2$ (pure, 0.7% and 2.5% Cr doped) compounds at room temperature in a diamond anvil cell for pressures up to 20 GPa using synchrotron x-ray powder diffraction. All the samples studied show a persistence of the monoclinic $M_1$ symmetry between 4 and 12 GPa. Above 12 GPa, the monoclinic $M_1$ symmetry changes to isostructural $M_x$ phase (space group $P2_1/c$) with a significant anisotropy in lattice compression of the $b$-$c$ plane of the $M_{1}$ phase. This behavior can be reconciled invoking the pressure induced charge-delocalization

Designing Robust API Monitoring Solutions

racing the sequence of library calls and system calls that a program makes is very helpful to characterize its interactions with the surrounding environment and, ultimately, its semantics. However, due to the entanglements of real-world software stacks, accomplishing this task can be surprisingly challenging as we take accuracy, reliability, and transparency into the equation. In this article, we identify six challenges that API monitoring solutions should overcome in order to manage these dimensions effectively and outline actionable design points for building robust API tracers that can be used even for security research. We then detail and evaluate SNIPER, an open-source API tracing system available in two variants based on dynamic binary instrumentation (for simplified in-guest deployment) and hardware-assisted virtualization (realizing the first general user-space tracer of this kind), respectively