4,688 research outputs found

    A Survey of Network Optimization Techniques for Traffic Engineering

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    TCP/IP represents the reference standard for the implementation of interoperable communication networks. Nevertheless, the layering principle at the basis of interoperability severely limits the performance of data communication networks, thus requiring proper configuration and management in order to provide effective management of traffic flows. This paper presents a brief survey related to network optimization using Traffic Engineering algorithms, aiming at providing additional insight to the different alternatives available in the scientific literature

    Renormalization-Group Approach to a Three-Legs Fermionic Ladder

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    We study the spin and charge phase diagram of a three-legs ladder (at zero temperature) as a function of fermion density and of transverse single-particle hopping by means of a Renormalization-Group analysis rigorously controlled in the weak-coupling limit. Periodic boundary conditions in the direction transverse to the ladder produce frustrated magnetic excitations yielding a spin-gapped phase in a large region about and at half filling. Spin correlations are instead enhanced when open transverse boundary conditions are considered, yielding an ungapped phase in a wide region about half filling (as observed in the Srn−1_{n-1}Cun+1_{n+1}O2n_{2n} stripes compounds) and at half filling down to a critical value of the transverse hopping t⊥t_{\perp}. At that critical value, the system undergoes a Mott transition at half filling by decreasing t⊥t_{\perp}.Comment: Final versio

    Out-of-plane dynamic response of a tuff masonry wall. Shaking table testing and numerical simulation

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    The out-of-plane dynamic response of a masonry element is investigated, both experimentally and numerically. The results of shaking table tests on a tuff masonry wall, subjected to harmonic acceleration histories, are presented. An isotropic nonlocal damage-plastic model, accounting for the masonry strength-stiffness degrading and hysteresis mechanisms, is introduced in a finite element procedure to numerically describe the masonry structural response. A simplified scheme is analysed, where the wall is completely restrained at the base and free at the top. The measured top displacement history is compared with that numerically evaluated, obtaining a satisfactory agreement. Moreover, the effects of the onset and evolution of the degrading mechanisms in the masonry wall are highlighted

    Direct role of structural dynamics in electron-lattice coupling of superconducting cuprates

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    The mechanism of electron pairing in high-temperature superconductors is still the subject of intense debate. Here, we provide direct evidence of the role of structural dynamics, with selective atomic motions (buckling of copper–oxygen planes), in the anisotropic electron-lattice coupling. The transient structures were determined using time-resolved electron diffraction, following carrier excitation with polarized femtosecond heating pulses, and examined for different dopings and temperatures. The deformation amplitude reaches 0.5% of the c axis value of 30 Å when the light polarization is in the direction of the copper–oxygen bond, but its decay slows down at 45°. These findings suggest a selective dynamical lattice involvement with the anisotropic electron–phonon coupling being on a time scale (1–3.5 ps depending on direction) of the same order of magnitude as that of the spin exchange of electron pairing in the high-temperature superconducting phase

    On the instability and constraints of the interaction between number representation and spatial attention in healthy humans. A concise review of the literature and new experimental evidence

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    .The relationship between number and space representation is still one of the most debated topics in studies of mathematical cognition. Here we offer a concise review of two important behavioral effects that have pointed out the use of a spatially left-to-right oriented mental number line (MNL) in healthy participants: the SNARC effect and the attentional SNARC effect (Att-SNARC). Following a brief summary of seminal investigations on the introspective properties of the MNL, we review recent empirical evidence and theories on the functional origin of the SNARC effect, where upon left/right response choices faster reaction times are found for small numbers with left-side responses and for large numbers with right-side responses. Then we offer a summary of the studies that have investigated whether the mere perception of visual Arabic numbers presented at central fixation can engender spatially congruent lateral shifts of attention, ie, leftward for small numbers and rightward for large ones, ie, the Att-SNARC effect. Finally, we summarize four experiments that tested whether the Att-SNARC depends on an active rather than passive processing of centrally presented digit cues. In line with other recent studies, these experiment do not replicate the original Att-SNARC and show that the mere perception of Arabic numerals does not trigger automatic shifts of attention. These shifts are instead found when the task requires the explicit left/right spatial coding of digit cues, ie, Spatial Att-SNARC (Fattorini et al., 2015b). Nonetheless, the reliability of the Spatial Att-SNARC effect seems not as strong as that of conventional SNARC effects where left/ right codes are mapped onto responses rather than directly mapped on digit cues. Comparing the magnitude of digits to a numerical reference, ie, "5," also produced a Magnitude Comparison Att-SNARC that was weaker than the spatial one. However, the reliability of this Magnitude Comparison Att-SNARC should be considered with caution because, like in a study by Zanolie and Pecher (2014), we recently failed to replicate this effect in a separate behavioral-eventrelated potentials study in preparation (Fattorini et al., 2015a). All together the results from the present series of experiments support the hypothesis that spatial coding is not an intrinsic part of number representation and that number-space interaction is determined by the use of stimulus-or response-related spatial codes in the task at han

    A GIS tool for the land carrying capacity of large solar plants

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    A tool for the estimation of the land carrying capacity of large solar plants, such as ground-mounted PV plants or solar thermal plants, is developed in GIS environment. The scope is to verify to what extent the constraints that governments and authorities have imposed on the construction of new large ground-mounted soalr plants affect the future developments of PV. The tool is applied to a large study area of North-Italy and specifically to solar photovoltaic plants but the results can be easily generalized to include large solar thermal plants. The peculiarity of the tool development is that both qualitative and quantitative criteria are merged together in order to obtain the final indicator, and that the weight of the objective function are estimated by means of an ANN. The available area are very limited and strongly influenced by the normative qualitative criteria (restricted areas)

    Energy performance and indoor environmental control of animal houses: a modelling tool

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    The energy-related products Directive (ErP) 2009/125/EC has set a new generation of equipment that are more energy efficient and reliable. In the case of climate control for livestock housing, a key role can be played by EC motors direct drive variable flow fans that can be used instead of traditional AC fans in applications like broiler or dairy houses. The energy consumptions of such fans strictly depend on the specific application and on the outdoor weather conditions, and there is therefore the need to forecast their energy performance by means of computational tools. In this work, we present a tool developed by the Authors and based on a dynamic model for the estimation of the global (electricity, natural gas, etc.) annual energy consumption of a system installed into an animal house. The calculation is based on a customization of the ISO 13790 Standard simplified hourly model for the energy performance assessment of broiler houses

    Students' knowledge and perceptions of International Relations and the 'Model United Nations'. An empirical analysis

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    open2Unconventional learning activities such as games and simulations have been widely used as teaching tools in international relations (IR) in the recent years. The literature on simulations and student learning has often highlighted a lack of empirical evidence in the existing research. The paper aims at providing empirical support to illustrate the ways in which simulations might influence students’ levels of (factual and self-evaluated) knowledge and perceptions of IR. The study is based on extensive empirical material, collected through questionnaires submitted to 298 students who participated in the 2014 edition of the National Model United Nations in New York (NMUN!NY)openCalossi, Enrico, Coticchia, FabrizioCalossi, Enrico; Coticchia, Fabrizi

    Building Design for Energy Efficient Livestock Housing

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    Energy usage on farms is considered direct when used to operate machinery and climate control systems or indirect when is used to manufacture feed and agro- chemicals. Direct on-farm energy consumption was estimated to be 6 EJ yr− 1, representing about 1.2% of total world energy consumption (OECD, 2008). If indirect energy is included, total farm energy consumption could be as much as 15 EJ yr− 1, representing about 3.1% of global energy consumption. Housed livestock require adequate indoor climate conditions to maximize both production and welfare, particularly avoiding thermal stress. The task of the engineer is to improve the energy use efficiency of livestock housing and to minimize energy consumption. This can be achieved by improving the energy performance of the equipment used for climate control and the design of the building.The focus of this chapter is on building design for efficient energy manage-ment in livestock housing. Improving building design requires understanding the mass and energy balance of the system to specify materials, dimensions, and equipment needed to maintain safe operating conditions. The importance of understanding the energy needs of buildings is illustrated by the report of St-Pierre et al. (2003), who estimated the economic losses by the dairy industry in the U.S. at 1.69to1.69 to 2.36 billion annually due to heat stress. Understanding and being able to use fundamental concepts for animal housing design provides the foundation for desirable welfare and more efficient production- centric animal housing

    Methodologies and advancements in the calibration of building energy models

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    Buildings do not usually perform during operation as well as predicted during the design stage. Disagreement between simulated and metered energy consumption represents a common issue in building simulation. For this reason, the calibration of building simulation models is of growing interest. Sensitivity and uncertainty analyses play an important role in building model accuracy. They can be used to identify the building model parameters most influent on the energy consumption. Given this, these analyses should be integrated within calibration methodologies and applications for tuning the parameters. This paper aims at providing a picture of the state of the art of calibration methodologies in the domain of building energy performance assessment. First, the most common methodologies for calibration are presented, emphasizing criticalities and gaps that can be faced. In particular the main issues to be addressed, when carrying out calibrated simulation, are discussed. The standard statistical criteria for considering the building models calibrated and for evaluating their goodness-of-fit are also presented. Second, the commonly used techniques for investigating uncertainties in building models are reviewed. Third, a review of the latest main studies in the calibrated simulation domain is presented. Criticalities and recommendations for new studies are finally provided
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