Showing papers by "Polytechnic University of Turin published in 2009"
TL;DR: In this article, the extended and generalized finite element methods are reviewed with an emphasis on their applications to problems in material science: fracture, dislocations, grain boundaries and phase interfaces.
Abstract: The extended and generalized finite element methods are reviewed with an emphasis on their applications to problems in material science: (1) fracture, (2) dislocations, (3) grain boundaries and (4) phases interfaces. These methods facilitate the modeling of complicated geometries and the evolution of such geometries, particularly when combined with level set methods, as for example in the simulation growing cracks or moving phase interfaces. The state of the art for these problems is described along with the history of developments.
718 citations
TL;DR: In this paper, the authors present the main aspects of the DMG framework, illustrating its characteristics and summarizing the relevant DMG structures, backed by an extended review of the most recent journal publications and reports.
Abstract: The recent development of efficient thermal prime movers for distributed generation is changing the focus of the production of electricity from large centralized power plants to local generation units scattered over the territory. The scientific community is addressing the analysis and planning of distributed energy resources with widespread approaches, taking into account technical, environmental, economic and social issues. The coupling of cogeneration systems to absorption/electric chillers or heat pumps, as well as the interactions with renewable sources, allow for setting up multi-generation systems for combined local production of different energy vectors such as electricity, heat (at different enthalpy levels), cooling power, hydrogen, various chemical substances, and so forth. Adoption of composite multi-generation systems may lead to significant benefits in terms of higher energy efficiency, reduced CO2 emissions, and enhanced economy. In this light, a key direction for improving the characteristics of the local energy production concerns the integration of the concepts of distributed energy resources and combined production of different energy vectors into a comprehensive distributed multi-generation (DMG) framework that entails various approaches to energy planning currently available in the literature. This paper outlines the main aspects of the DMG framework, illustrating its characteristics and summarizing the relevant DMG structures. The presentation is backed by an extended review of the most recent journal publications and reports.
638 citations
TL;DR: In this article, a detailed LCA model was set-up, based on field measured data from an urban area under demolition and re-design, paying attention to the end-of-life phase and supplying actual data on demolition and rubble recycling.
425 citations
TL;DR: In this article, the chemical and physical properties of the MWCNTs were analyzed by means of EDX, TGA, SEM, and Raman analysis, and the phase composition of the composites were characterized by using an X-ray diffractometer and scanning electron microscope.
398 citations
TL;DR: In this paper, the authors survey the relevant theoretical and empirical literature on the relationship between regulation, at both retail and wholesale level, and investment in telecoms infrastructures, and conclude that the picture that emerges is not conclusive, and further research is still needed, both theoretically and empirically, to better understand the real impact of regulatory incentives on investments.
385 citations
TL;DR: The electric current activated/assisted sintering (ECAS) is an ever growing class of versatile techniques for sinterding particulate materials as discussed by the authors. But despite the tremendous advances over the last two decades in ECASed materials and products, there is a lack of comprehensive reviews on ECAS apparatuses and methods.
383 citations
TL;DR: The analysis shows the potential for an early epidemic peak occurring in October/November in the Northern hemisphere, likely before large-scale vaccination campaigns could be carried out, and suggests that the planning of additional mitigation policies such as systematic antiviral treatments might be the key to delay the activity peak in order to restore the effectiveness of the vaccination programs.
Abstract: On 11 June the World Health Organization officially raised the phase of pandemic alert (with regard to the new H1N1 influenza strain) to level 6. As of 19 July, 137,232 cases of the H1N1 influenza strain have been officially confirmed in 142 different countries, and the pandemic unfolding in the Southern hemisphere is now under scrutiny to gain insights about the next winter wave in the Northern hemisphere. A major challenge is pre-empted by the need to estimate the transmission potential of the virus and to assess its dependence on seasonality aspects in order to be able to use numerical models capable of projecting the spatiotemporal pattern of the pandemic. In the present work, we use a global structured metapopulation model integrating mobility and transportation data worldwide. The model considers data on 3,362 subpopulations in 220 different countries and individual mobility across them. The model generates stochastic realizations of the epidemic evolution worldwide considering 6 billion individuals, from which we can gather information such as prevalence, morbidity, number of secondary cases and number and date of imported cases for each subpopulation, all with a time resolution of 1 day. In order to estimate the transmission potential and the relevant model parameters we used the data on the chronology of the 2009 novel influenza A(H1N1). The method is based on the maximum likelihood analysis of the arrival time distribution generated by the model in 12 countries seeded by Mexico by using 1 million computationally simulated epidemics. An extended chronology including 93 countries worldwide seeded before 18 June was used to ascertain the seasonality effects. We found the best estimate R
0 = 1.75 (95% confidence interval (CI) 1.64 to 1.88) for the basic reproductive number. Correlation analysis allows the selection of the most probable seasonal behavior based on the observed pattern, leading to the identification of plausible scenarios for the future unfolding of the pandemic and the estimate of pandemic activity peaks in the different hemispheres. We provide estimates for the number of hospitalizations and the attack rate for the next wave as well as an extensive sensitivity analysis on the disease parameter values. We also studied the effect of systematic therapeutic use of antiviral drugs on the epidemic timeline. The analysis shows the potential for an early epidemic peak occurring in October/November in the Northern hemisphere, likely before large-scale vaccination campaigns could be carried out. The baseline results refer to a worst-case scenario in which additional mitigation policies are not considered. We suggest that the planning of additional mitigation policies such as systematic antiviral treatments might be the key to delay the activity peak in order to restore the effectiveness of the vaccination programs.
382 citations
TL;DR: In this paper, an extensive analysis of deterministic and stochastic mechanisms for the formation of vegetation patterns is presented, along with some examples of applications relevant to the environmental sciences.
Abstract: [1] Highly organized vegetation patterns can be found in a number of landscapes around the world. In recent years, several authors have investigated the processes underlying vegetation pattern formation. Patterns that are induced neither by heterogeneity in soil properties nor by the local topography are generally explained as the result of spatial self-organization resulting from “symmetry-breaking instability” in nonlinear systems. In this case, the spatial dynamics are able to destabilize the homogeneous state of the system, leading to the emergence of stable heterogeneous configurations. Both deterministic and stochastic mechanisms may explain the self-organized vegetation patterns observed in nature. After an extensive analysis of deterministic theories, we review noise-induced mechanisms of pattern formation and provide some examples of applications relevant to the environmental sciences.
328 citations
TL;DR: The tolerance of electric power grids to both accidental and malicious outages is analyzed in the framework of complex network theory, and the quantity known as efficiency is modified by introducing a new concept of distance between nodes called net-ability.
Abstract: Power grids exhibit patterns of reaction to outages similar to complex networks. Blackout sequences follow power laws, as complex systems operating near a critical point. Here, the tolerance of electric power grids to both accidental and malicious outages is analyzed in the framework of complex network theory. In particular, the quantity known as efficiency is modified by introducing a new concept of distance between nodes. As a result, a new parameter called net-ability is proposed to evaluate the performance of power grids. A comparison between efficiency and net-ability is provided by estimating the vulnerability of sample networks, in terms of both the metrics.
309 citations
TL;DR: In this paper, the addition of nanoclays was found to increase the PLA degradation rate, especially for the highest dispersed clay in the polymer matrix, and it was also found that clays can influence the polymer bacterial degradation depending on their chemical structure and affinity of the bacterium towards the clay.
303 citations
TL;DR: In this article, a wide angle X-ray analysis (WAXS) was performed on PLA and PCL nanocomposites and the results showed a good dispersion level with both polymeric matrices, whilst the highest thermo-mechanical improvements were reached depending on type of clay.
TL;DR: In this paper, the performance of a prototype of a high pressure polymer electrolyte membrane water electrolyser was analyzed using the Italian FISR (Research special supplementary funding) project.
TL;DR: In this article, a survey of plate/shell analysis is presented, where the authors evaluate a large variety of plate theories to evaluate the bending and vibration of sandwich structures, including classical, higher order, zigzag, layerwise, and mixed theories.
Abstract: A large variety of plate theories are described and assessed in the present work to evaluate the bending and vibration of sandwich structures. A brief survey of available works is first given. Such a survey includes significant review papers and latest developments on sandwich structure modelings. The kinematics of classical, higher order, zigzag, layerwise, and mixed theories is described. An exhaustive numerical assessment of the whole theories is provided in the case of closed form solutions of simply supported panels made of orthotropic layers. Reference is made to the unified formulation that has recently been introduced by the first author for a plate/shell analysis. Attention has been given to displacements, stresses (both in-plane and out-of-plane components), and the free vibration response. Only simply supported orthotropic panels loaded by a transverse distribution of bisinusoidal pressure have been analyzed. Five benchmark problems are treated. The accuracy of the plate theories is established with respect to the length-to-thickness-ratio (LTR) geometrical parameters and to the face-to-core-stiffness-ratio (FCSR) mechanical parameters. Two main sources of error are outlined, which are related to LTR and FCSR, respectively. It has been concluded that higher order theories (HOTs) can be conveniently used to reduce the error due to LTR in thick plate cases. But HOTs are not effective in increasing the accuracy of the classical theory analysis whenever the error is caused by increasing FCSR values; layerwise analysis becomes mandatory in this case.
TL;DR: A simple and effective adaptation is proposed that is able to preserve the average of states and to drive the system near to the consensus value, when a uniform quantization is applied to communication between agents.
Abstract: This work presents a contribution to the solution of the average agreement problem on a network with quantized links. Starting from the well-known linear diffusion algorithm, we propose a simple and effective adaptation that is able to preserve the average of states and to drive the system near to the consensus value, when a uniform quantization is applied to communication between agents. The properties of this algorithm are investigated both by a worst-case analysis and by a probabilistic analysis, and are shown to depend on the spectral properties of the evolution matrix. A special attention is devoted to the issue of the dependence of the performance on the number of agents, and several examples are given. Copyright © 2008 John Wiley & Sons, Ltd.
TL;DR: LCA has proved to be an effective tool for understanding the eco-profile of Italian rice and should be used for transparent and credible communication between suppliers and their customers.
TL;DR: One signal captures most of the underlying variability of the low‐frequency components of motor unit discharge rates and explains large part of the fluctuations in the motor output during isometric contractions.
Abstract: The aim of the study was to investigate the relation between linear transformations of motor unit discharge rates and muscle force. Intramuscular (wire electrodes) and high-density surface EMG (13 × 5 electrode grid) were recorded from the abductor digiti minimi muscle of eight healthy men during 60 s contractions at 5%, 7.5% and 10% of the maximal force. Spike trains of a total of 222 motor units were identified from the EMG recordings with decomposition algorithms. Principal component analysis of the smoothed motor unit discharge rates indicated that one component (first common component, FCC) described 44.2 ± 7.5% of the total variability of the smoothed discharge rates when computed over the entire contraction interval and 64.3 ± 10.2% of the variability when computed over 5 s intervals. When the FCC was computed from four or more motor units per contraction, it correlated with the force produced by the muscle (62.7 ± 10.1%) by a greater degree (P < 0.001) than the smoothed discharge rates of individual motor units (41.4 ± 7.8%). The correlation between FCC and the force signal increased up to 71.8 ± 13.1% when the duration and the shape of the smoothing window for discharge rates were similar to the average motor unit twitch force. Moreover, the coefficients of variation (CoV) for the force and for the FCC signal were correlated in all subjects (R2 range = 0.14–0.56; P < 0.05) whereas the CoV for force was correlated to the interspike interval variability in only one subject (R2= 0.12; P < 0.05). Similar results were further obtained from measures on the tibialis anterior muscle of an additional eight subjects during contractions at forces up to 20% of the maximal force (e.g. FCC explained 59.8 ± 11.0% of variability of the smoothed discharge rates). In conclusion, one signal captures most of the underlying variability of the low-frequency components of motor unit discharge rates and explains large part of the fluctuations in the motor output during isometric contractions.
TL;DR: The capability of the Convolution Kernel Compensation (CKC) method to identify motor unit (MU) discharge patterns from the simulated and experimental surface electromyogram (sEMG) during low-force contractions was tested.
29 Sep 2009
TL;DR: In this article, an integral battery charger for an electric scooter with high voltage batteries and interior-permanent-magnet motor traction drive is presented, which is derived from the power hardware of the scooter, with the ac motor drive that operates as three phase boost rectifier with power factor correction capability.
Abstract: This paper presents an integral battery charger for an electric scooter with high voltage batteries and interior-permanent-magnet motor traction drive. The battery charger is derived from the power hardware of the scooter, with the ac motor drive that operates as three-phase boost rectifier with power factor correction capability. The control of the charger is also integrated into the scooter control firmware that is implemented on a fixed-point DSP controller. Current-controlled or voltage-controlled charge modes are actuated according to the requirements of the battery management system, that is embedded into the battery pack. With respect to previous integrated chargers, the ac current is absorbed at unitary power factor with no harmonic distortion. Moreover, no additional filtering is needed since the pulsewidth modulation ripple is minimized by means of phase interleaving. The feasibility of the integral charger with different ac motors (induction motor, surface-mounted phase modulation motor) is also discussed, by means of a general model purposely developed for three-phase ac machines. The effectiveness of the proposed battery charger is experimentally demonstrated on a prototype electric scooter, equipped with two Li-ion battery packs rated 260 V, 20 Ah.
TL;DR: In this paper, a systematic investigation on Mg-substituted hydroxyapatite (Ca 10− x Mg x (PO 4 ) 6 (OH) 2 ) nanopowders produced by precipitation of Ca(NO 3 ) 2 ·4H 2 O and Mg(NO3 ) 2.
Abstract: This paper reports a systematic investigation on Mg-substituted hydroxyapatite (Ca 10− x Mg x (PO 4 ) 6 (OH) 2 ) nanopowders produced by precipitation of Ca(NO 3 ) 2 ·4H 2 O and Mg(NO 3 ) 2 . The Mg content ranged between 0.6 and 2.4 wt%. Semicrystalline Mg-substituted hydroxyapatite powders made up of needle-like nanoparticles were obtained, the specific surface area ranged between 87 and 142 m 2 /g. Pure hydroxyapatite nanopowder decomposed around 1000 °C. Mg-substituted hydroxyapatites were thermally stable up to 660 °C ( x = 1.0), 760 °C ( x = 0.5) and 840 °C ( x = 0.25) showing a distinct decreased thermal stability with respect to the pure sample. A relevant displacement of the sintering curve at lower temperature as a function of Mg content was observed, comparing to the behaviour of a pure HAp material, synthesized following the same procedure, and ascribed to the β-TCP formation.
TL;DR: An extended topological approach is proposed that includes the definitions of traditional topological metrics as well as the physical/operational behavior of power grids in terms of real power-flow allocation over lines and line flow limits and provides two new metrics, entropic degree and net-ability, that can be used to assess structural vulnerabilities in power systems.
01 Nov 2009
TL;DR: In this paper, the authors present the most challenging application of electric machines and drives in the incoming new aircraft generation system, focusing on the most safety critical drives: flight surface actuators, fuel pumps and generators.
Abstract: In order to improve aircraft efficiency, reliability and maintainability, the aerospace world has found in the progressive electrification of on-board services the way to reduce or to remove the presence of the hydraulic, mechanical and the bleed air/pneumatic systems. This concept is called More Electric Aircraft (MEA), which involves the introduction of the Electromechanical actuators (EMAs) and the electro-hydraulics actuators (EHAs) for the actuation of the flight surfaces of wide-body aircraft, moving from the “fly-by wire” to the “power-by wire” concept. The resulting step change in aircraft electrical loading will have far reaching implications for the electrical generation system. Considerable effort is being directed towards realizing the so-called More Electric Engine (MEE), which foresee an integration of the electrical generator directly inside the main gas turbine engine. Also the entire electrical distribution system is subject to radical revisiting, with a trend which is leaving the constant frequency AC energy distribution in favor of variable frequency or DC solutions. Hence, it is evident the MEA trend increments the technical challenges and research topics for the electrical engineering in the aeronautic applications. The aim of the paper is the presentation, from the electrical engineering point of view, of some of the most challenging application of electric machines and drives in the incoming new aircraft generation. There are too many on board electric components and systems to be analyzed: the authors centre the attention on the most safety critical drives: flight surface actuators, fuel pumps and generators.
TL;DR: The model presented in this article focuses mainly on the description of mechanical interactions of the growing tumour with the host tissue, their influence on tumour growth, and the attachment/detachment mechanisms between cells and ECM.
Abstract: Resorting to a multiphase modelling framework, tumours are described here as a mixture of tumour and host cells within a porous structure constituted by a remodelling extracellular matrix (ECM), which is wet by a physiological extracellular fluid. The model presented in this article focuses mainly on the description of mechanical interactions of the growing tumour with the host tissue, their influence on tumour growth, and the attachment/detachment mechanisms between cells and ECM. Starting from some recent experimental evidences, we propose to describe the interaction forces involving the extracellular matrix via some concepts coming from viscoplasticity. We then apply the model to the description of the growth of tumour cords and the formation of fibrosis.
TL;DR: This study shows that the quantification of helical blood flow in vivo is feasible, and it might allow detection of anomalies in the expected physiological development of helicals flow in aorta and accordingly, could be used in a diagnostic/prognostic index for clinical practice.
Abstract: The mechanics of blood flow in arteries plays a key role in the health of individuals. In this framework, the role played by the presence of helical flow in the human aorta is still not clear in its relation to physiology and pathology. We report here a method for quantifying helical flow in vivo employing time-resolved cine phase contrast magnetic resonance imaging to obtain the complete spatio-temporal description of the three-dimensional pulsatile blood flow patterns in aorta. The method is applied to data of one healthy volunteer. Particle traces were calculated from velocity data: to them we applied a Lagrangian-based method for helical flow quantification, the Helical Flow Index, which has been developed and evaluated in silico in order to reveal global organization of blood flow. Our results: (i) put in evidence that the systolic hemodynamics in aorta is characterized by an evolving helical flow (we quantified a 24% difference in terms of the content of helicity in the streaming blood, between mid and early systole); (ii) indicate that in the first part of the systole helicity is ascrivable mainly to the asymmetry of blood flow in the left ventricle, joined with the laterality of the aorta. In conclusion, this study shows that the quantification of helical blood flow in vivo is feasible, and it might allow detection of anomalies in the expected physiological development of helical flow in aorta and accordingly, could be used in a diagnostic/prognostic index for clinical practice.
TL;DR: In this article, the authors investigated the transport of iron nanoparticle suspensions, bare or modified with the green polymer guar gum, in a water saturated sand-packed columns and found that bare iron nanoparticles are basically immobile in sandy porous media.
Abstract: In order to ensure adequate mobility of zerovalent iron nanoparticles in natural aquifers, the use of a stabilizing agent is necessary. Polymers adsorbed on the nanoparticle surface will give rise to electrosteric stabilization and will decrease attachment to the surface soil grains. Water saturated sand-packed columns were used in this study to investigate the transport of iron nanoparticle suspensions, bare or modified with the green polymer guar gum. The suspensions were prepared at 154 mg/L particle concentration and 0.5 g/L polymer concentration. Transport experiments were conducted by varying the ionic strength, ionic composition, and approach velocity of the fluid. Nanoparticle deposition rates, attachment efficiencies, and travel distances were subsequently calculated based on the classical particle filtration theory. It was found that bare iron nanoparticles are basically immobile in sandy porous media. In contrast, guar gum is able to ensure significant nanoparticle transport at the tested conditions, regardless of the chemistry of the solution. Attachment efficiency values for guar gum-coated nanoparticles under the various conditions tested were smaller than 0.066. Although the calculated travel distances may not prove satisfactory for field application, the investigation attested the promising role of guar gum to ensure mobility of iron nanoparticles in the subsurface environment.
07 Oct 2009
TL;DR: The design, development and experimental evaluation of gt, an open source software toolset for associating ground truth information with Internet traffic traces, show that gt's effectiveness comes at little cost in terms of overhead on the hosting machines.
Abstract: Much of Internet traffic modeling, firewall, and intrusion detection research requires traces where some ground truth regarding application and protocol is associated with each packet or flow. This paper presents the design, development and experimental evaluation of gt, an open source software toolset for associating ground truth information with Internet traffic traces. By probing the monitored host's kernel to obtain information on active Internet sessions, gt gathers ground truth at the application level. Preliminary experimental results show that gt's effectiveness comes at little cost in terms of overhead on the hosting machines. Furthermore, when coupled with other packet inspection mechanisms, gt can derive ground truth not only in terms of applications (e.g., e-mail), but also in terms of protocols (e.g., SMTP vs. POP3).
TL;DR: In this article, the authors present a comprehensive input-output matrix approach aimed at modelling small-scale trigeneration equipment taking into account the interactions among plant components and external energy networks.
TL;DR: Two issues in the extended finite element method (XFEM) are addressed: efficient numerical integration of the weak form when the enrichment function is self‐equilibrating and blending of the enrichment.
Abstract: Two issues in the extended finite element method (XFEM) are addressed: efficient numerical integration of the weak form when the enrichment function is self-equilibrating and blending of the enrichment. The integration is based on transforming the domain integrals in the weak form into equivalent contour integrals. It is shown that the contour form is computationally more efficient than the domain form, especially when the enrichment function is singular and/or discontinuous. A method for alleviating the errors in the blending elements is also studied. In this method, the enrichment function is pre-multiplied by a smooth weight function with compact support to allow for a completely smooth transition between enriched and unenriched subdomains. A method for blending step function enrichment with singular enrichments is described. It is also shown that if the enrichment is not shifted properly, the weighted enrichment is equivalent to the standard enrichment. An edge dislocation and a crack problem are used to benchmark the technique; the influence of the variables that parameterize the weight function is analyzed. The resulting method shows both improved accuracy and optimum convergence rates and is easily implemented into existing XFEM codes
TL;DR: It is demonstrated that highly concentrated NZVI slurries can be stabilized for more than 10 days adding 6g/L of xanthan gum biopolymer, mainly due to the formation of a viscous gel characterized by shear-thinning behaviour.
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TL;DR: This paper considers the average consensus problem on a network of digital links, and proposes a set of algorithms based on pairwise ''gossip'' communications and updates, which study the convergence properties of such algorithms with the goal of answering two design questions.
Abstract: This paper considers the average consensus problem on a network of digital links, and proposes a set of algorithms based on pairwise ''gossip'' communications and updates. We study the convergence properties of such algorithms with the goal of answering two design questions, arising from the literature: whether the agents should encode their communication by a deterministic or a randomized quantizer, and whether they should use, and how, exact information regarding their own states in the update.