4,289 research outputs found
TMsim : an algorithmic tool for the parametric and worst-case simulation of systems with uncertainties
This paper presents a general purpose, algebraic tool—named TMsim—for the combined parametric and worst-case analysis of systems with bounded uncertain parameters.The tool is based on the theory of Taylor models and represents uncertain variables on a bounded domain in terms of a Taylor polynomial plus an interval remainder accounting for truncation and round-off errors.This representation is propagated from inputs to outputs by means of a suitable redefinition of the involved calculations, in both scalar and matrix form. The polynomial provides a parametric approximation of the variable, while the remainder gives a conservative bound of the associated error. The combination between the bound of the polynomial and the interval remainder provides an estimation of the overall (worst-case) bound of the variable. After a preliminary theoretical background, the tool (freely available online) is introduced step by step along with the necessary theoretical notions. As a validation, it is applied to illustrative examples as well as to real-life problems of relevance in electrical engineering applications, specifically a quarter-car model and a continuous time linear equalizer
Changing the University System Management: a study of the Italian scenario
Over recent years, the Italian University System has been handling a phase of deep
changes, which have had significant impact on its mission and on the way it operates.
The most important of these changes have been to the organisation of universities, their
recruitment procedures and in terms of improvements to the quality and efficiency of
the university system itself. In this perspective, the objective of this research was to carry
out a critical analysis of the process of change, with special reference to improving
efficiency by making the transition from cash-based accounting to accrual accounting. In
order to achieve this objective, the starting point was the legislation of reference that
sets out the terms for the move to financial accrual accounting. A comparative analysis
was then carried out at an international level, with the purpose of highlighting the
strengths and weaknesses identified during the implementation of these new
procedures within the public field. This was followed by an analysis of the details of the
theory defining the accounting principles to be used in the process of preparing
university’s financial statements. Finally, the study identified the main critical points
relating to implementation of the new accounting system, offering, at the same time,
several thoughts concerning possible subsequent analyses on this topic
Comparison of Stochastic Methods for the Variability Assessment of Technology Parameters
This paper provides and compares two alternative solutions for the simulation of cables and interconnects with the inclusion of the effects of parameter uncertainties, namely the Polynomial Chaos (PC) method and the Response Surface Modeling (RSM). The problem formulation applies to the telegraphers equations with stochastic coefficients. According to PC, the solution requires an expansion of the unknown parameters in terms of orthogonal polynomials of random variables. On the contrary, RSM is based on a least-square polynomial fitting of the system response. The proposed methods offer accuracy and improved efficiency in computing the parameter variability effects on system responses with respect to the conventional Monte Carlo approach. These approaches are validated by means of the application to the stochastic analysis of a commercial multiconductor flat cable. This analysis allows us to highlight the respective advantages and disadvantages of the presented method
Comment on "Interaction of two solitary waves in quantum electron-positron-ion plasma" [Phys. Plasmas \textbf{18}, 052301 (2011)]
Recently, Yan-Xia Xu, et al. in the article Ref. [Phys. Plasmas \textbf{18},
052301 (2011)] have studied the effects of various plasma parameters on
interaction of two ion-acoustic solitary waves in an unmagnetized
three-dimensional electron-positron-ion quantum plasma. They have used the
extended reductive perturbation technique, the so-called, extended
Poincare'-Lighthill-Kuo (PLK) technique, to deduce from the model governing the
quantum hydrodynamics (QHD) differential equations leading to the soliton
dynamical properties, namely, Korteweg-de Vries evolution equations (one for
each wave) and coupled differential equations describing the phase-shift in
trajectories of solitons due to the two dimensional collision. The variation of
the calculated collision phase-shifts are then numerically inspected in terms
of numerous plasma fractional parameters. In this comment we give some notes
specific to the validity of the results of above-mentioned article and refer to
important misconceptions about the use of the Fermi-temperature in quantum
plasmas, appearing in this article and many other recently published ones.Comment: Accepted Journal Physics of Plasma
Pathological Behavior in the Spectral Statistics of the Asymmetric Rotor Model
The aim of this work is to study the spectral statistics of the asymmetric
rotor model (triaxial rigid rotator). The asymmetric top is classically
integrable and, according to the Berry-Tabor theory, its spectral statistics
should be Poissonian. Surprisingly, our numerical results show that the nearest
neighbor spacing distribution and the spectral rigidity do
not follow Poisson statistics. In particular, shows a sharp peak at
while for small values of follows the Poissonian
predictions and asymptotically it shows large fluctuations around its mean
value. Finally, we analyze the information entropy, which shows a dissolution
of quantum numbers by breaking the axial symmetry of the rigid rotator.Comment: 11 pages, 7 figures, to be published in Phys. Rev.
The impact of the reform of the milk quota regime on the Italian dairy sector
This paper analyses the impact of the milk quota regime reform, actually under discussion, on the European countries with a detailed focus on the Italian milk and dairy sector. The dismantling of the milk quota regime is already on the EU agenda, but how and when to do it is still matter of debate. A possibility is to enlarge gradually the size of the national quotas, up to the full dismantling in 2015 (“soft landing”). Meanwhile, the discussion on Health Check of the CAP is under way. In this work we analyse the possible impacts of the reform of the milk quota regime on the basis of a Computable General Equilibrium (CGE) approach, using two models in sequence: the Global Trade Analysis Project (GTAP) model is used to evaluate the impacts of different scenarios of milk quota reform on the EU market and to compute the price changes outside Italy; these, in turn, are used as inputs for the MEG-D model, that focuses on the Italian milk and dairy market. The two models were run together with two specific objectives: the first was to avoid, in evaluating the impacts of reform of the milk sector regime in Italy, running the model with rough price estimates taken for secondary sources; the second, to have more specific results on the outcome at the national level. Particularly, the model takes in account the particular relevance of quality products (GDO) in Italian diary sector. In order to evaluate the impact of the “soft landing” reform scenario, we run a “comparison” scenario where the milk quotas are fully abolished in the 2009.Milk and dairy sector, Quota production, EU Agri-Food Market, PAC, Agricultural and Food Policy, Livestock Production/Industries,
Consensus for nonlinear monotone networks with unilateral interactions
This paper deals with an extended framework of the distributed asymptotic agreement problem by allowing the presence of unilateral interactions (optimistic or pessimistic) in place of bilateral ones, for a large class of nonlinear monotone time-varying networks. In this original setup we firstly introduce notions of unilateral optimistic and/or pessimistic interaction, of associated bicolored edge in the interaction graph and a suitable graph-theoretical connectedness property. Secondly, we formulate a new assumption of integral connectivity and show that it is sufficient to guarantee exponential convergence towards the agreement subspace. Finally, we remark that the proposed conditions are also necessary for consensuability. Theoretical advances are emphasized through illustrative examples given both to support the discussion and to highlight how the proposed framework extends all existing conditions for consensus of monotone networks
Social contact structures and time use patterns in the Manicaland Province of Zimbabwe.
BACKGROUND: Patterns of person-to-person contacts relevant for infectious diseases transmission are still poorly quantified in Sub-Saharan Africa (SSA), where socio-demographic structures and behavioral attitudes are expected to be different from those of more developed countries. METHODS AND FINDINGS: We conducted a diary-based survey on daily contacts and time-use of individuals of different ages in one rural and one peri-urban site of Manicaland, Zimbabwe. A total of 2,490 diaries were collected and used to derive age-structured contact matrices, to analyze time spent by individuals in different settings, and to identify the key determinants of individuals' mixing patterns. Overall 10.8 contacts per person/day were reported, with a significant difference between the peri-urban and the rural site (11.6 versus 10.2). A strong age-assortativeness characterized contacts of school-aged children, whereas the high proportion of extended families and the young population age-structure led to a significant intergenerational mixing at older ages. Individuals spent on average 67% of daytime at home, 2% at work, and 9% at school. Active participation in school and work resulted the key drivers of the number of contacts and, similarly, household size, class size, and time spent at work influenced the number of home, school, and work contacts, respectively. We found that the heterogeneous nature of home contacts is critical for an epidemic transmission chain. In particular, our results suggest that, during the initial phase of an epidemic, about 50% of infections are expected to occur among individuals younger than 12 years and less than 20% among individuals older than 35 years. CONCLUSIONS: With the current work, we have gathered data and information on the ways through which individuals in SSA interact, and on the factors that mostly facilitate this interaction. Monitoring these processes is critical to realistically predict the effects of interventions on infectious diseases dynamics
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