On positivity of parton distributions

We discuss the bounds on polarized parton distributions which follow from their definition in terms of cross section asymmetries. We spell out how the bounds obtained in the naive parton model can be derived within perturbative QCD at leading order when all quark and gluon distributions are defined in terms of suitable physical processes. We specify a convenient physical definition for the polarized and unpolarized gluon distributions in terms of Higgs production from gluon fusion. We show that these bounds are modified by subleading corrections, and we determine them up to NLO. We examine the ensuing phenomenological implications, in particular in view of the determination of the polarized gluon distribution.Comment: 20 pages, 8 figures included by epsf, plain tex with harvma

Orthogonal-Array based Design Methodology for Complex, Coupled Space Systems

The process of designing a complex system, formed by many elements and sub-elements interacting between each other, is usually completed at a system level and in the preliminary phases in two major steps: design-space exploration and optimization. In a classical approach, especially in a company environment, the two steps are usually performed together, by experts of the field inferring on major phenomena, making assumptions and doing some trial-and-error runs on the available mathematical models. To support designers and decision makers during the design phases of this kind of complex systems, and to enable early discovery of emergent behaviours arising from interactions between the various elements being designed, the authors implemented a parametric methodology for the design-space exploration and optimization. The parametric technique is based on the utilization of a particular type of matrix design of experiments, the orthogonal arrays. Through successive design iterations with orthogonal arrays, the optimal solution is reached with a reduced effort if compared to more computationally-intense techniques, providing sensitivity and robustness information. The paper describes the design methodology in detail providing an application example that is the design of a human mission to support a lunar base

A network approach to rank countries chasing sustainable development

In 2015, the United Nations established the Agenda 2030 for sustainable development, addressing the major challenges the world faces and introducing the 17 Sustainable Development Goals (SDGs). How are countries performing in their challenge toward sustainable development? We address this question by treating countries and Goals as a complex bipartite network. While network science has been used to unveil the interconnections among the Goals, it has been poorly exploited to rank countries for their achievements. In this work, we show that the network representation of the countries-SDGs relations as a bipartite system allows one to recover aggregate scores of countries’ capacity to cope with SDGs as the solutions of a network’s centrality exercise. While the Goals are all equally important by definition, interesting differences self-emerge when non-standard centrality metrics, borrowed from economic complexity, are adopted. Innovation and Climate Action stand as contrasting Goals to be accomplished, with countries facing the well-known trade-offs between economic and environmental issues even in addressing the Agenda. In conclusion, the complexity of countries’ paths toward sustainable development cannot be fully understood by resorting to a single, multipurpose ranking indicator, while multi-variable analyses shed new light on the present and future of sustainable development

Theoretical Analysis of Polarized Structure Functions

We review the analysis of polarized structure function data using perturbative QCD at next-to-leading order. We use the most recent experimental data to obtain updated results for polarized parton distributions, first moments and the strong coupling. We also discuss several theoretical issues involved in this analysis and in the interpretation of its results. Finally, we compare our results with other similar analyses in the recent literature

Are Parton Distributions Positive?

We show that the naive positivity conditions on polarized parton distributions which follow from their probabilistic interpretation in the naive parton model are reproduced in perturbative QCD at the leading log level if the quark and gluon distribution are defined in terms of physical processes. We show how these conditions are modified at the next-to-leading level, and discuss their phenomenological implications, in particular in view of the determination of the polarized gluon distributionComment: 5 pages, 4 figures, latex with espcrc2 and epsfi

SET, A SCENARIO EVALUATOR TOOL FOR SUPPORTING SPACE-EXPLORATION MISSION-ARCHITECTURE DESIGN

The design of space-exploration missions begins with a mission statement that defines the ultimate goals of the mission itself. The mission-architecture defines, instead, how the mission will work in practice, and encompasses all the elements that will take part in it. It includes such issues as the synergies of manned and robotic resources, mission control, and the mission timeline. The mission-architecture design activity is an iterative process in general aimed at the maximization of the cost effectiveness (or value) of the mission and minimization of costs. This is performed by successive comparisons and evaluation of the alternative generated mission architectures. The Scenario Evaluator Tool (SET) is conceived to support the engineering team in the framework of the space mission design process. In particular, SET is a simulation software tool that allows building mission architectures with a significant reduction of development time and computational effort. The software allows the characterization, the comparison, and optimization of exploration scenarios and building blocks through a user friendly graphical interface. Each mission-architecture is characterized and evaluated on the basis of the mass budget of the building blocks, cost index and exploration capabilities. SET is general enough to allow the design of several space exploration scenarios for Gap-analysis studies (flexibility). Further, it allows the users to introduce new model libraries (expandability). This paper describes the main features and the potentialities of the simulation software. To show the working principle of SET, a hypothetical human space-exploration mission scenario has been developed and implemented. The results has been accomplished in the framework of STEPS (Systems and Technologies for the ExPloration of Space), which is a research project co-financed by Piedmont Region (Italy), firms and universities of the Piedmont Aerospace District