A tight-binding model for MoS2_2 monolayers

We propose an accurate tight-binding parametrization for the band structure of MoS$_2$ monolayers near the main energy gap. We introduce a generic and straightforward derivation for the band energies equations that could be employed for other monolayer dichalcogenides. A parametrization that includes spin-orbit coupling is also provided. The proposed set of model parameters reproduce both the correct orbital compositions and location of valence and conductance band in comparison with ab initio calculations. The model gives a suitable starting point for realistic large-scale atomistic electronic transport calculations.Comment: 35 pages, 8 figure

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

Gold and Silver joining technologies in the Moche Tombs “Señor de Sipán” and “Señora de Cao jewelery

About 200 gold and silver funerary ornaments from the Moche tombs “Señor de Sipán” and “Señora de Cao” were analyzed to determine their metallurgic characteristics. Of particular interest was the question about the gold-silver joining process. To this aim, following methods were employed, all based on the use of X-rays: - energy dispersive X-ray fluorescence; - transmission of monoenergetic fluorescent X-rays; - radiography. At least three joining methods were possibly identified: - of gluing gold and silver sheets; - of brazing using a proper solder; - of using a mercury amalgam

From time-series to complex networks: Application to the cerebrovascular flow patterns in atrial fibrillation

A network-based approach is presented to investigate the cerebrovascular flow patterns during atrial fibrillation (AF) with respect to normal sinus rhythm (NSR). AF, the most common cardiac arrhythmia with faster and irregular beating, has been recently and independently associated with the increased risk of dementia. However, the underlying hemodynamic mechanisms relating the two pathologies remain mainly undetermined so far; thus the contribution of modeling and refined statistical tools is valuable. Pressure and flow rate temporal series in NSR and AF are here evaluated along representative cerebral sites (from carotid arteries to capillary brain circulation), exploiting reliable artificially built signals recently obtained from an in silico approach. The complex network analysis evidences, in a synthetic and original way, a dramatic signal variation towards the distal/capillary cerebral regions during AF, which has no counterpart in NSR conditions. At the large artery level, networks obtained from both AF and NSR hemodynamic signals exhibit elongated and chained features, which are typical of pseudo-periodic series. These aspects are almost completely lost towards the microcirculation during AF, where the networks are topologically more circular and present random-like characteristics. As a consequence, all the physiological phenomena at microcerebral level ruled by periodicity - such as regular perfusion, mean pressure per beat, and average nutrient supply at cellular level - can be strongly compromised, since the AF hemodynamic signals assume irregular behaviour and random-like features. Through a powerful approach which is complementary to the classical statistical tools, the present findings further strengthen the potential link between AF hemodynamic and cognitive decline.Comment: 12 pages, 10 figure

A Positive-Weight Next-to-Leading-Order Monte Carlo for Z Pair Hadroproduction

We present a first application of a previously published method for the computation of QCD processes that is accurate at next-to-leading order, and that can be interfaced consistently to standard shower Monte Carlo programs. We have considered Z pair production in hadron-hadron collisions, a process whose complexity is sufficient to test the general applicability of the method. We have interfaced our result to the HERWIG and PYTHIA shower Monte Carlo programs. Previous work on next-to-leading order corrections in a shower Monte Carlo (the MC@NLO program) may involve the generation of events with negative weights, that are avoided with the present method. We have compared our results with those obtained with MC@NLO, and found remarkable consistency. Our method can also be used as a standalone, alternative implementation of QCD corrections, with the advantage of positivity, improved convergence, and next-to-leading logarithmic accuracy in the region of small transverse momentum of the radiated parton.Comment: 33 pages, 10 figure

A methodology for system-of-systems design in support of the engineering team

Space missions have experienced a trend of increasing complexity in the last decades, resulting in the design of very complex systems formed by many elements and sub-elements working together to meet the requirements. In a classical approach, especially in a company environment, the two steps of design-space exploration and optimization are usually performed by experts inferring on major phenomena, making assumptions and doing some trial-and-error runs on the available mathematical models. This is done especially in the very early design phases where most of the costs are locked-in. With the objective of supporting the engineering team and the decision-makers during the design of complex systems, the authors developed a modelling framework for a particular category of complex, coupled space systems called System-of-Systems. Once modelled, the System-of-Systems is solved using a computationally cheap parametric methodology, named the mixed-hypercube approach, based on the utilization of a particular type of fractional factorial design-of-experiments, and analysis of the results via global sensitivity analysis and response surfaces. As an applicative example, a system-of-systems of a hypothetical human space exploration scenario for the support of a manned lunar base is presented. The results demonstrate that using the mixed-hypercube to sample the design space, an optimal solution is reached with a limited computational effort, providing support to the engineering team and decision makers thanks to sensitivity and robustness informa- tion. The analysis of the system-of-systems model that was implemented shows that the logistic support of a human outpost on the Moon for 15 years is still feasible with currently available launcher classes. The results presented in this paper have been obtained in cooperation with Thales Alenia Space—Italy, in the framework of a regional programme called STEP

Mean first passage times of processes driven by white shot noise

The systems driven by white shot noise are analyzed based on mean first passage times. The shot noise has exponentially distributed jump heights. The the linkage between the results and the steady state probability density function of the process are presented

Measuring economic water scarcity in agriculture: a cross-country empirical investigation

High water availability enhances agricultural performance and food security. However, many countries where water is abundant according to hydrological indicators face difficulties in the utilization of water in agriculture, being in a situation of economic water scarcity (EWS), due to lack of institutional and material means for water management and governance. EWS faces a stronger challenge of measurability, if compared to physical water scarcity. Since the Sustainable Development Goal Indicator on Integrated management of domestic and transboundary water resources (IWRM) is a unique attempt to quantify information on water management at a national level, we explore whether it can represent a valid metric for EWS measurement. We first show that a high level of water management is neither necessarily associated to high economic power of the country nor to low physical water availability. Then, we analyze whether the indicator can predict typical EWS situations such as low agricultural productivity and inefficient water use. Although the importance of water institutions for agriculture is well known through case studies at the local level, we make the first attempt to quantify the strengths of this relation at a global scale for different crops in climatic diverse countries. We detect a positive and significant association between IWRM level and yield, and consequently a negative and equally significant association between the IWRM level and the crop water footprint. Statistical significance holds also when potentially confounding variables are included in a multiple regression analysis. We infer from this analysis that good water management, as detectable through the IWRM indicator, improves land productivity and water saving, in turn mitigating EWS. Our findings pave the way toward the use of the IWRM indicator as a valuable tool for measuring EWS in agriculture, bridging the measurability gap of economic water scarcity, with straightforward policy implications in favour of investments in water management as a lever for enhancing food security and development

Bottom Production

We review the prospects for bottom production physics at the LHC.Comment: 74 pages, Latex, 71 figures, to appear in the Report of the ``1999 CERN Workshop on SM physics (and more) at the LHC'', P. Nason, G. Ridolfi, O. Schneider G.F. Tartarelli, P. Vikas (conveners