2,566 research outputs found
Tax-benefit systems, income distribution and work incentives in the European Union
In this paper we study the impact of tax-benefit systems on income inequality and work incentivesacross the 27 Member States of the European Union (EU). Using EUROMOD, the EU-wide taxbenefitmicrosimulation model, we disentangle the role of taxes, benefits and social insurancecontributions in influencing country specific Gini coefficients and Marginal Effective Tax Rates.The extent to which tax-benefit systems contribute to income redistribution and provide work incentives at the intensive margin is found to vary considerably across the 27 Member States of the EU. Our results further highlight the presence of a trade-off between income redistribution and work incentives across EU-27 countries
On the mass of supernova progenitors: the role of the CC reaction
A precise knowledge of the masses of supernova progenitors is essential to
answer various questions of modern astrophysics, such as those related to the
dynamical and chemical evolution of Galaxies. In this paper we revise the upper
bound for the mass of the progenitors of CO white dwarfs (\mup) and the lower
bound for the mass of the progenitors of normal type II supernovae (\mups). In
particular, we present new stellar models with mass between 7 and 10 \msun,
discussing their final destiny and the impact of recent improvements in our
understanding of the low energy rate of the \c12c12 reaction.Comment: To be published on the proceedings of NIC 201
An increase in the 12C + 12C fusion rate from resonances at astrophysical energies
Carbon burning powers scenarios that influence the fate of stars, such as the late evolutionary stages of massive stars1 (exceeding eight solar masses) and superbursts from accreting neutron stars2,3. It proceeds through the 12C + 12C fusion reactions that produce an alpha particle and neon-20 or a proton and sodium-23 - that is, 12C(12C, α)20Ne and 12C(12C, p)23Na - at temperatures greater than 0.4 × 109 kelvin, corresponding to astrophysical energies exceeding a megaelectronvolt, at which such nuclear reactions are more likely to occur in stars. The cross-sections 4 for those carbon fusion reactions (probabilities that are required to calculate the rate of the reactions) have hitherto not been measured at the Gamow peaks4 below 2 megaelectronvolts because of exponential suppression arising from the Coulomb barrier. The reference rate 5 at temperatures below 1.2 × 109 kelvin relies on extrapolations that ignore the effects of possible low-lying resonances. Here we report the measurement of the 12C(12C, α 0,1)20Ne and 12C(12C, p0,1)23Na reaction rates (where the subscripts 0 and 1 stand for the ground and first excited states of 20Ne and 23Na, respectively) at centre-of-mass energies from 2.7 to 0.8 megaelectronvolts using the Trojan Horse method 6,7 and the deuteron in 14N. The cross-sections deduced exhibit several resonances that are responsible for very large increases of the reaction rate at relevant temperatures. In particular, around 5 × 108 kelvin, the reaction rate is boosted to more than 25 times larger than the reference value5. This finding may have implications such as lowering the temperatures and densities 8 required for the ignition of carbon burning in massive stars and decreasing the superburst ignition depth in accreting neutron stars to reconcile observations with theoretical models3
Advanced Techniques for Design and Manufacturing in Marine Engineering
Modern engineering design processes are driven by the extensive use of numerical
simulations, and naval architecture as well as ocean engineering are no exception. Structural
design or fluid dynamic performance evaluation can only be carried out by means of several
dedicated pieces of software. Classical naval design methodology can take advantage of
the integration of these pieces of software, giving rise to more robust design in terms of
shape, structural and hydrodynamic performances, and manufacturing processes.
This Special Issue (SI) on “Advanced Techniques for Design and Manufacturing in
Marine Engineering”, published in the Journal of Marine Science and Engineering, aimed to
invite researchers and engineers from both academia and industry to publish the latest
progress in design and manufacturing techniques in marine engineering as well as to debate
current issues and future perspectives in this research area.
After a rigorous peer review process we accepted 11 papers [1–11], covering a wide
range of topics related to the themes proposed in the Special Issue. In [1], machine-learningbased
algorithms are developed in order to enhance the real-time decision process of
an AUV sailing yacht. In [2], topology optimization techniques and laser powder bed
fusion manufacturing have been synergically adopted to redesign the bulb of sailing yachts,
leading to drag reduction and improving overall boat performance. In [3], the topic of
sail design is discussed by means of numerical fluid structure interaction methods and
a practical tool is proposed to support the analyst during the design process of a yacht
sail plan. The sail design process is also investigated in [4] but using different tools,
such as combining a velocity prediction program, RANS computations, and analytical
approaches. The problem of grid generation in a CFD model has been studied in [5], where
the authors propose, for the particular shape of a submarine, an automated procedure
based on Cartesian adaptive grids. The applicability of a CFD numerical technique to a
complex biphase fluid medium is the key point of [6], where the robustness of the method
is tested to simulate the ventilation phenomenon occurring in stepped hull planing motor
yachts. In [7], an analytical tool incorporating the main dimensional naval coefficients of a
sailing boat is adopted during the early design stage, with the additional aim of quickly
predicting the overall resistance of the hull. In [8], different pieces of sensor information
have been used by the authors to train an algorithm able to control water sample collection
in deep water. Computational methods have been used in [9] to determine the resistance
of ship fuel tanks when subjected to an increased internal pressure. In [10], a simulation
model has been used to design a platform able to compensate for the wave action on a
vessel, with particular attention to the shape optimization of the structure in order to reduce
the total weight. Finally, in [11], CFD tools using moving meshes have been adopted to
simulate turbulent flows that originate in an oscillating water column device and move a
Savonius turbine
E-grocery logistics: exploring the gap between research and practice
Purpose: This paper investigates the logistics management in the e-grocery sector. It contrasts the key issues faced by practitioners and the topics addressed in the academic literature, to identify potential misalignments between research and practice and propose avenues for future efforts. Design/methodology/approach: This work adopts a twofold methodological approach. From an academic perspective, a systematic literature review (SLR) is performed to define the topics addressed so far by scholars when analysing e-grocery logistics. From a managerial perspective, a Delphi study is accomplished to identify the most significant issues faced by logistics practitioners in the e-grocery context and the associated significance. Findings: The study develops a conceptual framework, identifying and mapping the 9 main logistics challenges for e-grocery along 4 clusters, in the light of a logistics-related revision of the SCOR model: distribution network design (area to be served, infrastructures), order fulfilment process (picking, order storage, consolidation, delivery), logistics-related choices from other domains (product range, stock-out management) and automation. These elements are discussed along three dimensions: criticalities, basic and advanced/automation-based solutions. Finally, the main gaps are identified – in terms of both under-investigated topics (order storage and stock-out management) and investigated topics needing further research (picking and automation) – and research questions and hypotheses are outlined. Originality/value: This paper provides a threefold contribution, revolving around the developed framework. First, it investigates the state of the art about e-grocery logistics, classifying the addressed themes. Second, it explores the main issues e-grocery introduces for logistics practitioners. Third, it contrasts the two outcomes, identifying the misalignment between research and practice, and accordingly, proposing research directions
Thermo-Mechanical Behaviour of Flax-Fibre Reinforced Epoxy Laminates for Industrial Applications
The present work describes the experimental mechanical characterisation of a natural flax fibre reinforced epoxy polymer composite. A commercial plain woven quasi-unidirectional flax fabric with spun-twisted yarns is employed in particular, as well as unidirectional composite panels manufactured with three techniques: hand-lay-up, vacuum bagging and resin infusion. The stiffness and strength behaviours are investigated under both monotonic and low-cycle fatigue loadings. The analysed material has, in particular, shown a typical bilinear behaviour under pure traction, with a knee yield point occurring at a rather low stress value, after which the material tensile stiffness is significantly reduced. In the present work, such a mechanism is investigated by a phenomenological approach, performing periodical loading/unloading cycles, and repeating tensile tests on previously \u201cyielded\u201d samples to assess the evolution of stiffness behaviour. Infrared thermography is also employed to measure the temperature of specimens during monotonic and cyclic loading. In the first case, the thermal signal is monitored to correlate departures from the thermoelastic behaviour with the onset of energy loss mechanisms. In the case of cyclic loading, the thermoelastic signal and the second harmonic component are both determined in order to investigate the extent of elastic behaviour of the materia
Big Bang nucleosynthesis revisited via Trojan Horse Method measurements
Nuclear reaction rates are among the most important input for understanding
the primordial nucleosynthesis and therefore for a quantitative description of
the early Universe. An up-to-date compilation of direct cross sections of
2H(d,p)3H, 2H(d,n)3He, 7Li(p,alpha)4He and 3He(d,p)4He reactions is given.
These are among the most uncertain cross sections used and input for Big Bang
nucleosynthesis calculations. Their measurements through the Trojan Horse
Method (THM) are also reviewed and compared with direct data. The reaction
rates and the corresponding recommended errors in this work were used as input
for primordial nucleosynthesis calculations to evaluate their impact on the 2H,
3,4He and 7Li primordial abundances, which are then compared with observations.Comment: 22 pages, 7 figures, accepted for publication in The Astrophysical
Journa
Combining crowdsourcing and mapping customer behaviour in last-mile deliveries
In the light of the dramatic rise of online sales, last-mile deliveries (i.e., the delivery of products ordered online to the final customer) have been increasingly gaining the attention of both managers and academics. As a matter of fact, they are very critical in terms of effectiveness (as customers demand fast and accurate deliveries), and efficiency (since they imply very high costs). Henceforth, logistics players operating in the B2C e-commerce environment are striving to find and implement innovative solutions, different from the costly traditional by-van home deliveries. Among the options analysed by scholars so far, two promising ones are crowdsourcing logistics (i.e., outsourcing delivery activities to “common” people) and mapping the behaviour of customers (i.e., analysing the probability distribution of the customer presence at home and accordingly scheduling deliveries to minimise the probability of failed deliveries). In this paper, we introduce and study a combination between the two solutions, proposing a variant of the Vehicle Routing Problem, which considers both the Availability Profiles and Occasional Drivers (VRPAPOD). We model the delivery problem as a mixed-integer program and solve it with a branch-and-price algorithm. To analyse the benefit of the combined use of crowdshipping and customers availability profiles (APs), we conduct several experiments in a real context in the city of Milan, randomly extracting 100 customers in a 16 km2 area. The combined solution is compared with two benchmarking models, namely the traditional home delivery (traditional VRP) and the crowdsourcing logistics option (Vehicle Routing Problem with Occasional Drivers (VRPOD)). Results prove that logistics players can achieve important benefits by relying on the crowd and scheduling deliveries according to clients' APs, which become more significant in case of high drivers availability
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