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Exploring the potential of timetable fragility across multiple delay-related objectives
No full textWhen looking at preventive actions for disturbance management, the focus is on designing robust timetables able to absorb secondary delays. Several approaches based on different robustness measures have been proposed in the last years. However, many of them consider predictions of knock-on delays without factoring in possible dispatching decisions, greatly reducing their validity in real-life settings. Given a timetable and suitable objective functions, the fragility concept is able to identify the train-resource pairs where a primary delay is more likely to generate large knock-on delays. In particular, the objective function should reflect real-time decision-making criteria adopted by dispatchers. Since no single, universally accepted measure exists, we explore some of the most common objective functions. Considering real-world data from a busy railway line in Norway, we propose additional analyzes, including exploring the impact of precedence constraints in optimal dispatching
Leveraging Big Data and Open Data “From” and “For” Open Innovation: Expanding the New Digital Frontier
No full textThe ongoing megatrend of digitalization has transformed how organizations innovate with their stakeholders, building on the prevalence of Big Data (BD), Open Data (OD), and Open Innovation (OI). Since the involvement of external actors is a common feature across these three phenomena, this special issue gathered contributions to understand their interplay and dynamics. Indeed, data are a valuable source for organizational innovation capacity, value creation, and value capture, representing possible inputs for OI. At the same time, OI practices, which emphasize knowledge exchange beyond organizational boundaries, also serve as mechanisms through which data can be acquired, generated, shared, and refined. In this sense, BD and OD can also originate from OI, as outputs of collaborative innovation processes in data-rich ecosystems. This bidirectional relationship between data and open and collaborative innovation demonstrates a new digital frontier for innovation activities. Yet, the current literature has only recently started to make sense of the distinctiveness of the new data-driven and data-enabled OI landscape. The individual studies published in the special issue adopt diverse methodologies and settings towards filling this gap. In this editorial, in addition to summarizing the special issue contributions, we develop a conceptual framework of “Open Innovation and the Convergence of Big and Open Data”, highlighting how the joint and contingent implementation of BD/OD and OI can lead to new and expended innovation outcomes and opportunities. The editorial concludes by outlining future research directions, calling for more empirical work across varied organizational contexts to deepen understanding of this intersection and guide managerial practice in leveraging BD/OD and OI in a mutually reinforcing manner
Semivariance, semicovariance matrix and lower partial moments for portfolio selection: Analytical and numerical results
No full textThe traditional quantitative risk measure in portfolio selection is the variance of the portfolio returns, a concept introduced by Harry Markowitz in his seminal work on Modern Portfolio Theory. However, variance penalizes both upside and downside deviations, which may not align with investor preferences, as the upside risk is generally desirable. Markowitz himself suggested focusing on downside risk, leading to the concept of semivariance, which only measures deviations below a certain threshold, typically the mean or a target return. Unlike variance, semivariance better captures investors’ aversion to losses. Despite its intuitive appeal, semivariance has been considered analytically intractable and numerically challenging, prompting scholars to explore various approximations over the years. In this paper, we show that optimization problems involving the semivariance or the more general Lower Partial Moments can be addressed as standard convex programs, with computational complexity comparable to the Mean-Variance framework. This breakthrough simplifies the use of downside risk measures, making them viable for both academic research and real-world applications
The Measurement of the Impact Time to Evaluate the Plate Thickness
No full textThe present study proposes a simple and low-cost indirect method for estimating the
thickness of plates by measuring the contact time (TC) generated by the impact of a freefalling
sphere. The theoretical model has been developed on Tsai approximation of Zener’s
theory, which describes the dynamic interaction between the sphere and the plate taking in
account the propagation of flexural waves. The methodology was validated through FEM
simulations and through an extensive experimental campaign, where the contact times were
measured using a simple electrical circuit. The results show excellent agreements between
predicted and actual thicknesses, with relative errors below 3% for λ < 1.5 (where λ is the
inelasticity parameter). For very thin plates and highly deformable materials, the above
accuracy decreases due to flexibility and plastic deformation. We believe the proposed
approach to be particularly promising in non-destructive testing applications within several
scenarios, where speed, cost-effectiveness, and safety are essential requirements
A deep X-ray look to the most obscured quasar at z~3.6 and its environment
No full textContext. The most luminous and obscured quasars (QSOs) detected through sensitive infrared all-sky surveys are thought to represent a key co-evolutionary phase from nuclear to circumgalactic (CG) scales in the formation of massive galaxies. In this context, hot dust obscured galaxies (hot DOGs) in the redshift interval z similar to 2 - 4 (the so-called cosmic noon) provide unique opportunities to investigate the relation between cosmic mass assembly and the nuclear accretion processes of luminous QSOs and galaxies at high-z. W0410-0913 (hereafter W0410-09) is a luminous (L-bol similar to 6.4 x 10(47) erg s(-1)) and obscured QSO at z = 3.631 that is characterized by a 30 kpc CG Ly alpha nebula (CGLAN), which is rather small when the similar to 100 kpc Ly alpha nebulae around the unobscured QSO is compared to the Type I QSO peers, and by an exceptional overdense environment of Ly alpha emitters (LAEs), with similar to 19 of them located in the CG region with a radius of 300 kpc at a distance of +/- 200 km s(-1) from the Hot DOG. Aims. Our aim is to detect and characterize active nuclear accretion in the Hot DOG W0410-09 and its environment. Methods. We carried out this study by exploiting a deep proprietary similar to 280 ks Chandra X-ray Observatory observation. We employed a set of empirical models suited for obscured sources and physically motivated spectroscopic models to account for a toroidal X-ray obscurer and the reprocessing of the X-ray radiation. Results. The source W0410-09 consistently exhibits nuclear obscuration levels from mild to high star formation; it is Compton-thick (CT) and has a hydrogen column density of N-H > 10(24) cm(-2) (and up to N-H similar to 10(25) cm(-2)) and an intrinsic luminosity of L2 - 10 > 10(45) erg s(-1). W0410-09 is therefore one of the most luminous and obscured QSO at z > 3.5 discovered so far. This level of obscuration and the highly accreting nature of the Hot DOGs suggest that W0410-09 is undergoing a blow-out phase. This phase is predicted by models of merger-driven QSO formation scenarios, where strong winds begin to clear the dusty obscuring medium from the nuclear surroundings. We speculate that this heavy nuclear obscuration limits the amount of UV disk emission that powers its CGLAN, which in turn likely explains its small nebula size. Except for W0410-09, we detected no X-ray emission from any of the 19 LAEs. We analyzed their combined emission in several bands and only found a significant signal at the 3 sigma level in the 6-7 keV rest-frame energy band. We interpret this as caused by the Fe K alpha line. This strongly suggests heavily obscured but so far undetected active galactic nuclei (AGN) emission in several LAEs. Considering W0410-09, we estimate an AGN fraction of f(AGN)(LAE) = 5(-4)(+12)%. This value can reach similar to 35% when we account for unresolved obscured AGN, as suggested by the detection of the Fe K alpha line. Conclusions. W0410-09 is powered by an intrinsically luminous CT quasar. Its high obscuration likely explains the limited extent of its CGLAN. Our analysis suggests that this object is in a crucial transitional blow-out phase, during which powerful QSO-driven outflows will sweep out the nuclear obscuration to pave the way for an unobscured bright quasar