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The direct, not V1-mediated, functional influence between the thalamus and middle temporal complex in the human brain is modulated by the speed of visual motion
No full textAbstract The main visual pathway that conveys motion information to the middle temporal complex (hMT+) originates from the primary visual cortex (V1), which, in turn, receives spatial and temporal features of the perceived stimuli from the lateral geniculate nucleus (LGN). In addition, visual motion information reaches hMT+ directly from the thalamus, bypassing the V1, through a direct pathway. We aimed at elucidating whether this direct route between {LGN} and hMT+ represents a ‘fast lane’ reserved to high-speed motion, as proposed previously, or it is merely involved in processing motion information irrespective of speeds. We evaluated functional magnetic resonance imaging (fMRI) responses elicited by moving visual stimuli and applied connectivity analyses to investigate the effect of motion speed on the causal influence between {LGN} and hMT+, independent of V1, using the Conditional Granger Causality (CGC) in the presence of slow and fast visual stimuli. Our results showed that at least part of the visual motion information from {LGN} reaches hMT+, bypassing V1, in response to both slow and fast motion speeds of the perceived stimuli. We also investigated whether motion speeds have different effects on the connections between {LGN} and functional subdivisions within hMT+: direct connections between {LGN} and MT-proper carry mainly slow motion information, while connections between {LGN} and {MST} carry mainly fast motion information. The existence of a parallel pathway that connects the {LGN} directly to hMT+ in response to both slow and fast speeds may explain why {MT} and {MST} can still respond in the presence of {V1} lesions
Labor Supply Distortion and Capital Accumulation when Public Pension Systems Differ in an Aging Economy
No full textIn the context of an aging economy, the question addressed in this paper is: since pension systems differ in the funding methods - pay-as-you-go (PAYG) or fully funded - and payment schemes - Beveridgean or Bismarckian - under which setting can a sustainable public pension system provide both intergenerational and intragenerational redistribution, reduce labour supply distortion, and lead to a higher physical capital accumulation? Considering a series of partial reforms within a PAYG pension system to deal with aging, the results of our analysis show that commonly used policy actions distort labor supply and depress the capital market, thus, reducing the tax base and deteriorating the growth of the economy. As a consequence, the PAYG pension system does not appear to be reformable from inside, and a (partial) transition to a funded system is necessary.Moreover, we show that, within a fully funded scheme, a transition from a pure Beveridgean system to a pure Bismarckian system substantially improves the labor supply incentives, while it tends to depress physical capital accumulation. Hence, a mix between Beveridge and Bismarck substantiates a good compromise to balance the trade-off between equity and efficienc
Semiautomatic detection of villi in confocal endoscopy for the evaluation of celiac disease
No full textCeliac Disease (CD) is an immune-mediated enteropathy, diagnosed in the clinical practice by intestinal biopsy and the concomitant presence of a positive celiac serology. Confocal Laser Endomicroscopy (CLE) allows skilled and trained experts to potentially perform in vivo virtual histology of small-bowel mucosa. In particular, it allows the qualitative evaluation of mucosa alteration such as a decrease in goblet cells density, presence of villous atrophy or crypt hypertrophy. We present a semi-automatic method for villi detection from confocal endoscopy images, whose appearance change in case of villous atrophy. Starting from a set of manual seeds, a first rough segmentation of the villi is obtained by means of mathematical morphology operations. A merge and split procedure is then performed, to ensure that each seed originates a different region in the final segmentation. A border refinement process is finally performed, evolving the shape of each region according to local gradient intensities. Mean and median Dice coefficients for 290 villi originating from 66 images when compared to manually obtained ground truth are 80.71 and 87.96 respectively
Differential Bisimulation for a Markovian Process Algebra
No full textFormal languages with semantics based on ordinary differential equations (ODEs) have emerged as a useful tool to reason about large-scale distributed systems. We present differential bisimulation, a behavioral equivalence developed as the ODE counterpart of bisimulations for languages with probabilistic or stochastic semantics. We study it in the context of a Markovian process algebra. Similarly to Markovian bisimulations yielding an aggregated Markov process in the sense of the theory of lumpability, differential bisimulation yields a partition of the ODEs underlying a process algebra term, whereby the sum of the ODE solutions of the same partition block is equal to the solution of a single (lumped) ODE. Differential bisimulation is defined in terms of two symmetries that can be verified only using syntactic checks. This enables the adaptation to a continuous-state semantics of proof techniques and algorithms for finite, discrete-state, labeled transition systems. For instance, we readily obtain a result of compositionality, and provide an efficient partition-refinement algorithm to compute the coarsest ODE aggregation of a model according to differential bisimulation
Experimental Analysis for Lubricant and Punch Selection in Shear Extrusion of Aa-6063
No full textShear extrusion is a forming process which is based on combined backward cup-forward rod extrusion. This extrusion process is attractive due its potential to achieve severe plastic deformation thus enabling texture and microstructural control of materials. Furthermore, the economic potential of shear extrusion for mass production and production of complex shapes provides for numerous applications in automotive, transportation, aero-space and other industries. However, a trending challenge in the use of this method for complex shapes is the design and selection of tools to achieve a high quality product. This paper focuses on deep study of shear extrusion of AA-6063. The process was studied experimentally using variables which affect the forming load as well as the quality of the product. It is concluded from the load-displacement and stress plots that a punch with large diameter and small punch land is desirable for easy forming of the material during shear extrusion. Analysis of the effect of lubricants on deformation load and stress shows that palm oil lubricant remains the best lubricant of the four lubricants examined since its gives the minimum load obtained during shear extrusion
Global Protocol Implementations via Attribute-Based Communication
No full textSeveral type systems have been developed to address the conformance between specifications and implementations, where types are specifications and type-checking ensures the conformance relation. In this paper, we take a different perspective and assume that programming takes place only at the specification level, by using a type language that captures protocols of interaction. Specifications provide the global interaction scheme and lay the basis for an automatic (provably correct) generation of implementations. The latter is obtained by a translation into a rich formalism that relies on attribute-based communication, whose expressiveness permits modeling in a natural way the symmetric link between message recipient and emitter
Probabilistic Forecasts of Bike-Sharing Systems for Journey Planning
No full textWe study the problem of making forecasts about the future availability of bicycles in stations of a bike-sharing system (BSS). This is relevant in order to make recommendations guaranteeing that the probability that a user will be able to make a journey is sufficiently high. To do this we use probabilistic predictions obtained from a queuing theoretical time-inhomogeneous model of a BSS. The model is parametrized and successfully validated using historical data from the Vélib' BSS of the City of Paris.
We develop a critique of the standard root-mean-square-error (RMSE), commonly adopted in the bike-sharing research as an index of the prediction accuracy, because it does not account for the stochasticity inherent in the real system. Instead we introduce a new metric based on scoring rules. We evaluate the average score of our model against classical predictors used in the literature. We show that these are outperformed by our model for prediction horizons of up to a few hours. We also discuss that, in general, measuring the current number of available bikes is only relevant for prediction horizons of up to few hours
A unified framework for differential aggregations in Markovian process algebra
No full textFluid semantics for Markovian process algebra have recently emerged as a computationally attractive approximate way of reasoning about the behaviour of stochastic models of large-scale systems. This interpretation is particularly convenient when sequential components characterised by small local state spaces are present in many independent copies. While the traditional Markovian interpretation causes state-space explosion, fluid semantics is independent from the multiplicities of the sequential components present in the model, just associating a single ordinary differential equation (ODE) with each local state. In this paper we analyse the case of a process algebra model inducing a large ODE system. Previous work, known as exact fluid lumpability, requires two symmetries: ODE aggregation is possible for processes that i) are isomorphic and that ii) are present with the same multiplicities. We first relax the latter requirement by introducing the notion of ordinary fluid lumpability, which yields an ODE system where the sum of the aggregated variables is preserved exactly. Then, we consider approximate variants of both notions of lumpability which make nearby processes symmetric after a perturbation of their parameters. We prove that small perturbations yield nearby differential trajectories. We carry out our study in the context of a process algebra that unifies two synchronisation semantics that are well studied in the literature, useful for the modelling of computer systems and chemical networks, respectively. In both cases, we provide numerical evidence which shows that, in practice, many heterogeneous processes can be aggregated with negligible errors
A Simple Effective Heuristic for Embedded Mixed-Integer Quadratic Programming
No full textIn this paper we propose a fast optimization
algorithm for approximately minimizing convex quadratic
functions over the intersection of affine and separable constraints
(i.e., the Cartesian product of possibly nonconvex
real sets). This problem class contains many NP-hard problems
such as mixed-integer quadratic programming. Our
heuristic is based on a variation of the alternating direction
method of multipliers (ADMM), an algorithm for solving
convex optimization problems. We discuss the favorable
computational aspects of our algorithm, which allow it to
run quickly even on very modest computational platforms
such as embedded processors. We give several examples
for which an approximate solution should be found very
quickly, such as management of a hybrid-electric vehicle
drivetrain. Our numerical experiments suggest that our
method is very effective in finding a feasible point with
small objective value; indeed, we see that in many cases,
it finds the global solution
On the Statics of the Dome of the Basilica of S. Maria Assunta in Carignano, Genoa
No full textThe paper deals with the dome of the Basilica of S. Maria Assunta in Carignano in Genoa, designed by Galeazzo Alessi and built in the sixteenth century, for which meridian cracking, rather common in masonry domes, requires the assessment of the dome. In order to set a general procedure for the assessment this structures, limit analysis approaches are here discussed and compared. On the basis of classic limit analysis, local (dome only) and global (dome-drum system) collapse mechanisms are considered considering the different behaviour of several structural elements (lantern, shells of the dome, drum, colonnade). A static (safe theorem) and a kinematic approach are applied to the structure by means of equilibrium limit conditions and kinematically admissible collapse mechanisms. Comparisons between the obtained results are carried out so as to: (i) discuss a general approach to the assessment of dome-drum systems based on both numerical tools and standard limit analyses approaches; (ii) provide a first glance in the assessment of the dome