888 research outputs found
The Development of Deep and Short Sea Shipping Container Routes Departing from Italian Ports
In this paper, an analysis of the development of Deep Sea Shipping (DSS) and Short Sea Shipping (SSS) container routes calling at Italian ports, is carried out. Data about DSS routes have been collected in the years: 2011, 2014, 2018 and 2019, while data about SSS services have been collected in 2010 and 2018. Italian ports have been classified as follows: Ligurian multi-port gateway cluster, which is formed by Leghorn, La Spezia, Genoa, Savona/Vado Ligure; Northern Adriatic multi-port gateway cluster, made up of Ancona, Ravenna, Venice and Trieste; Campanian multi-port gateway cluster, composed of Naples and Salerno; hub ports, i.e. Gioia Tauro, Cagliari (only until 2018) and Taranto (only until 2014). The most important gateway cluster, for both DSS and SSS services, is the Ligurian one which includes Genoa which is by far the major Italian container gateway port. Genoa has shown an almost constant increase in container traffic in the time period analyzed. Italian hub ports are also an important group, but they have registered a negative trend in the years under analysis. DSS routes, to Far East and the American Continent, usually call at the Ligurian ports and the hub port of Gioia Tauro. Northern Adriatic ports are crossed by only a few DSS routes, but they are crossed by a large number of SSS routes, especially feeder ones, with transshipment mainly in the hub ports of Gioia Tauro, Marsaxlokk, Piraeus and Port Said. The evolution of DSS services shows clearly the effects of naval gigantism phenomenon: the number of DSS services has decreased, but the total and, especially, the average DWT have increased. As regards SSS routes, also their frequencies have decreased, but their length and, in particular, the number of ports called, have increased: this choice is performed by container operators in order to increase the ships ’load factor’
A Review on Fractional Differential Equations and a Numerical Method to Solve Some Boundary Value Problems
Fractional differential equations can describe the dynamics of several complex and nonlocal systems with memory. They arise in many scientific and engineering areas such as physics, chemistry, biology, biophysics, economics, control theory, signal and image processing, etc. Particularly, nonlinear systems describing different phenomena can be modeled with fractional derivatives. Chaotic behavior has also been reported in some fractional models. There exist theoretical results related to existence and uniqueness of solutions to initial and boundary value problems with fractional differential equations; for the nonlinear case, there are still few of them. In this work we will present a summary of the different definitions of fractional derivatives and show models where they appear, including simple nonlinear systems with chaos. Existing results on the solvability of classical fractional differential equations and numerical approaches are summarized. Finally, we propose a numerical scheme to approximate the solution to linear fractional initial value problems and boundary value problems
What a Difference a Disaster Makes: The Telehealth Revolution in the Age of COVID-19 Pandemic
Learning to predict target location with turbulent odor plumes
: Animal behavior and neural recordings show that the brain is able to measure both the intensity and the timing of odor encounters. However, whether intensity or timing of odor detections is more informative for olfactory-driven behavior is not understood. To tackle this question, we consider the problem of locating a target using the odor it releases. We ask whether the position of a target is best predicted by measures of timing vs intensity of its odor, sampled for a short period of time. To answer this question, we feed data from accurate numerical simulations of odor transport to machine learning algorithms that learn how to connect odor to target location. We find that both intensity and timing can separately predict target location even from a distance of several meters; however, their efficacy varies with the dilution of the odor in space. Thus, organisms that use olfaction from different ranges may have to switch among different modalities. This has implications on how the brain should represent odors as the target is approached. We demonstrate simple strategies to improve accuracy and robustness of the prediction by modifying odor sampling and appropriately combining distinct measures together. To test the predictions, animal behavior and odor representation should be monitored as the animal moves relative to the target, or in virtual conditions that mimic concentrated vs dilute environments
Curvature invariants of static spherically symmetric geometries
We construct all independent local scalar monomials in the Riemann tensor at
arbitrary dimension, for the special regime of static, spherically symmetric
geometries. Compared to general spaces, their number is significantly reduced:
the extreme example is the collapse of all invariants ~ Weyl^k, to a single
term at each k. The latter is equivalent to the Lovelock invariant L_k.
Depopulation is less extreme for invariants involving rising numbers of Ricci
tensors, and also depends on the dimension. The corresponding local
gravitational actions and their solution spaces are discussed.Comment: 14 page
Phase transitions, double-scaling limit, and topological strings
Topological strings on Calabi--Yau manifolds are known to undergo phase
transitions at small distances. We study this issue in the case of perturbative
topological strings on local Calabi--Yau threefolds given by a bundle over a
two-sphere. This theory can be regarded as a q--deformation of Hurwitz theory,
and it has a conjectural nonperturbative description in terms of q--deformed 2d
Yang--Mills theory. We solve the planar model and find a phase transition at
small radius in the universality class of 2d gravity. We give strong evidence
that there is a double--scaled theory at the critical point whose all genus
free energy is governed by the Painlev\'e I equation. We compare the critical
behavior of the perturbative theory to the critical behavior of its
nonperturbative description, which belongs to the universality class of 2d
supergravity. We also give evidence for a new open/closed duality relating
these Calabi--Yau backgrounds to open strings with framing.Comment: 49 pages, 3 eps figures; section added on non-perturbative proposal
and 2d gravity; minor typos correcte
Dati preliminari di abbondanza e distribuzione di Salmo fibreni Zerunian & Gandolfi 1990 nel bacino di Posta Fibreno (Italia Centrale): primo utilizzo del visual census
Preliminary abundance and distribution data of Salmo fibreni Zerunian & Gandolfi 1990 in the Posta Fibreno basin (Central Italy): first use of visual census - Lake Posta Fibreno and Stream Dova harbour Salmo fibreni Zerunian & Gandolfi 1990, an endemic taxon still quite unknown in its phenology and ecology. We report here a first attempt to quantitatively estimate the abundance of the lacustrine population of S. fibreni by means of the visual census method, generally considered as a non-intrusive technique and capable of providing ecological information otherwise not achievable. A total of 19 observations (snorkelling and scuba diving) during 1 year (September 2006-July 2007) in the lake zones presently frequented by S. fibreni were performed along transects of 100-130 m length by two observers. Densities of S. fibreni resulted to be negatively affected by light (1 single diurnal contact) and very low everywhere in the lake (mean 2 ind per 100 m, max 9 ind per 100 m), especially if compared to Rio Dova densities as derived from electrofishing. The distribution of S. fibreni within the basin seems to be strictly dependent on substrate composition, springs proximity, presence of flourishing aquatic vegetation. Immediate measures of conservation and support appear to be necessary, as the species individual numbers clearly point out a high risk of extinction
Black Hole Radiation (with and) without Weyl Anomaly
In the semiclassical analysis of black hole radiation in matter-coupled
dilaton gravity, a one-parameter ``"-family of measures for the path
integral quantization of the matter fields is considered. The Weyl anomaly is
proportional to the parameter , but the black hole radiation seen by
minkowskian observers at future null infinity is -independent.Comment: 13 pages, LaTex. [Typographical error in Eq.(36) was corrected.
Comments on the relation between our 2D-gravity results and some known
results on the chiral Schwinger model were added. Two references were added.
Fermi-Walker gauge in 2+1 dimensional gravity.
It is shown that the Fermi-Walker gauge allows the general solution of
determining the metric given the sources, in terms of simple quadratures. We
treat the general stationary problem providing explicit solving formulas for
the metric and explicit support conditions for the energy momentum tensor. The
same type of solution is obtained for the time dependent problem with circular
symmetry. In both cases the solutions are classified in terms of the invariants
of the Wilson loops outside the sources. The Fermi-Walker gauge, due to its
physical nature, allows to exploit the weak energy condition and in this
connection it is proved that, both for open and closed universes with
rotational invariance, the energy condition imply the total absence of closed
time like curves. The extension of this theorem to the general stationary
problem, in absence of rotational symmetry is considered. At present such
extension is subject to some assumptions on the behavior of the determinant of
the dreibein in this gauge. PACS number: 0420Comment: 28 pages, RevTex, no figure
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