5,079 research outputs found
A new nonlocal nonlinear diffusion equation for image denoising and data analysis
In this paper we introduce and study a new feature-preserving nonlinear
anisotropic diffusion for denoising signals. The proposed partial differential
equation is based on a novel diffusivity coefficient that uses a nonlocal
automatically detected parameter related to the local bounded variation and the
local oscillating pattern of the noisy input signal. We provide a mathematical
analysis of the existence of the solution of our nonlinear and nonlocal
diffusion equation in the two dimensional case (images processing). Finally, we
propose a numerical scheme with some numerical experiments which demonstrate
the effectiveness of the new method
Manganese-containing mixed oxide electrodes as anode materials for degradation of model organic pollutants
Mixed oxide thin film electrodes have been prepared by thermal decomposition from alcoholic solution on Pt substrate. In particular, three different anodes have been obtained by co-deposition of Ru (Ruthenium) and Mn (Manganese) oxides, Ru, Mn and Cu (Copper) oxides and co-deposition of Ru, Mn and Co (Cobalt) oxides. The electrochemical behaviour of the prepared electrodes was evaluated by potentiodynamic polarization curves and cyclic voltammetry tests. We also tested and compared their oxidizing ability in the degradation of aqueous solutions containing methyl orange as model compound and small amount of chloride. Galvanostatic experiments were conducted in a membrane-free reactor. The treatment extent was assessed by detection of color and TOC decay. The electrogeneration of active chlorine, chlorate and perchlorate was also monitored. The preliminary results show that ternary oxides coated electrodes exhibit enhanced electrocatalytic activity without producing undesired chlorinated by-products
The determination of velocity fluctuations in shear flows by means of PTV
The present study considers the effects of some parameters in image acquisition and analysis procedures in connection with the use of the Particle Tracking Velocimetry (PTV) technique. The interest is focused towards flow fields with large velocity gradients as shear flows; in the paper, velocity measurements by PTV are performed in a turbulent channel flow upstream and downstream of a backward facing step at low Reynolds numbers. This is a flow field largely investigated in the past with available numerical and experimental to make comparison with. Among the possible parameters to be chosen in particle image acquisition and analysis, the following are considered
- the concentration of seeding particles in the imaged region;
- the spatial resolution of the image acquisition system;
- the parameters used in the image analysis algorithm
Nondegenerate abnormality, controllability, and gap phenomena in optimal control with state constraints
In optimal control theory, infimum gap means that there is a gap between the
infimum values of a given minimum problem and an extended problem, obtained by
enlarging the set of original solutions and controls. The gap phenomenon is
somewhat "dual" to the problem of the controllability of the original control
system to an extended solution. In this paper we present sufficient conditions
for the absence of an infimum gap and for controllability for a wide class of
optimal control problems subject to endpoint and state constraints. These
conditions are based on a nondegenerate version of the nonsmooth constrained
maximum principle, expressed in terms of subdifferentials. In particular, under
some new constraint qualification conditions, we prove that: (i) if an extended
minimizer is a nondegenerate normal extremal, then no gap shows up; (ii) given
an extended solution verifying the constraints, either it is a nondegenerate
abnormal extremal, or the original system is controllable to it. An application
to the impulsive extension of a free end-time, non-convex optimization problem
with control-polynomial dynamics illustrates the results
No Infimum Gap and Normality in Optimal Impulsive Control Under State Constraints
In this paper we consider an impulsive extension of an optimal control problem with unbounded controls, subject to endpoint and state constraints. We show that the existence of an extended-sense minimizer that is a normal extremal for a constrained Maximum Principle ensures that there is no gap between the infima of the original problem and of its extension. Furthermore, we translate such relation into verifiable sufficient conditions for normality in the form of constraint and endpoint qualifications. Links between existence of an infimum gap and normality in impulsive control have previously been explored for problems without state constraints. This paper establishes such links in the presence of state constraints and of an additional ordinary control, for locally Lipschitz continuous data
Impulsive optimal control problems with time delays in the drift term
We introduce a notion of bounded variation solution for a new class of
nonlinear control systems with ordinary and impulsive controls, in which the
drift function depends not only on the state, but also on its past history,
through a finite number of time delays. After proving the well posedness of
such solutions and the continuity of the corresponding input output map with
respect to suitable topologies, we establish necessary optimality conditions
for an associated optimal control problem. The approach, which involves
approximating the problem by a non impulsive optimal control problem with time
delays and using Ekeland principle combined with a recent, nonsmooth version of
the Maximum Principle for conventional delayed systems, allows us to deal with
mild regularity assumptions and a general endpoint constraint
Differential neural dynamics underling pragmatic and semantic affordance processing in macaque ventral premotor cortex
Premotor neurons play a fundamental role in transforming physical properties of observed objects, such as size and shape, into motor plans for grasping them, hence contributing to "pragmatic" affordance processing. Premotor neurons can also contribute to "semantic" affordance processing, as they can discharge differently even to pragmatically identical objects depending on their behavioural relevance for the observer (i.e. edible or inedible objects). Here, we compared the response of monkey ventral premotor area F5 neurons tested during pragmatic (PT) or semantic (ST) visuomotor tasks. Object presentation responses in ST showed shorter latency and lower object selectivity than in PT. Furthermore, we found a difference between a transient representation of semantic affordances and a sustained representation of pragmatic affordances at both the single neuron and population level. Indeed, responses in ST returned to baseline within 0.5 s whereas in PT they showed the typical sustained visual-to-motor activity during Go trials. In contrast, during No-go trials, the time course of pragmatic and semantic information processing was similar. These findings suggest that premotor cortex generates different dynamics depending on pragmatic and semantic information provided by the context in which the to-be-grasped object is presented
non native and hybrid in a changing environment conservation perspectives for the last italian red legged partridge alectoris rufa population with long natural history
Abstract The ever-increasing biotic homogenization - especially when associated with introgressive hybridization - raises concern for the reduction of spatial component of diversity in wildlife worldwide. Nonetheless, there is a growing attention to the potential conservation value of hybridization in fastening the adaptive evolutionary responses to rapidly changing selective pressures. Under these premises, we investigated the genetic affinity of the red-legged partridge (Alectoris rufa) population inhabiting Elba Island (Italy) in the context of the overall species phylogeography and particularly to the nominate subspecies it is traditionally ascribed to. Although notoriously hybrid with the congeneric A. chukar, this island population is of undisputedly value because of its long natural history and self-sustainability. As such, its adaptive conservation management calls for a comprehensive knowledge including the assessment of its geographic origin. For this purpose, 110 fecal samples were collected across Elba, genotyped at their joint Cytochrome-b and Control Region genes (2,249 characters), and compared with 149 conspecifics from all over the species distribution range. We confirmed a widespread A. chukar mitochondrial DNA introgression in Elba partridges, whereas their expected formal assignation to the nominate subspecies found in Italy and France was rejected, since these turned out to be closely related to conspecifics from the Iberian Peninsula. This counterintuitive result found support in a large variety of literary sources and compelling evidences from personal testimonies revealing recent intense management with farm-reared birds of Spanish origin. Although the nativeness of Elba partridges was disproved, we advise local authorities to keep warranting the ongoing conservation efforts - and especially restore the connectivity between the western and eastern island sub-populations - as this resource may still be conceived as the ultimate repository for part of the otherwise extinct Italian A. r. rufa genome. Indeed, the admixture with conspecifics from the Iberian Peninsula does not necessarily mean that the entirety of the native nuclear genome of Elba partridges has been wiped out. Furthermore, these latter represent an interesting case study in conservation biology to investigate the possible role played by introgressive hybridization in the adaptation to recent land use and vegetation cover changes associated with rural abandonment in an insular yet heavily anthropized context
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