823 research outputs found
Some remarks on the use of constraints as controls in rational mechanics.
No full textThe author considers a mechanical system with generalized coordinates = (q,u), with positive definite kinetic energy as usual. However, when the coordinates
are considered as controls, under convenient assumptions, the q-subsystem is governed by
the same Euler-Lagrange equations, as developed by Bressan and Rampazzo in previous papers.
Moreover, due to the presence of the derivative
du/dt of the control in the ODEs for q (and the corresponding momentum p), one does not
have an ordinary control system. According to the author, “in a optimal control problem one has to expect an impulsive behaviour
of its trajectories. . . in this paper we investigate the existence of Lagrangian coordinates for
which the solutions (q, p)(·) of the corresponding control system are independent of the way of
bridging the discontinuities of the control
u(.)”
Energy of the harmonics in a vibrating string after the impact of a hammer
No full textThe author studies the oscillatory motion of a string after an impact with a rigid hammer. The schematization of the impact that is proposed here differs from the other schematization only in the initial conditions. By means of Fourier analysis the author calculates the amplitude, and thus the energy, of the harmonic modes that form the motion of the string. The ratios between the energies of these harmonic modes determine the timbre of the sound emitted by the string
Development and validation of a real-time TaqMan PCR assay for the detection of betanodavirus in clinical specimens
No full textDevelopment and validation of a real-time TaqMan PCR assay for the detection of betanodavirus in clinical specimens
Panzarin V, Patarnello P, Mori A, Rampazzo E, Cappellozza E, Bovo G, Cattoli G.
Betanodaviruses are the causal agents of viral encephalo-retinopathy, an infectious disease affecting more than 40 marine fish species, characterized by high morbidity and mortality. Because of its severe impact, robust diagnostic tools are required. The aim of this work was to develop and validate a real-time TaqMan PCR assay to detect betanodaviruses in clinical specimens by amplifying a conserved region of the RNA2 strand. The method proved to be specific and sensitive, being capable of detecting as low as 10 TCID(50)/ml. For clinical validation, samples from 100 marine fish were collected during a natural outbreak of disease and tested by three distinct laboratory methods, namely real-time TaqMan PCR, RT-seminested PCR and virus isolation. The results indicated optimal agreement between tests. The assay that was developed is capable of detecting members of all of the betanodavirus genetic groups currently described and can be considered a valid alternative to the time-consuming and contamination-prone nested PCR
Authigenic iron sulphides in recent sediments of the Venice Lagoon (northern Italy)
No full textThe data indicate early formation of microcrystalline pyrite, in both the framboids and the grains which are disseminated in the organic matter; it is frequently surrounded by massive pyrite growths and/or mixed Fe sulphides. Authigenic Fe sulphide formation in recent sediments (10-30 years old) in the Venice Lagoon is due to the anoxic conditions which seasonally affect the surface sediments and lead to interactions between reactive iron in solution and H2S. Iron may also be solubilized in a reducing environment from ferric hydroxides adsorbed on clays, from organo-metallic complexes, or directly by reduction of clastic grains of Fe oxides and hydroxides; H2S is produced in the same environment by bacterial reduction of sulfates in the pore-water. -from Author
Measurement of atmospheric deposition of polychlorinated dibenzo-p- dioxin and dibenzofurans in the Lagoon of Venice, Italy.
No full textData on atmospheric fall-out of polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) were
provided by collecting bulk deposition in four stations inside the Lagoon of Venice. A total of 44 monthly samples was
collected during the period July 1998–July 1999 in one site near an industrial area (Porto Marghera), one site in the city
of Venice, and two sites in the southern- and northernmost ends of the Lagoon. Fluxes of PCDD/Fs were between 0.1
and 470 pg m-2 d-1 , corresponding to 0–9.2 pg of 2,3,7,8-TCDD equivalents (TEQ) m-2 d-1 , with a gradient increasing
from remote to urban/industrial stations. Thus, annual deposition of PCDD/Fs to the Lagoon (total area ¼ 550 km 2 ),
calculated with various methods, turned out to be ~12 g, corresponding to ~400 mg TEQ. Significant differences were
found among the stations, with a clear fingerprinting signature (PCDF/PCDD > 1) of the deposition collected near
Porto Marghera, and a reversed pattern (PCDF/PCDD < 1) in the rest of the Lagoon, which pattern was similar to the
sediments collected in the same locations. Lastly, the amount of bulk PTEQ of all stations was compared with the
guide values for dioxins in depositions proposed by De Fré et al. [Organohalogen Compounds 45 (2000) 324]
Sulphide speciation in surface sediments of the Lagoon of Venice: a geochemical and minerographic study
No full textAlle origini della "limitatio" : tracce di suddivisioni agrarie in Etruria
No full textL’analisi della documentazione aerofotografica e quella relativa agli interventi sul terreno (ricognizioni di superficie e scavi archeologici) hanno consentito di ricostruire alcuni reticoli di suddivisione poderale di periodo etrusco, in particolare in Etruria Padana. Ciò ha permesso di identificare le peculiarità di questa operazione, sottolineandone le differenze con il sistema, ben più esteso, della centuriazione romana. I sistemi individuati nel territorio modenese sono stati messi in relazione allo sviluppo dell’insediamento rurale fra il VI ed il V sec. a. C. In conclusione del lavoro, ritengo si possa meglio intendere quanto affermato dagli agrimensori romani che esplicitamente pongono la dottrina agrimensoria romana sulla scia di una precedente tradizione di limitatio etrusca.The analysis of aerial photography and archaeological documentation (surveys and archaeological excavations) has allowed the reconstruction of some Etruscan field systems, particularly in Etruria Padana. This has made it possible to identify the main features of this method of land measurement, emphasizing the differences with the Roman land division. The field systems identified in Modena’s territory have been related to the development of rural settlements in the 6th and 5th century B. C. Finally I conclude the Roman Surveyors’ statement, which considers the Roman land division to be dependent on an earlier Etruscan Limitatio, can be better understood in light of this research
ON THE RIEMANNIAN STRUCTURE OF A LAGRANGIAN SYSTEM AND THE PROBLEM OF ADDING TIME-DEPENDENT CONSTRAINTS AS CONTROLS
No full textWe consider a Lagrangian system SIGMA with some additional time-dependent constraints, which are kinematically represented by functions of time which take values in a foliation F of the configuration manifold M. It is shown that the evolution of SIGMA depends continuously on these constraints (with respect to the C0 or weaker topologies) if and only if F satisfies certain orthogonality conditions. Some examples concerning a constrained particle and a rigid body are provided
Faithful representations for convex Hamilton-Jacobi equations
No full textWhen a Hamiltonian H = H(t, x, p) is convex in the adjoint variable p, the corresponding Hamilton - Jacobi equation
(0.1) u(t) + H(t, x, u(x)) = 0
is known to be the Bellman equation of a suitable optimal control problem. Of course, the latter is not unique, so it is interesting to select a good optimal control problem among those representing ( 0.1). We call such a representation faithful if (i) it involves a dynamics which is locally Lipschitz continuous in the state variable - so that a unique trajectory corresponds to any given control and initial point - and (ii) the Lagrangian displays the same regularity as H in the x variable. The main result of the present paper establishes the existence of faithful representations for a large class of Hamiltonians, including those for which the standard comparison theorems ( of viscosity solution theory) are valid. Moreover, our investigation includes t-measurable Hamiltonians as well.
If a faithful control-theoretical representation does exist ( and ( 0.1) enjoys uniqueness properties), one can infer sharp regularity results for the solution of ( 0.1) just by studying the regularity of the value function of the associated optimal control problem. A further application consists of a simple interpretation of the front propagation phenomenon in terms of optimal trajectories of the underlying minimum problem
CÆLUM ET TERRA: an INTERNET access addressed to the historical heritage preservation of the Osservatorio Astronomico di Brera and to modern astronomical knowledge dissemination
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