1,721,056 research outputs found
Le costanti fondamentali e il Sistema Internazionale del prossimo millennio
No full textIn 2018 the General Conference on Weights and Measures reformed the International System of Units by adopting exact values for some fundamental constant of physics. The kilogram, the ampere, the kelvin and the mole, units defined in the past by material artefacts or physical properties of matter are today defined
and realized starting from the knowledge of the modern world
Irreversible relativistic thermodynamics: a dynamic approach
No full textA revisitation of a relativistic continuum Thermodynamics is
proposed. A material body is regarded as a
binary system, consisting of two interacting subsystems, respectively called the material substratum and the heat subsystem. A detailed analysis of the interactions, as well
as of the limitations posed by the second law of Thermodynamics is developed. The resulting scheme provides a description of heat conduction and of internal dissipation
consistent with the existence of a finite wave speed for both temperature and acceleration field
Sistemi di riferimento in Relativita` Generale
No full textThe theory of physical frames of reference in curved space-time is reviewed. The construction of a tensor analysis commuting with the spatial resolution process is discussed. A few applications are examined
Avogadro and Planck Constants, Two Pillars of the International System of Units
Full text linkThe International System of Units (SI), the current form of the metric system and the world’s most used system of units, has been continuously updated and refined since the Metre Convention of 1875 to ensure that it remains up to date with the latest scientific and technological advances. The General Conference on Weights and Measures, at its 26th meeting in 2018, decided to adopt stipulated values of seven physical constants linked to seven measurement units (the second, meter, kilogram, ampere, kelvin, mole, and candela). This paper reviews the technologies developed, in intense and long-standing work, to determine the Avogadro and Planck constants, which are now integral to realising the kilogram
Unità di misura e costanti fondamentali
No full textNel 2018 la Conferenza generale dei pesi e delle misure riformerà il Sistema Internazionale di unità di misura adottando valori convenzionali per alcune costanti fondamentali. Si completerà così il passaggio da unità definite tramite campioni materiali a unità dettate dai parametri liberi dei modelli teorici
Legendre transformation in mechanics: a gauge-theoretical approach
No full textA gauge-invariant formulation of the Legendre transformation in mechanics, extending toarbitrary non-autonomous systems the symplectic approach of W.M.Tulczyjew is presented
Floating rigid bodies: a note on the conservativeness of the hydrostatic effects
No full textWithin the framework of Lagrangian mechanics, the conservativeness of the hydrostatic forces acting on a floating rigid body is proved. The representation of the associated hydrostatic potential is explicitly worked out. The invariance of the resulting Lagrangian with respect to surge, sway and yaw motions is used in connection with the Routh procedure in order to convert the original dynamical problem into a reduced one, in three independent variables. This allows to put on rational grounds the study of hydrostatic equilibrium, introducing the concept of pseudo-stability, meant as stability with respect to the reduced problem. The small oscillations of the system around a pseudo-stable equilibrium configuration are discussed
A new geometrical framework for time-dependent Hamiltonian Mechanics
No full textThe gauge-theoretical approach to classical mechanics is applied to the study of time-dependent hamiltonian dynamics. The construction of the lagrangian and
hamiltonian bundles is revisited. A reformulation of the basic themes of hamiltonian mechanics in the newer scheme is discussed
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