1,720,983 research outputs found
A spasso con Feynman per le scintillanti strade dell'elettromagnetismo classico
No full textL’originale e poliedrico approccio di Richard P. Feynman all’elettro- magnetismo classico viene qui presentato nella sua generalita`, ripercorrendo l’in- tero percorso storico, dalla iniziale “teoria dell’assorbitore” all’approccio origina- le e poco noto delineato in appunti manoscritti del 1963 e sviluppato poi nelle Hughes Lectures del 1967-68. Alcune considerazioni che emergono da tale ap- proccio, particolarmente stimolanti, riguardo il pensiero di Feynman sulla natura dell’elettromagnetismo e, piu` in generale, delle interazioni fondamentali, vengono inoltre offerte al lettore interessato
Spin-orbit coupled Bose-Einstein condensates in a double well
Full text linkWe study the quantum dynamics of spin-orbit (SO) coupled Bose-Einstein condensates (BECs) in a double-well potential inspired by the recent experiment developed by NIST group. We focus on the regime where the number of atoms is very large and perform a two-mode approximation. An analytical solution of the two-site Bose-Hubbard-like Hamiltonian is found for weak nonlinear interactions by a rotating wave approximation (RWA). The quantum dynamics of several observables, ranging from the population and pseudospin imbalance, to the atomic and spin current are explicitly computed. We show a spin Josephson effect which could be detected in experiments and employed in realistic devices
L’approccio inedito di Feynman all’elettromagnetismo
No full textViene descritta una formulazione alternativa, mai pubblicata, dell’elettromagnetismo classico dovuta a Richard P. Feynman. Tale approccio è delineato e iniziato in alcuni appunti manoscritti, recentemente rinvenuti da M. A. Gottlieb negli archivi del Caltech, e successivamente completata da Feynman in altri contributi inediti. Partendo dal solo principio di relatività e da poche altre assunzioni fondamentali, Feynman riesce a derivare l’espressione della forza di Lorentz e le equazioni di Maxwell omogenee. Successivamente, con pochi ulteriori assunti, include le equazioni non omogenee, sempre partendo dalla relatività
Feynman's different approach to electromagnetism
No full textWe discuss a previously unpublished description of electromagnetism outlined by Richard P. Feynman in the 1960s in five handwritten pages, recently uncovered among his papers, and partly developed in later lectures. Though similar to the existing approaches deriving electromagnetism from special relativity, the present one extends a long way towards the derivation of Maxwell's equations with minimal physical assumptions. {In particular, without postulating Coulomb's law, homogeneous Maxwell's equations are written down} by following a route different from the standard one, i.e. first introducing electromagnetic potentials in order to write down a relativistic invariant action, which is just the inverse approach to the usual one. Also, Feynman's derivation of the Lorentz force exclusively follows from its linearity in the charge velocity and from relativistic invariance. Going further, i.e. adding the inhomogeneous Maxwell's equations, requires some more physical input, and can be done by just following conventional lines, hence this task was not pursued here. Despite its incompleteness, this way of proceeding is of great historical and epistemological significance. We also comment about its possible relevance to didactics, as an interesting supplement to usual treatments
The development of the concept of exchange forces in the 1930s: close encounters between Europe and Japan and the birth of nuclear theory
No full textThe onset and the development of the concept of exchange force in quantum physics are historically reconstructed, starting from Heisenberg’s seminal contributions in 1926 and going through the great developments in nuclear physics, which allowed the emergence of the idea of force mediating virtual quanta. Although most of such work was performed in Europe, the last and decisive effort in this long path was carried out by Japanese scientists in the 1930s. This is the main focus of the present work, which retraces the achievements of Yukawa and Tomonaga, whose results and mutual interactions are carefully analyzed and related to those of European physicists
Measuring a Mass: The Puzzling History of an Elusive Particle
No full textSince Pauli’s hypothesis of their existence in 1930, neutrinos never ceased to bring into play novel ideas and to add new pieces of physics in the whole picture of fundamental interactions. They are only weakly interacting and, at odds with Standard Model’s predictions, have a mass less than one millionth of the electron mass, which makes the investigation of their properties very challenging. The issue of the measurement of neutrino’s rest mass gained a wider and wider consensus since its discovery through neutrino oscillations in 1998. Various neutrino sources are available for experiments, ranging from nuclear collisions of cosmic rays in the Earth atmosphere and supernova explosions to neutrino beams produced by accelerators and power reactors. These suggest different approaches to the experimental detection and measurement of the absolute value of the neutrino mass. In this paper, we retrace the intriguing story of this endeavor, focusing mainly on direct mass determination methods. The puzzling issue of the nature of massive neutrinos is addressed as well with explicit reference to the phenomenon of double beta-decay as a viable experimental tool to discriminate between Dirac’s and Majorana’s nature
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