The European Physical Journal H最新文献

A view on the physical meaning of the so called ergodic hypothesis: its role on thefoundations of equilibrium statistical mechanics in mid ’1800, its interpretations andhints at its relevance for modern nonequilibrium statistical mechanics. Followed byappendices with detailed comments on the original papers.

Results from neutrino experiments at CERN in the1970’s, using bubble chamber detectors filled with heavy liquids, gave early evidence for the existence of quarks and gluons as real dynamical objects. In detail, the measured moments of the non-singlet structure functions provided crucial support for the validity of the present theory of the strong inter-quark interactions, quantum chromodynamics.

This article offers a review of the history of radar research and its application in the20th century. After describing the wartime work of Sin-Itiro Tomonaga and his theory ofthe cavity magnetron, we formulate the equations of motion of an electron in a cavitymagnetron using action-angle variables. This means following the electron’s path on itsway from a cylindrical cathode moving toward a co-axial cylindrical anode in presence of auniform magnetic field parallel to the common axis. After analyzing the situation withoutcoupling to an external oscillatory electric field, we employ methods of canonicalperturbation theory to find the resonance condition between the frequencies of the freetheory ω _r , ω _? and the applied perturbing oscillatory frequency ω. A long-time averagingprocess will then eliminate the periodic terms in the equation for the now time-dependentaction-angle variables. The terms that are no longer periodic will cause secular changesso that the canonical action-angle variables (J, δ) change in a way that the path of the electronwill deform gradually so that it can reach the anode. How the ensemble of the initiallyrandomly distributed electrons forms spokes and how their energy is conveyed to thecavity-field oscillation is the main focus of this article. Some remarks concerning theimportance of results in QED and the invention of radar theory and application concludethe article.

Neutrino physics with high energy neutrino beams has played a crucial role inestablishing the Standard Model of the electroweak interaction, in particular withrepeated measurements of increasing precision of the fundamental parameter sin² θ _W which defines theelectroweak mixing. This paper relates the history of these measurements, from thediscovery of the neutral current interaction in 1973 until the latest high precisionmeasurements in the years 2000. The review discusses in chronological order the importantexperiments performed at CERN, Fermilab and Brookhaven during the last thirty years of the20th century.

We analyze the collaboration between Bohr and Ehrenfest on the quantum theory in theearly 1920s (1920–1923). We focus on their reflections and developments around theadiabatic principle and the correspondence principle, the two pillars of Bohr’s quantumtheory of 1922–23. We argue that the evolution of Bohr’s ideas after 1918 brought the twoprinciples closer, subordinating the former to the latter. The examination of the weightBohr attributed to each principle along the years illustrates very clearly thevicissitudes of Bohr’s theory before the emergence of quantum mechanics, especially withregards to its rejection/inclusion of mechanics.

I will discuss the evolution of the definitions of time, time interval, and frequency from antiquity to the present day. The earliest definitions of these parameters were based on a time interval defined by widely observed apparent astronomical phenomena, so that techniques of time distribution were not necessary. With this definition, both time, as measured by clocks, and frequency, as realized by some device, were derived quantities. On the other hand, the fundamental parameter today is a frequency based on the properties of atoms, so that the situation is reversed and time and time interval are now derived quantities. I will discuss the evolution of this transition and its consequences. In addition, the international standards of both time and frequency are currently realized by combining the data from a large number of devices located at many different laboratories, and this combination depends on (and is often limited by) measurements of the times of clocks located at widely-separated laboratories. I will discuss how these measurements are performed and how the techniques have evolved over time.

The Korcak-law – first presented in an empirical form in 1938 to describe the size-distribution of various geographical objects, including lakes and islands by Jaromír Kor?ák – was one of the examples used by Benoit Mandelbrot to show that fractals are not only mathematical monsters, but that they are applicable to describe many natural objects and phenomena too. In this paper, we would like to give a brief overview about the history of the Korcak-law and its connection to other similar rules. Moreover, we would like to show, that although there are similarities between fractal-related laws and the Korcak-law, the Korcak-exponent is not directly related to fractal dimension. In this sense, the measure introduced by Benoit Mandelbrot based on Kor?ák’s empirical findings is not a fractal measure.

In 1995, Michel Mayor and Didier Queloz announced they discovered 51 Pegasi b, the first planet ever found around a star other than the Sun. This discovery turned out to be a milestone of recent astronomy, as it opened up a new field of research that is growing impressively these days. However, 51 Pegasi b has surprising properties as compared to the planets of the Solar System, as it is a giant planet on a very close-in orbit around its parent star. Hence, its discovery was unexpected and its actual existence did not go unchallenged. In the following years, a passionate debate sprang up, and finally astronomers accepted it, but at the price of a deep revision of our understanding of how planetary systems are formed and evolve. In the present paper, we reconstruct the dynamics of the discovery of 51 Pegasi b and the first exoplanets, the quarrel that arose among astronomers and the final acceptance of the existence of planets with unexpected characteristics. This remarkable story is recounted by means of published literature as well as interviews with several of its main protagonists.