The European Physical Journal H最新文献

Academician A.?D.?Sakharov’s idea concerning the emission of atomic flux from hot plasma (1951) inspired scientists of A.?F.?Ioffe Physico-Technical Institute to create the first in the world instrument called Neutral Atom Analyzer in 1960 and then in 1961 to use it successfully on the Alpha device (USSR, 1958–1963). Now the analysis of fluxes of fast atoms referred to as Neutral Particle Analysis (NPA) is one of the main diagnostic methods for the ion component of plasma in tokamaks, stellarators, and other devices. NPA provides a unique opportunity for studying the ion distribution functions, ion temperatures and hydrogen isotope ratio in hot plasma. Neutral particle analyzers developed at the Ioffe Institute were widely used in the USSR until the late 1970s, and afterwards began to be employed worldwide. Since then, most of the information on the ion distribution functions and the behavior of fast ions in fusion plasma is obtained from NPA measurements on all leading magnetic confinement fusion systems worldwide. The specialized complex of atom analyzers currently being created at the Ioffe Institute is included in the primary list of ITER diagnostics. The integration of this complex on ITER is expected to begin in 2025.

In this paper, we describe the history of the LHCb experiment over the last three decades, and its remarkable successes and achievements. LHCb was conceived primarily as a ({b} )-physics experiment, dedicated to (CP) violation studies and measurements of very rare ({{b}} ) decays; however, the tremendous potential for ({c} )-physics was also clear. At first data taking, the versatility of the experiment as a general-purpose detector in the forward region also became evident, with measurements achievable such as electroweak physics, jets and new particle searches in open states. These were facilitated by the excellent capability of the detector to identify muons and to reconstruct decay vertices close to the primary ({{p}} {{p}} )?interaction region. By the end of the LHC Run 2 in 2018, before the accelerator paused for its second long shut down, LHCb had measured the CKM quark mixing matrix elements and (CP) violation parameters to world-leading precision in the heavy-quark systems. The experiment had also measured many rare decays of ({b} ) ?and ({c} ) ?quark mesons and baryons to below their Standard Model expectations, some down to branching ratios of order 10(^{-9}). In addition, world knowledge of ({{b}} ) and ({{c}} ) spectroscopy had improved significantly through discoveries of many new resonances already anticipated in the quark model, and also adding new exotic four and five quark states. The paper describes the evolution of the LHCb detector, from conception to its operation at the present time. The authors’ subjective summary of the experiment’s important contributions is then presented, demonstrating the wide domain of successful physics measurements that have been achieved over the years.

We present some historical and philosophical reflections on the paper “On the Relation Between the Expansion and the Mean Density of the Universe”, published by Albert Einstein and Willem de Sitter in 1932. In this famous work, Einstein and de Sitter considered a relativistic model of the expanding universe with both the cosmological constant and the curvature of space set to zero. Although the Einstein-deSitter model went on to serve as a standard model in ‘big bang’ cosmology for many years, we note that the authors do not explicitly consider the evolution of the cosmos in the paper. Indeed, the mathematics of the article are quite puzzling to modern eyes. We consider claims that the paper was neither original nor important; we find that, by providing the first specific analysis of the case of a dynamic cosmology without a cosmological constant or spatial curvature, the authors delivered a unique, simple model with a straightforward relation between cosmic expansion and the mean density of matter that set an important benchmark for both theorists and observers. We consider some philosophical aspects of the model and provide a brief review of its use as a standard ‘big bang’ model over much of the (20{mathrm {th}}) century.

In this admittedly personal account of the history of atomistic simulations of fluids (at the atomic or molecular level), I will focus on the competing efforts to reach the boundary between atoms and the continuum. The prevailing wisdom was that thermal fluctuations at the atomistic scale—both time (a few mean collision times) and space (a few atomic spacings)—would make the connection virtually impossible. This is just a part of the story about how molecular dynamics was able to connect to Navier–Stokes–Fourier hydrodynamics. Resistance in the theoretical physics community to computer simulations of equilibrium fluids at the atomistic scale was only exceeded by the even stiffer objections to non-equilibrium molecular-dynamics simulations: after the fifty years from Boltzmann to molecular dynamics, it took another quarter century to overcome the doubts.

Nikhilranjan Sen (1894–1963), popularly known as N.R. Sen, is known as the Father of Applied Mathematics and founder of the Calcutta School of Relativity Theory. He did Ph.D. in Berlin under the Nobel Laureate Max von Laue. In Berlin he came in contact with renowned physicists like Max Planck, Albert Einstein and their contemporaries. The present article, which is based on the primary sources, discusses the lesser known facts of his life, like the beginning of scientific career, background of his D.Sc. as well as Ph.D. theses, and detailed summary of his scientific works.

Editor’s note: One of the most important developments in theoretical particle physics at the end of the 20th century and beginning of the twenty-first century has been the development of effective field theories (EFTs). Pursuing an effective field theory approach is a methodology for constructing theories, where a set of core principles is agreed upon, such as Lorentz symmetry and unitarity, and all possible interactions consistent with them are then compulsory in the theory. The utility of this approach to particle physics (and beyond) is wide ranging and undisputed, as evidenced by the recent formation of the international seminar series All Things EFT (Talks in the series can be viewed at https://www.youtube.com/channel/UC1_KF6kdJFoDEcLgpcegwCQ (accessed 21 December 2020).) which brings together each week the worldwide community of EFT practitioners. The text below is a lightly edited version of the talk given by Prof. Weinberg on September 30, 2020, which inaugurated the series. The talk reviews some of the early history of EFTs from the perspective of its pioneer and concludes with a discussion of EFT implications for future discovery.

This is a tutorial for the many-worlds theory by Everett, which includes some of my personal views. It has two main parts. The first main part shows the emergence of many worlds in a universe consisting of only a Mach–Zehnder interferometer. The second main part is an abridgment of Everett’s long thesis, where his theory was originally elaborated in detail with clarity and rigor. Some minor comments are added in the abridgment in light of recent developments. Even if you do not agree to Everett’s view, you will still learn a great deal from his generalization of the uncertainty relation, his unique way of defining entanglement (or canonical correlation), his formulation of quantum measurement using Hamiltonian, and his relative state.

In the late 1970s, the embryonic UK research community in molecular simulation – physicists and physical chemists – organised itself around CCP5, one of a set of Collaborative Computational Projects in different fields. CCP5 acted to develop and use the software required by an evolving and expanding scientific agenda, to exploit quickly and efficiently the revolution in computing hardware and to educate and nurture the careers of future generations of researchers in the field. This collaboration formally began in 1980, and is still fully active now, 40 years later. Today, molecular simulation techniques, many of them pioneered by CCP5, are now used very widely, including in several other CCPs in the UK’s current family of Collaborative Computational Projects. This article tells the story of molecular simulation in the UK, with CCP5 itself at centre stage, using the written records in the CCP archives. The authors were, or are, all personally involved in this story.

The widespread positivist approach of physics research in Italy at the turn of the XIX and XX centuries did not provide a fertile ground for the scientific debate on the atomic structure of matter, which instead raged beyond the Alps in those same years and which gave birth, during the 1920s, to the quantum revolution. Experimental investigations in spectroscopy and radioactivity were carried out with discrete success in the 1910s and early 1920s by Italian physicists such as Antonino Lo Surdo and Rita Brunetti in Florence, stimulating an empirical knowledge of early quantum theory and the acquisition of the related laboratory skills. However, the theoretical framework necessary for the reception and development of the postulates and formalisms of quantum mechanics started to be cultivated in Italy with a delay of a few decades compared to Central European countries. The diffusion of quantum studies – with their unprecedented drive toward an integration of experiment and theory – took hold in Italy beginning from the establishment of the first theoretical physics chairs (1926) at the Universities of Rome, Florence and Milan, whose origins are here described in detail. Furthermore, the present paper presents a systematic analysis of the appearance of the quantum mechanical concepts in Italian university courses between 1927 and 1947.

In 1921, the experimental physicist Rudolf Ladenburg put forward the first quantum interpretation of optical dispersion. Theoretical physicists had tried to explain dispersion from the point of view of quantum theory ever since 1913, when Niels Bohr proposed his quantum model of atom. Yet, their theories proved unsuccessful. It was Ladenburg who gave a breakthrough step toward our quantum understanding of dispersion. In order to understand Ladenburg’s step, I analyze Ladenburg’s experimental work on dispersion prior to 1913, the reasons why the first theories of dispersion after 1913 were not satisfactory, and Ladenburg’s 1921 proposal. I argue that Ladenburg’s early experimental work on dispersion is indispensable to understand his 1921 paper. The specific kind of experiments he performed before 1913, the related interpretative problems, and the way he tried to solve them, led him reapproach the dispersion problem in 1921 in a way that was completely different from the way theoretical physicists had done it before.