1,723,055 research outputs found
Covariant Majorana Formulation of Electrodynamics
Full text linkWe construct an explicit covariant Majorana formulation of Maxwell
electromagnetism which does not make use of vector 4-potential. This allows to
write a ``Dirac'' equation for the photon containing all the known properties
of it. In particular, the spin and (intrinsic) boost matrices are derived and
the helicity properties of the photon are studied.Comment: 12 pages, Latex2
History teaches: Some educational projects based on the history of physics
Full text linkWe present some projects carried out in recent years and aimed at students of different levels (from high school to university), where we have adopted well-defined historical paths. The basic aim is to allow the students involved to
develop appropriate physical reasoning skills, without the preventive request of a good standard preparation of the topics covered. The lines of action which were common to the various projects were intended to encourage the students to: 1) think like the given scientist of the past who is the object of the project, building step by step proper knowledge and reasoning; 2) work like that scientist, performing the original experiments; 3) deduce just as that scientist did concerning the subject matter; 4) present the results of their activity (including Physics demonstrations)
to other students and, in general, to the general public, in order to test their ability to communicate what they have learned and discovered. These educational goals have always been accompanied by the desire to carry out historically consistent activities, based on the awareness of the key role that the history of physics can play in promoting scientific understanding at a deep level, even without requiring particular mathematical knowledge or advanced preparation. The enthusiasm of the students involved in the various projects, especially in demonstrating the result of
their work to other students or in public events, as well as the prompt involvement of the aforementioned public (lacking adequate preparation or specific knowledge in the proposed activity), undoubtedly testify in favor of the success of the work presented here
Ettore Majorana: unveiled genius and endless mysteries
No full textThis biography sheds new light on the life and work of physicist Ettore Majorana (including unpublished contributions), as well as on his mysterious disappearance in March 1938. Majorana is held by many, including Nobel Laureate, Enrico Fermi, to have been a genius of the rank of Galilei and Newton. In this intriguing story, the author, himself a leading expert on the work of Majorana, supplements the existing literature with new insights, anecdotes and personal accounts of contemporaries of Majorana
A theory of ferromagnetism by Ettore Majorana
No full textWe present and analyze in detail an unknown theory of ferromagnetism developed by Ettore Majorana as early as the beginnings of 1930s, substantially different in the methods employed from the well-known Heisenberg theory of 1928 (and from later formulations by Bloch and others). Similarly to this, however, it describes Successfully the main features of ferromagnetism, although the key equation for the spontaneous mean magnetization and the expression for the Curie temperature are different from those deduced in the Heisenberg theory (and in the original phenomenological Weiss theory). The theory presented here contains also a Peculiar prediction for the number of nearest neighbors required to realize ferromagnetism, which avoids the corresponding arbitrary assumption made by Heisenberg on the basis of known (at that time) experimental observations. Some applications of the theory (linear chain, triangular chain, etc.) are, as well, considered. (C) 2008 Elsevier Inc. All rights reserved
Fleeting genius
No full textEttore Majorana is considered as a genius who made contributions to neutrino physics. He was born on 5th August, 1906 in Catania, Sicily with a rich scientific and technical background. He, along with Enrico Fermi developed statistical model of atoms that came to be known as Thomas-Fermi model, which describes the energy of an atom in terms of the density of its surrounding electrons by way of a complicated nonlinear differential equation. He made substantial theoretical contributions to researches and published his first paper, in which he calculated the splitting of certain spectroscopic properties of gadolinium, uranium, and cesium due to the spin of electrons. He also published an article entitled Relativistic theory of particles with arbitrary intrinsic momentum, which became a major contribution to group theory. His research activity focused on field theory and quantum electrodynamics
Numerical prediction of plasma formation on a sphere in hypersonic sub-orbital flight regime
Full text linkHypersonic flight is challenging for vehicle design and operation due to the intense heating generated by kinetic energy transfer from the vehicle to the gas surrounding it. As a result, plasma is produced, which can interfere with radar tracking and communication, particularly upon re-entry into the Earth’s atmosphere. Plasma affects wave propagation, and if the electron density is high enough, waves may lose intensity as they propagate, distorting radar traces. The objective of this research is to predict plasma formation during suborbital hypersonic flight, with a specific focus on determining the Mach number and altitude conditions that generate critical levels of plasma density. To achieve this, Computational Fluid Dynamics is employed to solve the Navier-Stokes equations, and a multi-temperature thermochemical model is adopted to accurately predict plasma behavior. The model is applied in a simplified scenario involving a sphere exposed to hypersonic flow
On the role of spin in quantum mechanics
No full textFrom the invariance properties of the Schrodinger equation and the isotropy of space we show that a generic (non-relativistic) quantum system is endowed with an "external" motion, which can be interpreted as the motion of the centre of mass, and an "internal" one, whose presence disappears in the classical limit. The latter is caused by the spin of the particle, whatever is its actual value (different from zero). The quantum potential in the Schrodinger equation, which is responsible of the quantum effects of the system, is then completely determined from the properties of the internal motion and its "unusual" properties have a simple and physical explanation in the present context. From the impossibility to fix the initial conditions relevant for the internal motion follows, finally, the need of a probabilistic interpretation of quantum mechanics
Searching for an equation: Dirac, Majorana and the others
No full textWe review the non-trivial issue of the relativistic description of a quantum mechanical system that, contrary to a common belief, kept theoreticians busy from the end of 1920s to (at least) mid 1940s. Starting by the well-known works by Klein-Gordon and Dirac, we then give an account of the main results achieved by a variety of different authors, ranging from de Broglie to Proca, Majorana, Fierz-Pauli, Kemmer, Rarita-Schwinger and many others. A particular interest comes out for the general problem of the description of particles with arbitrary spin, introduced (and solved) by Majorana as early as 1932, and later reconsidered, within a different approach, by Dirac in 1936 and by Fierz-Pauli in 1939. The final settlement of the problem in 1945 by Bhabha, who came back to the general ideas introduced by Majorana in 1932, is discussed as well, and, by making recourse also to unpublished documents by Majorana, we are able to reconstruct the line of reasoning behind the Majorana and the Bhabha equations, as well as its evolution. Intriguingly enough, such an evolution was identical in the two authors, the difference being just the period of time required for that: probably few weeks in one case (Majorana), while more than ten years in the other one (Bhabha), with the contribution of several intermediate authors. The important unpublished contributions by Majorana anticipated later results obtained, in a more involved way, by de Broglie (1934) and by Duffin and Kemmer (1938-9), and testify the intermediate steps in the line of reasoning that led to the paper published in 1932 by Majorana, while Bhabha took benefit of the corresponding (later) published literature. Majorana's paper of 1932, in fact, contrary to the more complicated Dirac-Fierz-Pauli formalism, resulted to be very difficult to fully understand (probably for its pregnant meaning and latent physical and mathematical content): as is clear from his letters, even Pauli (who suggested its reading to Bhabha) took about one year in 1940-1 to understand it. This just testifies for the difficulty of the problem, and for the depth of Majorana's reasoning and results. The relevance for present day research of the issue here reviewed is outlined as well. (C) 2012 Elsevier Inc. All rights reserved
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