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Featured researches published by Enrico Fermi.


The Astrophysical Journal | 1953

Problems of Gravitational Stability in the Presence of a Magnetic Field

S. Chandrasekhar; Enrico Fermi

In this paper a number of problems are considered which are related to the gravitational stability of cosmical masses of infinite electrical conductivity in which there is a prevalent magnetic field. In Section I the virial theorem is extended to include the magnetic terms in the equations of motion, and it is shown that when the magnetic energy exceeds the numerical value of the gravitational potential energy, the configuration becomes dynamically unstable. It is suggested that the relatively long periods of the magnetic variables may be due to the magnetic energy of these stars approaching the limit set by the virial theorem. In Section II the adiabatic radial pulsations of an infinite cylinder along the axis of which a magnetic field is acting is considered. An explicit expression for the period is obtained. Section III is devoted to an investigation of the stability for transverse oscillations of an infinite cylinder of incompressible fluid when there is a uniform magnetic field acting in the direction of the axis. It is shown that the cylinder is unstable for all periodic deformations of the boundary with wave lengths exceeding a certain critical value, depending on the strength of the field. The wave length of maximum instability is also determined. It is found that the magnetic field has a stabilizing effect both in increasing the wave length of maximum instability and in prolonging the time needed for the instability to manifest itself. For a cylinder of radius R = 250 parsecs and p = 2 × 10-24 gm/cm3 a magnetic field in excess of 7 × l0-6 gauss effectively removes the instability. In Section IV it is shown that a fluid sphere with a uniform magnetic field inside and a dipole field outside is not a configuration of equilibrium and that it will tend to become oblate by contracting in the direction of the field. Finally, in Section V the gravitational instability of an infinite homogeneous medium in the presence of a magnetic field is considered, and it is shown that jeanss condition is unaffected by the presence of the field.


The Astrophysical Journal | 1953

Magnetic fields in spiral arms

S. Chandrasekhar; Enrico Fermi

In this paper two independent methods are described for estimating the magnetic field in the spiral arm in which we are located. The first method is based on an interpretation of the dispersion (of the order of 10° ) in the observed planes of polarization of the light of the distant stars; it leads to an estimate of H = 7.2 X 10 -6 gauss. The second method is based on the requirement of equilibrium of the spiral arm with respect to lateral expansion and contraction: it leads to an estimate of H = 6 X 10 -6 gauss.


Il Nuovo Cimento | 1934

Sopra lo Spostamento per Pressione delle Righe Elevate delle Serie Spettrali

Enrico Fermi

SantoLo spostamento dei termini elevati delle serie di assorbimento dei vapori alcalini, osservato daAmaldieSegrèquando il vapore si trova in una atmosfera di gas estraneo, viene studiato teoricamente. Si stabilisce una relazione tra lo spostamento delle righe e la sezione d’urto limite per elettroni di velocità piccolissima contro le molecole del gas perturbatore.


Il Nuovo Cimento | 1934

Tentativo di una Teoria Dei Raggi β

Enrico Fermi

SuntoSi propone una teoria quantitativa dell’emissione dei raggi \ in cui si ammette l’esistenza del « neutrino » e si tratta l’emissione degli elettroni e dei neutrini da un nucleo all’alto della disintegrazione β con un procedimento simile a quello seguito nella teoria dell’ irradiazione per descrivere l’emissione di un quanto di luce da un atomo eccitato. Vengono dedotte delle formule per la vita media e per la forma dello spettro continuo dei raggi β, e le si confrontano coi dati sperimentali.


Archive | 1934

Versuch einer Theorie der β-Strahlen. I

Enrico Fermi

Eine quantitative Theorie des β-Zerfalls wird vorgeschlagen, in welcher man die Existenz des Neutrinos annimmt, und die Emission der Elektronen und Neutrinos aus einem Kern beim β-Zerfall mit einer ah


European Physical Journal | 1926

Zur Quantelung des idealen einatomigen Gases

Enrico Fermi

ZusammenfassungWenn der Nernstsche Wärmesatz auch, für das ideale Gas seine Gültigkeit behalten soll, muß man annehmen, daß die Gesetze idealer Gase bei niedrigen Temperaturen von den klassischen abweichen. Die Ursache dieser Entartung ist in einer Quantelung der Molekularbewegungen zu suchen. Bei allen Theorien der Entartung werden immer mehr oder weniger willkürliche Annahmen über das statistische Verhalten der Moleküle, oder über ihre Quantelung gemacht. In der vorliegenden Arbeit wird nur die von Pauli zuerst ausgesprochene und auf zahlreiche spektroskopische Tatsachen begründete Annahme benutzt, daß in einem System nie zwei gleichwertige Elemente vorkommen können, deren Quantenzahlen vollständig übereinstimmen. Mit dieser Hypothese werden die Zustandsgieichung und die innere Energie des idealen Gases abgeleitet; der Entropiewert für große Temperaturen stimmt mit dem Stern-Tetrodeschen überein.


European Physical Journal | 1933

Zur Theorie der Hyperfeinstruktur

Enrico Fermi; Emilio Segrè

ZusammenfassungDie Hyperfeinstrukturen der Elemente: Li, Na, Cu, Ga, Rb, Cd, In, Cs, Ba, Au, Hg, Tl, Pb, Bi, die experimentell gut bekannt und für die Theorie relativ leicht zugänglich sind, werden untersucht. Insbesondere wird diskutiert, wie weit die beobachteten Hyperfeinstrukturen bereits mit der Hypothese eines magnetischen Kernmoments gedeutet werden können. Es ergibt sich, daß die Hypothese einer magnetischen Kopplung in keinem Falle mit den experimentellen Resultaten in Widerspruch ist, wenn man den zahlreichen Störungen, auch zwischen verschiedenen Elektronenkonfigurationen, Rechnung trägt; sie reicht aus, um die allgemeinen Züge des gesamten Beobachtungsmaterials wiederzugeben, doch kann man die Möglichkeit nicht ausschließen, daß andere Umstände noch kleine Störungen bedingen. Schließlich wird betrachtet, welche Schlüsse man aus den Experimenten auf die magnetischen Momente der Kerne ziehen kann.


European Physical Journal | 1932

Über die Wechselwirkung von zwei Elektronen

H. Bethe; Enrico Fermi

ZusammenfassungDie Zusammenhänge zwischen den Wechselwirkungsformeln von Breit und Møller und der Quantenelektrodynamik werden diskutiert. Es wird gezeigt, daß die Breitsche Formel sich aus der Møllerschen (§ 1) und aus der Quantenelektrodynamik (§ 2) ableiten läßt, und daß aus der letzteren auch die Møllersche Formel folgt (§ 3).


European Physical Journal | 1930

Über das Intensitätsverhältnis der Dublettkomponenten der Alkalien

Enrico Fermi

ZusammenfassungNach den bekannten Intensitätsregeln sollte das Intensitätsverhältnis der Komponenten für alle Dublette der Hauptserie der Alkalien 2∶1 sein. Die experimentell gefundenen Verhältnisse weichen, hauptsächlich bei Cäsium, sehr weit von dem theoretischen Werte ab. In vorliegender Arbeit wird diese Unstimmigkeit zwischen Theorie und Experiment erklärt.


American Journal of Physics | 1952

Experimental Production of a Divergent Chain Reaction

Enrico Fermi

Except for minor editorial revisions this paper is the reproduction of a report written for the Metallurgical Laboratory of the University of Chicago almost ten years ago, after the experimental production of a divergent chain reaction. This report has now been declassified and can be published. The present first part of the report contains a general description of the first pile and of its operation. The details of the construction, preparation, and testing of the materials and of the instrumentation are given by the members of the groups responsible for the work in Appendices I and II. The pile had approximately the shape of a flattened ellipsoid of graphite having 388-cm equatorial radius and 309-cm polar radius. The uranium was distributed through the graphite mass in lumps partly of metal and partly of oxide arranged in a cubic lattice array with about 21-cm cell side. The experimental procedure followed in approaching the critical dimensions and in the actual operation of the pile is described. The observed critical dimensions are compared with the expectation from the tests on the various components of the structure.

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Edward Teller

Lawrence Livermore National Laboratory

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Emilio Segrè

University of California

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G.B. Yodh

University of Chicago

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A. Lundby

University of Chicago

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