G eant 4 is a toolkit for simulating the passage of particles through matter. It includes a complete range of functionality including tracking, geometry, physics models and hits. The physics processes offered cover a comprehensive range, including electromagnetic, hadronic and optical processes, a large set of long-lived particles, materials and elements, over a wide energy range starting, in some cases, from 250 eV and extending in others to the TeV energy range. It has been designed and constructed to expose the physics models utilised, to handle complex geometries, and to enable its easy adaptation for optimal use in different sets of applications. The toolkit is the result of a worldwide collaboration of physicists and software engineers. It has been created exploiting software engineering and object-oriented technology and implemented in the C++ programming language. It has been used in applications in particle physics, nuclear physics, accelerator design, space engineering and medical physics.

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Geant4—a simulation toolkit

Geant4 - A Simulation Toolkit

* Caring for children * The origins of attachment theory * Psychoanalysis as art and science * Psychoanalysis as a natural science * Violence in the family * On knowing what you are not supposed to know and feeling what you are not supposed to feel * The role of attachment in personality development * Attachment, communication, and the therapeutic process * Developmental psychiatry comes of age

A Secure Base. Parent-Child Attachment and Healthy Human Development. New York (Basic Books) 1988.

More is different.

Feshbach resonances are the essential tool to control the interaction between atoms in ultracold quantum gases. They have found numerous experimental applications, opening up the way to important breakthroughs. This review broadly covers the phenomenon of Feshbach resonances in ultracold gases and their main applications. This includes the theoretical background and models for the description of Feshbach resonances, the experimental methods to find and characterize the resonances, a discussion of the main properties of resonances in various atomic species and mixed atomic species systems, and an overview of key experiments with atomic Bose-Einstein condensates, degenerate Fermi gases, and ultracold molecules.

Feshbach resonances in ultracold gases

The influence on the h.f.s. of the finite size of the nucleus is considered and the effect is calculated for simple models of the nuclear magnetism. It is pointed out that the distribution of magnetic dipole density over the nuclear volume may vary greatly from nucleus to nucleus depending on the relative contributions of spin and orbital magnetic moments to the total nuclear moment. On this basis an attempt is made to interpret the observed discrepancy between the h.f.s. ratio of the Rb isotopes and the ratio of the magnetic moments as determined by the magnetic resonance method. A study of such anomalies may give some information regarding the structure of nuclear moments, in particular, regarding the nuclear ${g}_{L}$-factor.

The Influence of Nuclear Structure on the Hyperfine Structure of Heavy Elements

Die in einer vorangehenden Arbeit* durchgefuhrte Berechnung der naturlichen Linienbreite auf Grund der Diracschen Lichttheorie wird auf zwei Spezialfalle erweitert, die in 1. c. nicht behandelt werden konnten. Dabei ergab sich, das die Breite der Linie eines harmonischen Oszillators mit der nach der klassischen Theorie berechneten vollkommen ubereinstimmt.

Über die natürliche Linienbreite in der Strahlung des harmonischen Oszillators

Reactor safety study

The charge distribution, the electromagnetic field and the self-energy of an electron are investigated. It is found that, as a result of Dirac's positron theory, the charge and the magnetic dipole of the electron are extended over a finite region; the contributions of the spin and of the fluctuations of the radiation field to the self-energy are analyzed, and the reasons that the self-energy is only logarithmically infinite in positron theory are given. It is proved that the latter result holds to every approximation in an expansion of the self-energy in powers of $\frac{{e}^{2}}{\mathrm{hc}}$. The self-energy of charged particles obeying Bose statistics is found to be quadratically divergent. Some evidence is given that the "critical length" of positron theory is as small as $\frac{h}{(\mathrm{mc})}\ifmmode\cdot\else\textperiodcentered\fi{}\mathrm{exp}(\frac{\ensuremath{-}hc}{{e}^{2}})$.

On the Self-Energy and the Electromagnetic Field of the Electron

We discuss the interaction of hadrons with leptons in the limit of large momentum transfer. A special parton model will be used for the hadrons in which the partons are identified with quarks. The relativistic quark model with which we interpret recent observations is formulated as follows: (1) The baryons are composed of three valence quarks and a core of an indefinite number of quark-antiquark pairs. (2) The lepton "sees" the nucleon in the limit of large momenta in the c.m. frame as an assembly of freely moving constitutents with point charges. (3) The scattering of the valence quarks is interpreted as the nondiffractive component, the scattering of the core is interpreted as the diffractive component of the cross section. (4) The nondiffractive scattering is assumed to be mediated by suitable meson exchanges, and this assumption determines the momentum distribution of the valence quarks. The ($q\overline{q}$) pairs in the core are assumed to be distributed statistically in the available phase space. (5) It will be necessary to include "gluons" among the constituents of the nucleon. They are supposed to be the uncharged quanta of the force field between quarks and are assumed to be distributed statistically over the momentum space. There is only one constant adjustable in this model, which is the ratio of gluons to core pairs. All other constants are fixed by simple considerations. This model is used to calculate the deep-inelastic scattering of electrons by protons and neutrons and its dependence on the relative spin orientations, the inelastic scattering of neutrinos by nucleons, and the creation of massive muon pairs by proton-proton collisions. After adjusting the open constant to the data of electron-proton scattering, the theory predicts unambiguously the other results. They are in reasonably good agreement with the observations as far as they are known.

Victor F. Weisskopf

Papers

The Influence of Nuclear Structure on the Hyperfine Structure of Heavy Elements

Über die natürliche Linienbreite in der Strahlung des harmonischen Oszillators

Reactor safety study

On the Self-Energy and the Electromagnetic Field of the Electron

Inelastic lepton--nucleon scattering and lepton pair production in the relativistic quark--parton model.