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

A semi-empirical basis is used to describe and correlate the known nuclear properties including the theoretical concepts, methods, and considerations which have been devised in order to interpret the experimentsl material and to advance the ability to predict and control nuclear phenomena. General properties, two-body problems at low energies, nuclear forces, two-body problems at high energies, three- and four-body problems, nuclear spectroscopy, nuclear reactions, spontaneous decay of nuclei, interaction of nuclei with electromagnetic radiation, and beta decay are treated. 1200 references. (JFP)

Theoretical Nuclear Physics

We propose that a strongly interacting particle is a finite region of space to which fields are confined. The confinement is accomplished in a Lorentz-invariant way by endowing the finite region with a constant energy per unit volume, $B$. We call this finite region a "bag." The contained fields may be either fermions or bosons and may have any spin; they may or may not be coupled to one another. Equations of motion and boundary conditions are obtained from a variational principle. The confining region has no dynamical freedom but constrains the fields inside: There are no excitations of the coordinates determining the confining region. The model possesses many desirable features of hadron dynamics: (i) a parton interpretation and presumably Bjorken scaling; the confined fields are free or weakly interacting except close to the boundary; (ii) infinitely rising Regge trajectories as a consequence of the bag's finite extent; (iii) the Hagedorn degeneracy or limiting temperature; (iv) all physical hadrons are singlets under hadronic gauge symmetries. For example, in a theory of fractionally charged, "colored" quarks interacting with colored, massless gauge vector gluons, if both quark and gluon fields are confined to the bag, only color-singlet solutions exist. In addition to establishing these general properties, we present complete classical and quantum solutions for free scalars and also for free fermions inside a bag of one space and one time dimension. Both systems have linear mass-squared spectra. We demonstrate Poincar\'e invariance at the classical level in any dimension and at the quantum level for the above-mentioned explicit solutions in two dimensions. We discuss the behavior of specific solutions in one and three space dimensions. We also discuss in detail the problem of fermion boundary conditions, which follow only indirectly from the variational principle.

New extended model of hadrons

Es werden die Diracschen Gleichungen der Wechselwirkung zwischen Atom und Strahlung in einer von der ublichen verschiedenen Art naherungsweise gelost. Die Losungen gelten wahrend der ganzen Zeit, die fur die Emission praktisch in Betracht kommt, mit der gleichen Naherung und liefern den Intensitatsverlauf in den Emissionslinien des Atoms.

Calculation of the natural brightness of spectral lines on the basis of Dirac's theory

Experiments by Lark-Horovitz and collaborators on the Hall effect and resistivity of germanium semiconductors have shown that the simple theory of lattice scattering alone cannot explain the temperature dependence of the resistivity. Another probable source of resistance is scattering by ionized impurity centers. This resistance can be calculated by using the Rutherford scattering formula. Evaluation of the collision terms in the Lorentz-Boltzmann equation of state is made by assuming that scattering of an electron by one ion is approximately independent of all other ions. This results in a resistivity given by (in ohm cm): $\ensuremath{\rho}=2.11\ifmmode\times\else\texttimes\fi{}{10}^{2}{\ensuremath{\kappa}}^{\ensuremath{-}2}{T}^{\ensuremath{-}\frac{3}{2}}\mathrm{ln}{1+36{\ensuremath{\kappa}}^{2}{d}^{2}{(\mathrm{kT})}^{2}{e}^{\ensuremath{-}4}}$ where $d$ is half the average distance between impurity ions and $\ensuremath{\kappa}$ the dielectric constant of the semiconductor.

Theory of Impurity Scattering in Semiconductors

It is possible to apply statistical methods to the calculation of nuclear processes provided that the energies involved are large in comparison with the lowest excitation energies of nuclei Expressions are obtained for the emission probability of neutrons or charged particles by highly excited heavy nuclei These expressions are built up in a similar way to the formula for the probability of evaporation of a particle from a body at low temperatures In applying it to the impact of high energy neutrons on heavy nuclei, the mean energy loss per impact turns out to be $E[1\ensuremath{-}2{(\frac{a}{E})}^{\frac{1}{2}}]$ where $E$ is the energy of the incident neutrons and $a$ is dependent on the nuclear structure; we can put approximately $a\ensuremath{\sim}005\ensuremath{-}02$ MV The energy distribution of the scattered neutrons is approximately a Maxwellian one with a mean energy of $2{(\mathrm{aE})}^{\frac{1}{2}}$

Victor F. Weisskopf

Papers

Theoretical Nuclear Physics

New extended model of hadrons

Calculation of the natural brightness of spectral lines on the basis of Dirac's theory

Theory of Impurity Scattering in Semiconductors

Statistics and Nuclear Reactions