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Architectural acoustics
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Measurement
(1931)
Der Verfasser untersucht die formalen und materialen Voraussetzungen der Messung in der Physik. Insbesondere sucht er zu zeigen, daß die üblichen Formulierungen, die etwa besagen, daß eine Messung eine Korrelation zwischen Zahlen und nichtnumerischen Gebilden bedeute, oder daß eine Messung im Grunde auf die Feststellung einer raumzeitlichen Koinzidenz hinauslaufe, zum mindesten recht unvollständige Charakterisierungen des physikalischen Verfahrens darstellen; in der Arbeit wird eine genauere Analyse versucht. Diese geht aus von den formalen Eigenschaften der Größenordnung, die jeder Messung zugrunde liegt. Eine geeignete Formulierung dieser Eigenschaften bietet sich dem Verfasser in den zwölf "Axiomen der Quantität" die in der S. 315 angegebenen Gestalt von Hölder aufgestellt worden sind. ...
A new method of measuring compressibility and thermal expansions of liquids has been developed, in which the liquid is enclosed in a sylphon, which is then exposed to external hydrostatic pressure, and the volume change determined from the change of length of the sylphon. This method has been applied to 18 liquids at 0°, 50°, and 95° up to a pressure of 12000 kg, or to the freezing pressure, and the results are collected into extensive tables giving the volume as a function of pressure aand temperature over this range. In the discussion it is shown that small scale differences in the volumes of various isomers persist to high· pressures, and there is no simple connection between the relative densities at atmospheric pressure and at high pressure, The compressibility falls off rapidly with rising pressure, as was found in a preceding investigation. Two liquids are found to have the abnormally low compressibility of water. Thermal expansion also drops off by a large factor with increasing pressure, but not as much as the compressibility, as was also found before. The "pressure coefficient" (δp /δt) , is not a function of volume only, as has often been supposed, and suggestions are made as to the theoretical significance of this.
Energy-budget studies
(1954)
The rotation-vibration model and the hydrodynamic dipole-oscillation model are unified. A coupling between the dipole oscillations and the quadrupole vibrations is introduced in the adiabatic approximation. The dipole oscillations act as a "driving force" for the quadrupole vibrations and stabilize the intrinsic nucleus in a nonaxially symmetric equilibrium shape. The higher dipole resonance splits into two peaks separated by about 1.5-2 MeV. On top of the several giant resonances occur bands due to rotations and vibrations of the intrinsic nucleus. The dipole operator is established in terms of the collective coordinates and the γ-absorption cross section is derived. For the most important 1- levels the relative dipole excitation is estimated. It is found that some of the dipole strength of the higher giant resonance states is shared with those states in which one surface vibration quantum is excited in addition to the giant resonance.
The energies of, and transition probabilities involving, the ground-state rotation bands of Os186, Os188, and Os190 are compared with a diagonalized rotation-vibration theory in which vibrations are considered to three phonon order. Agreement even in the Os transition region is found to be excellent. The theory appears to be particularly successful in predicting two phonon states in Os190.
The unified model and the collective giant-dipole-resonance model are unified. The resulting energy spectrum and the transition probabilities are derived. A new approximate selection rule involving the symmetry of the γ vibrations is established. It is verified that the main observable features in the photon-absorption cross section are not influenced by the odd particle, despite the considerably richer spectrum of states as compared to even-even nuclei.
In heavy nuclei the damping of the giant resonance is due to thermalization of the energy rather than to direct emission of particles; the latter process is strongly inhibited by the angular-momentum barrier. The thermalization proceeds via inelastic collisions leading from the particle-hole state to two-particle-two-hole states. In heavy nuclei, several hundred such states are available at the energy of the giant dipole resonance. The rather large width of the giant resonance arises from the addition of many small partial widths of channels leading to the different two-particle-two-hole states. Both the density of the two-particle-two-hole states and the mean value of the interaction matrix elements between the particle-hole and two-particle-two-hole states are evaluated in a simplified square-well shell model. In a given nucleus the energy dependence of the widths is determined mainly by the density of states; the A dependence is determined mainly by the size of the matrix elements. For A ~ 200, we find 0.5 <= Γ <=2.5 MeV. The uncertainty in this value comes mostly from the uncertainty in the strength of the interaction. Representing the energy dependence of the width by a power law we find for the exponent the value ~ 1.8.
A method is developed for the calculation of resonant nuclear states which preserves as many features of the shell model as possible. It is an extension of the R-matrix theory. The necessary formulas are derived and a detailed description of the computational procedure is given. The method is valid up to the two-particle emission threshold. With the assumption of consecutive decay of the nucleus, the two-particle emission process can also be described. The treatment is antisymmetrized in all particles.