Showing papers by "Technische Universität Darmstadt published in 1980"

Mean-field theory and statistical treatment of residual interactions

Abstract: The time-dependent Hartree-Fock theory is generalized in order to include two-body collisions. Using a method similar to the projection method of quantum statistics an exact and closed equation is derived for the one-particle density matrix which takes into account both the mean field and the two-body residual interactions. In the limit of long mean free path of the particles, the exact equation for the one-particle density matrix is simplified by introducing some general statistical properties of the residual interactions. An equation is obtained for the expectation values of operators which includes both the mean-field contributions and the correlations due to the residual interactions. The effects of the correlations on the fluctuations of collective variables are discussed. It is shown that the statistical approximations introduced do not destroy the energy and the momentum conservations.

A Fast Transaction-Oriented Logging Scheme for Undo Ro overy

Abstract: A special UNDO log algorithm combining the advantages of update in place strategies with the shadow page concept is introduced. It is to support applications demanding high rates of possibly long update transactions as well as fast UNDO recovery. By doubling the disk space for the database, UNDO loggng can be performed with a minimum of additional I/O operations. Thus, we gain a performance comparable to systems without any UNDO loggg. Since in this algorithm one logical slot consists of two physical blocks, the name TWIST (twin slot) algorithm is proposed.

Gamma-spectroscopy within the island of high-spin isomers nearN=82

Abstract: A NaI sum-spectrometer combined with Ge-counters has been used to characterize the members of the island of high spin isomers nearN=82. On the basis of half lives, totalγ-decay energies and discreteγ-lines, assignments of 22 isomers are given or confirmed. The isomers are localized to the region 82≦N≦86 andZ≦68, and the excitation energies vary from 3 MeV to 12.2 MeV. An empirical relation between spin and excitation energy is presented and on this basis isomeric spin values up to (33±2)ħ are deduced. The isomers are thought to be due to strong alignment of 2 to 8 shell-model particles in a spherical or possibly weakly oblate potential.

Fragment spin distribution in 400 MeV40Ar+93Nb collisions investigated by light-particle anisotropies

Abstract: In and out-of-plane angular correlations between light particles and projectile-like fragments from deeply inelastic collisions of 400 MeV40Ar+93Nb were measured. At backward angles, the equilibrium emission of a particles and protons from the target-like fragment was identified. By analysing the out-of-plane angular correlations in the framework of a semi-classical statistical model, an average spin of 30±2ℏ and an average alignment ofP zz =0.80±0.15 for the target-like fragment were deduced.

MO X-ray angular distributions from 1 GeV 208 Pb+ 208 Pb and 209 Bi+ 209 Bi collisions

Abstract: The Doppler shift and the anisotropy of the MO X-rays above the separated-atomK-lines have been measured in208Pb+208Pb and209Bi+209Bi collisions at beam energies between 4.2 and 4.8 MeV/u. The Doppler shift is found to be consistent with a source moving with 90% of the center of mass velocity of the colliding system. One peak is observed in the anisotropy spectrum. This peak might be attributed to transitions from the continuum into the minimum of the 2p 1/2 σ MO or from the 3p 1/2 σ and 2p 3/2 σ MO's into the 2 sσ MO near the united atom limit. Radiative electron capture and secondary electron bremsstrahlung could be excluded as major sources of the observed radiation. Contrary to lighter systems no anisotropy corresponding to transitions into the 1 sσ orbital could be observed.

Atomic collision induced projectile excitation—Its application to identification of heavy ion fusion products

Abstract: Collision induced X-rays are shown to be a useful tool to determine atomic numbers and yields of heavy ion fusion products. In the reaction56Fe(132Xe; xn, yp) the elements Hg, Au, and Pt are produced as primary fusion products. A resolving power Z/ΔZ of 72±7 has been obtained. Improvements and restrictions of the method are discussed.

On the optimality of (z, Z)-order-policies in adaptive inventory control

Abstract: We consider a discrete review single product inventory model in which the distribution of demand is estimated in each period according to the estimate of the last period and the demand observed there. We are interested in the optimality of a (z (t),Z (t))-order-policy behaving as a well-known (s, S)-order-policy from inventory control under risk for fixed estimatet.

Fusion-fission type collisions

Abstract: Three examples of fusion-fission type collisions on medium-.mass nuclei are investigated whether the fragment properties are consistent with fission from equilibrated compound nuclei. Only in a very narrow band of angular momenta the data fulfill the necessary criteria for this process. Continuous evolutions of this mechanism into fusion fission and into a deep-inelastic process and particle emission prior to fusion have been observed. Based on the widths of the fragment-mass distributions of a great variety of data, a further criterion for the compound-nucleus-fission process is tentatively proposed.

Damage to Plain Concrete Under Cyclic Compressive Loading

Abstract: Frequently changing stresses beyond the fatigue limit give rise to material damage. It is assumed that the individual damages of each cycle are accumulated and thus lead to material fatigue. The lifetime of concrete for variable cyclic compressive loadings can be estimated with the help of the linear "cumulative damage hypothesis," if the stress is significantly beyond the assumed fatigue limit. It is not known in which way a stress below the fatigue limit influences the material's lifetime. Furthermore, for concrete up to 10 9 cycles to failure, a significant fatigue limit cannot be established. Due to the required high numbers of cycles a direct clarification by fatigue tests is not possible. Therefore, characteristic values have been determined which describe the development of damage dependent on the degree and frequency of the cyclic compressive load. For this purpose the "acoustic emission analysis" has been applied as well as the direct measured volume alteration method. Thereafter it has been determined if there is a relation between these values and the material lifetime and if statements on the fatigue limit of the concrete can be made.