Untersuchung der Reaktionen32S(n, αo)29Si und40Ca(n, αo)37Ar beiE n=13,9 MeV mit einem Plattenzählerteleskop

The reactions³²S(n, α)²⁹Si and⁴⁰Ca(n, α)³⁷Ar were studied with 13.9 MeV neutrons using two different counter telescopes. Absolute differential cross sections were measured for the transitions to the ground states of²⁹Si and³⁷Ar and to the 1.27+2.03+2.42 MeV levels of²⁹Si. The angular distribution of the ground states interpreted in terms of a simple pick-up-reaction-model were compared with a DWBA-calculation using the code DWUCK.     

Influence of excitation wavelength on the reflectivity of photogenerated plasmas in germanium

High-density carriers were produced in germanium using the fundamental (1.06 μm) and second harmonic (0.53 μm) output of a Q-switched glass:Nd³⁺ laser. Differences in the plasma reflectivity at 10.6 μm are attributed to different amounts of lattice heating. In particular, the more substantial damping of the plasma resonance associated with the 0.53 μm excitation is attributed to a higher electron-phonon collision frequency. The results are discussed with respect to diagnostics of photogenerated semiconductor plasmas and the effeciency of semiconductor switches.     

Der Wärmeübergang im Post-Dryout-Gebiet während transienter Vorgänge

Zusammenfassung Werden in einem beheizten Verdampferrohr die Randbedingungen so geändert, daß sich der Ort der Siedekrise in Strömungsrichtung verschiebt, so kann dies vorübergehend zu einer starken Reduktion des Wärmeübergangskoeffizienten im Post-Dryout-Gebiet führen. Es werden die an einem Hochdruckkreislauf gewonnenen zeitlichen Verläufe der Wandtemperaturen analysiert, wie sie bei Absenkung des System-druckes bzw. der Enthalpie der Strömung am Eintritt in das Versuchsrohr auftreten. Anhand der Siedekurve werden die beobachteten Wandtemperaturverläufe interpretiert. Durch Nachrechnung der Experimente mit einem dynamischen Rechen-programm lassen sich die unterschiedlichen Effekte, die während der Transiente auftreten, separieren.

---

Heat transfer in post-dryout region during transients

A change in the boundary conditions in a heated evaporator tube (moving the location of the boiling crisis downstream) could lead to a strong reduction in the heat transfer coefficient in the Post-Dryout region. The analyzed wall temperature data were obtained in a high pressure test loop by reducing the system pressure, or the enthalpy at the test section inlet. The wall temperature time histories were interpreted using the boiling curve. The various effects occurring during the transient could be separated by recalculating the tests with a dynamic simulation computer program.

---

Formelzeichen h Sättigungsenthalpie des Wassers - p Druck - p _c kritischer Druck - Q Wärmestrom - q Wärmestromdichte - q₁, q₂ Wärmestromdichte für Rohrabschnitt l bzw. 2 - t Zeit - x wirklicher Dampfmassenanteil - ¯x bilanzmäßiger Dampfmassenanteil Herrn Prof. Dr.-Ing. U. Grigull zum 70. Geburtstag gewidmet     

Ring-opening polymerizations of cyclic olefins

A ziegler-type catalyst system consisting of tungsten hexachloride and alkyl or aryl tin compounds was found to polymerize cyclopentene and other cyclic olefins through a ring-opening mechanism. This catalyst system also polymerized α-olefins such as ethylene and 1-octene. An attempt was made to copolymerize cyclopentene and ethylene. Other catalyst systems were also employed for ring-opening polymerizations with limited success.     

Heat conduction in a plane wall subject to periodic temperature changes

Analytical solutions for the heat conduction in a plane wall with periodic temperature variations at the wall surface are presented. Series and asymptotic developments of these solutions are deduced. The results are important for the calculation of the heat transfer in rotary kilns or other rotaring units.

---

Die Wärmeleitung in einer ebenen Wand mit periodischen Temperaturänderungen

Zusammenfassung Es werden analytische Lösungen für die Wärmeleitung in einer ebenen Wand mit periodischen Temperaturänderungen an ihrer Oberfläche mitgeteilt. Reihen- und asymptotische Entwicklungen dieser Lösungen werden abgeleitet. Die Ergebnisse sind wichtig für die Berechnung des Wärmetransportes in Drehrohröfen oder ähnlichen Maschinen.

---

Nomenclature a ² =/ C m²/s thermal diffusivity, Eq. (1) - C J/kg K specific heat - F K initial temperature of the wall, Eq. (4) - F m² surface of the wall - G Green's function, Eq. (10) - G₁ Green's function, Eq. (12) - h m thickness of the wall - H Heaviside function, Eq. (5) - k constant, Eq. (25) - k _x constant, Eq. (25) - Q J total energy, Eq. (17) - Q ^u J total energy from temperatureU, Eq. (18) - Q ^v J total energy from temperatureV, Eq. (19) - s s^–1 Laplace variable - t s time - t ₁ s heating time, Eq. (5) - t ₂ s period, Eq. (5) - T K temperature of the wall - T _i K surface temperature of the wall - T ₁ K surface temperature of the wall during the heating time - T ₂ K surface temperature of the wall during the cooling time - U K temperature of the wall defined in problem 1 - V, K temperature of the wall defined in problem 2 - x m coordinate - ₀ W/m²K overall heat transfer coefficient, Eq. (31) - ₁₀ W/m² K overall heat transfer coefficient, Eq. (32) - ₂₀ W/m² K overall heat transfer coefficient, Eq. (33) - Dirac Delta function - s^–1/2 parameter, Eq. (6) - W/mK thermal conductivity - kg/m³ specific mass - dimensionless time, Eq. (34) - Riemann Zeta function surfix Laplace transformed variable     

Temporal contrast control at the PHELIX petawatt laser facility by means of tunable sub-picosecond optical parametric amplification

We report on the development of a preamplifier module for temporal contrast enhancement and control at petawatt-class lasers. The module is based on an ultrafast optical parametric amplifier (uOPA), which produces temporally clean pulses at the 60 μJ level for seeding a chirped pulse amplification (CPA) system, namely the petawatt facility PHELIX. The amplifier module allows for gain reduction in the following amplifiers, resulting in an attenuation of amplified spontaneous emission (ASE) by more than 4 orders of magnitude. Since the ASE of a CPA system linearly depends on the seeding energy, we were able to demonstrate a continuous variation of the temporal contrast by tuning the gain of the uOPA.