Showing papers by "Technische Universität Darmstadt published in 1985"

The isotopes 259 106, 260 106, and 261 106

Abstract: In irradiations of207Pb and208Pb, respectively, with54Cr theα-decay of the isotopes259106,260106, and261106 could be observed for the first time. For260106 a spontaneous fission branch of (50 −20 +30 )% was observed. The isotopes were identified by genetic relationships of α-decay after separation in-flight with the velocity filter SHIP and implantation into a position-sensitive silicon surface-barrier detector. The measured partial fission halflife of the doubly even isotope260106 of (7.2 −2.7 +4.8 )ms exceeds the predicted values by at least a factor of 40. This result could be explained by the high shell corrections of the ground state mass, derived from the measured α-decay energies. The experimental results show evidence for an island of purely shell stabilized nuclei in the region of deformed isotopes beyond the actinides.

Scalarization in Multi Objective Optimization

Abstract: In this paper general multi objective optimization problems are investigated for different optimality notions. For these problems appropriate single objective optimization problems are presented whose optimal solutions are also optimal for the multi objective optimization problem. And conversely, for optimal solutions of a multi objective optimization problem suitable single objective optimization problems are considered which have the same optima. These results lead even to a complete characterization of the optimal solutions of multi objective optimization problems. Finally, this theory is applied to vector approximation problems.

High-spin isomers in W and Os nuclei; Competition betweenK-quantization and triaxiality

Abstract: Results of a search for high-spin isomers in W and Os nuclei withN=104–107 are presented. Targets of48Ca and48, 50Ti are bombarded with a pulsed136Xe beam, and delayed gamma-radiation is detected by an array of NaI- and Ge-detectors. Several new isomers, with spin values up to ∼22h, are found in178,180W and180, 182, 183Os. Markedly different decay patterns and hindrance factors are found in the Os isotopes as compared to the expectations based on theK-selection rule valid for axially symmetric nuclei. The findings are ascribed to the onset of triaxial distortions.

Stylopid larva from the Eocene: a spotlight on the phylogeny of the Stylopids (Strepsiptera)

Abstract: A fossil insect from the Eocene brown coal of Halle-an-der-Saale (German Democratic Republic), Pseudococcites eocaenicus Haupt 1950, misidentified by its describer as a species of Coccoidea, was re-examined and re-identified as a primary larva of twisted winged insects (Strepsiptera: Myrmecolacidae: Stichotrema ) and re-named Stichotrema eocaenicum (Haupt 1950). To date, this is the oldest fossil record of Strepsiptera

A Simple Method for Automatic Tuning of PID-Controllers based on Process Parameter Estimation

Abstract: Microprocessor-based tuning aids and self-tuning-methods for conventional PID-controllers are an important subject to industrial users. Some of the existing techniques use simple pattern-recognition, some use expensive optimization procedures. This paper describes a simple self-tuning-procedure for PI- and PID-controllers, which is based on discrete parameter estimation and application of slightly modified Ziegler-Nichols tuning-rules. Controller tuning has been simplified to the choice of the desired over-shoot of the PID-controlled closed loop system. The method is easy to implement in microprocessors and allows quick online-tuning of PID-controllers. Simulation results and a comparison with controllers tuned by an optimization procedure are presented.

Surface charging of dielectrics by secondary emission and determination of emission yield

Abstract: A new method for the determination of the secondary emission yield of dielectrics is discussed. Results are given for Teflon, Aclar, Kapton, and Mylar. Surfaces of dielectrics irradiated with electrons of energies above 2 keV become negatively charged. For lower energies the number of back-scattered primaries plus backward emitted secondaries eventually exceeds that of the incoming primaries. Then the surface can be positively charged [1]. It was recognized that this effect might lead to a simple method for the determination of the total backscatter plus secondary emission yield [2]. This effect is used to determine the total emission yield curve in one run with a single beam energy.

Charge and polarization profiles in polymer electrets

Abstract: Laser-induced pressure pulses (LIPP's) of < 500 ps duration have been used to measure the ultrasonic attenuation in fluoroethylenepropylene (FEP), polyethyleneterephthalate (PETP) and polyimide (PI) as well as the charge, polarization, and piezoelectricity profiles in the thickness direction of polyvinylidenefluoride (PVDF) and FEP electrets with a resolution of 1 to 2 μm. Measurements on PVDF, obtained during and after poling, reveal a uniform polarization profile for samples poled at room temperature and a non-uniform polarization, concentrated near the positive electrode, for samples poled at elevated temperatures. In FEP, charges injected by electron beams are stored close to the CSDA range while negative carriers deposited by corona discharges or liquid-contact electrodes are trapped at, or close to, the surface.

Breakdown Voltage of Conditioned 24 kV-Vacuum Tubes as a Function of Ramp Rate

Abstract: For the determination of the dielectric strength of different factory-made vacuum interrupter tubes, in the short time range, the breakdown voltage was measured as a function of the voltage ramp rate for various contact distances by applying linear rising impulse voltage with a steepness from 1 kV/ ?s up to 3 MV/ ?s. Preconditioning of the contacts was performed with a series of impulse breakdowns. An impulse voltage measuring circuit with a damped capacitive voltage divider and damped lead-in wire was used for the investigations. Adequate steps were taken to avoid flashovers outside the tubes and to give protection against X-rays. After preconditioning, g, some vacuum tubes reached a maximum dielectric strength of 550 kV at the rated contact distance of 14 mm. The minimum values were about 120 kV. The shape of the voltage ramp curves, which is dependent on the contact distance, leads to a conclusion on the effective breakdown mechanisms.

Electromagnetic probes of nuclear collisions at intermediate energy

Abstract: We show that emission of high-energy electrons and photons in nuclear collisions at intermediate energies is sensitive to the space-time evolution of the reaction. The electron and photon spectra measure related but complementary quantities connected with the nuclear charge distribution. We show that at 60 MeV/u beam energy production of 50 MeV electrons is predicted to measurable probability.

Electret research — Stages in its development

Abstract: This paper describes aspects of research on dielectrics and electrets carried out by the author over the last 50 years, in an attempt to show the systematics of its development and the logical relation between its successive steps. Starting with dielectric absorption, it covers open-circuit behavior of dielectrics, thermally stimulated currents, Paschen breakdown and its effects on the performance of the induction plate method, and the superposition of free surface charge and dielectric volume polarisation. The two-charge theory appears as the result of a straightforward application of the basic charge and field equations of electrostatics, without the introduction of a specific model. Theoretical results are developed on hand of simple experiments most of them performed with Carnauba wax. Recent research has added a wealth of detailed information, but still leaves open many important questions.

Introduction to a Simple But Unconventional Multiprocessor System and Outline of an Application

Abstract: The smaller and the cheaper microprocessors become the more tempting is it to step back from high-speed and high-power single processors and make use of multi(micro)processor systems instead.