Showing papers by "Technische Universität Darmstadt published in 1990"

Joint investigation of concrete at high rates of loading

Abstract: Uniaxial tensile tests have been carried out on a micro-concrete with strain rates between 0.5 and 1.25 s−1. The investigation is described and the results are discussed with respect to the influence of water content on the strain-rate sensitivity.

The radiobiological and physical basis for radiotherapy with protons and heavier ions.

Abstract: Heavy charged particles exhibit a superior dose distribution compared to all conventionally used beams. The small lateral and range straggling, combined with an increase of the dose deposition with increasing penetration depth enables the production of dose profiles shaped precisely to the contours of the treatment volume. In addition, heavy ion beams exhibit an elevated biological efficiency close to the end of the particle range. Therefore, beams of heavy ions deliver a high physical dose combined with a high biological efficiency to a tumor volume while the surrounding healthy tissue is maximally spared.

From pore size distribution to an equivalent pore size of cement mortar

Abstract: An experimental and theoretical study has been performed with the aim of quantifying pore size distribution curves and correlating them with water and oxygen permeability. Twenty mortars have been investigated which contained Portland cement, blast-furnace slag cement and silica fume as a binder. Admixtures have been used as well. The water-cement ratio varied between 0.4 and 0.75 and two curing conditions were applied. By the use of mercury intrusion porosimetry, the pore size distribution was determined. Water and oxygen permeability have been measured in the steady state. Equivalent pore sizes have been calculated which quantify the pore size distribution by a single number. This number is not a constant but depends on the physical transport mechanism. It is shown that equivalent pore size and porosity together are sufficient to predict the physical properties with an acceptable accuracy.

Estimation of Physical Parameters for Dynamic Processes with Application to an Industrial Robot

Abstract: The unknown parameters of physical laws which govern the dynamics of processes can be gained from measured input and output signals in a two step procedure. First the parameters of differential equations are estimated and then the physical parameters are calculated based on algebraic relations. After considering the model structures a suitable parameter estimation method for continuous time signals is described and the influence of a priori known parameters on the convergence is shown. Then the determination of physical parameters is considered based on nonlinear algebraic relations known from theoretically modeling. Applying the implicit function theorem identifiability conditions for the unique determination of physical parameters are given. Then applications are shown for the estimation of the ratios of inertia, d.c. motor damping coefficients and Coulomb friction coefficients of an 6-axis-industrial robot.

Wear behaviour of r.f.-sputtered TiN, TiB2 and Ti(B,N) coatings on metal forming tools in a model wear test

Abstract: Within the last few years grey cast iron tools have been widely used for sheet metal forming owing to their low friction coefficient and excellent emergency running properties. Low hardness values and therefore reduced abrasive wear resistance are the main restrictions for this material. As shown in previous work, TiN coatings reduce the abrasive wear of cast iron test pieces under several tribological conditions. In this paper we deal with thin hard coatings of the system Ti-B-N deposited onto cast iron by means of an r.f. sputter process with r.f.-biased substrates. The coatings were tested with regard to their fundamental properties such as hardness, adhesion and structure. The most promising TiN, TiB 2 and Ti(B,N) coatings were tested under metal forming conditions. It is shown how the graphite lamellae of grey cast iron substrates disturb the coating structure. The main wear mechanism results from cracking of the coatings in the areas of graphite lamellae. The cracking leads to highly abrasive wear debris containing hard coating and substrate particles. Therefore a 1 μm thick pure titanium layer is deposited prior to the hard coating to reduce the influence of the graphite on the growth of the hard coating. As a main result the wear behaviour of the coated tools is remarkably improved without a significant change in coating hardness or adhesion.

Study of very thin oxide layers by conversion and Auger electrons

Abstract: Oxidic layers as thin as 20–30 A on α-Fe and stainless steel are studied by57Fe-DCEMS with K-conversion electrons and ICEMS. No indication of a vanishingf-factor could be found. Mossbauer spectra, recorded by use of LMM-Auger electrons (AEMS) and by electrons emitted with energies below 15 eV (LEEMS), contain information on the surface layer as well as on the bulk material, showing that part of these electrons are due to secondary effects and the high escape depths of K-conversion electrons.

Derivation of response equations for the nondestructive probing of charge and polarization profiles

Abstract: Several experimental techniques for the nondestructive probing of charge and polarization profiles in thin dielectrics are available. Most of these methods are based either on the diffusion of heat after a thermal excitation or on the propagation of a pressure wave after mechanical excitation. A general response equation for these two families of experimental techniques is derived on the basis of a laboratory coordinate system, in which the relative movement of charges and sample electrodes is considered. Position-independent material parameters are assumed in the one-dimensional model, since unique profiles can otherwise not be determined from the experimental results; piezoelectric and pyroelectric coefficients are, however, treated as variables and may therefore be position dependent. The first-order derivation itself starts from the fact that a mechanically or thermally excited sample may be seen as a current source, since charge movement in an insulating sample always represents a current. Furthermore, because of continuity, the externally detected current equals the internal sample current. It is shown that the direct approach yields the same general response equation as an earlier rudimentary approach and that this equation can be easily adapted to the different experimental situations of the various pressure-wave and thermal-excitation methods.

Laser spectroscopy of radioactive lead and thallium isotopes

Abstract: By collincar fast beam laser spectroscopy hyperfine structure and isotope shift have been measured of neutron deficient radioactive isotopes of lead (190Pb,191Pb,192Pb,193Pb,194Pb,195Pb,196Pb,197Pb) and thallium (188Tl190Tl,191Tl,192Tl,194Tl,196Tl). Therefrom nuclear magnetic dipole moments, electric quadrupole moments, changes of the mean square charge radii and deformation parameters are deduced and compared with predictions from theory.

Pion-transfer reaction spectroscopy of inverse kinematics for studies of deeply bound pionic atoms in heavy nuclei

Abstract: A new type of nuclear reaction spectroscopy using inverse kinematics is proposed and discussed with a special emphasis on the application to charge-exchange pion-transfer reactions such as (d, 2 He) and (t, 3 He) to embed real pions onto heavy nuclei forming deeply bound pionic atoms, which were predicted by Toki and Yamazaki to have narrow widths due to the repulsive strong-interaction potential. A typical case considered is to use heavy-ion projectiles of 400 MeV/u range on a light target such as d or t and to measure the recoil particles of low-energy range corresponding to forward scattering. The recoil momentum is shown to be nearly equal to the Lorentz-invariant momentum transfer of the reaction, typically, around 140 MeV/ c , which is proportional to the excitation energy. Compared to the conventional method, the present inverse-kinematics one not only provides a better energy resolution (around 100 keV at 140 MeV excitation) but also permits studies of π − bound states on unstable nuclei, hitherto unconceivable objects for spectroscopy. Some experimental configurations to be used in a cooled circulating beam are discussed.

Local aggregation in a dynamic setting

Abstract: Although it is not possible, in general, to give a macro description of a micro model over the entire state space of the micro model, it is possible to aggregate exactly over a subspace. The set of micro states where aggregation is possible forms the aggregation set. The paper considers the local (linear) case. The macro model is chosen such that it gives rise to an aggregation set which is approached by the micro movements as fast as possible. The inferred macro model describes trajectories of the aggregate quantities towards which the "true" trajectories of these quantities, as generated by the micro model, are tending.

Triaxiality andγ-softness in196Pt

Abstract: The nuclear level structure and electromagnetic properties of196Pt were investigated withγ-spectroscopic techniques using multiple Coulomb excitation by208Pb projectiles. Particle-γ, and particle-γ-γ coincidences were measured over a wide range of scattering angles.E2-transition moments and static quadrupole moments have been determined by a comparison of experimental scattering-angle dependentγ yields with calculated yields in a largely model-independent procedure. The results are compared with different theoretical models: the Asymmetric-Rotor Model, the Generalized Collective Model, and the Interacting Boson Model. The best agreement is obtained with the Generalized Collective Model representing a triaxial nucleus which is soft in theγ degree of freedom.

Fundamental and tribological properties of R.F.-sputtered TiN coatings in plastic manufacturing model wear tests

Abstract: In plastic manufacturing an increasing content of abrasive particles and corrosive components in combination with working temperatures up to 450 °C have led to a new dimension of wear. As shown in previous work, TiN coatings have been wear resistant under corrosive conditions and elevated temperatures. In this paper we deal with thin hard TiN coatings deposited onto steel substrates by means of an r.f. sputter process with r.f. substrate bias. The coatings were tested with regard to their fundamental properties such as hardness, adhesion and structure. An increased substrate bias voltage up to —100 V leads to higher hardness values and a more dense coating structure. Adhesion and cohesion of the coatings are best in the range from —30 V to —50 V. The wear behaviour of the coatings under plastic manufacturing conditions was investigated by two model wear tests. Corresponding to the conveying and the melting zones of screw barrel systems the test pieces were subject to abrasive and abrasive-corrosive wear under elevated temperatures. It is shown that the combination of high hardness, dense structure and good adhesion leads to superior wear behaviour of r.f. bias sputtered TiN coatings. For the melting zone model wear test a remarkable improvement in wear resistance by a factor of more than 10 was achieved.

Local Aggregation in a Dynamic Setting

Abstract: Although it is not possible, in general, to give a macro description of a micro model over the entire state space of the micro model, it is possible to aggregate exactly over a subspace The set of micro states where aggregation is possible forms the aggregation set The paper considers the local (linear) case The macro model is chosen such that it gives rise to an aggregation set which is approached by the micro movements as fast as possible The inferred macro model describes trajectories of the aggregate quantities towards which the "true" trajectories of these quantities, as generated by the micro model, are tending

Photofission of 238U with monochromatic gamma rays in the energy range 11-16 MeV.

Abstract: We have measured the angular and mass distributions of the fragments from photofission of {sup 238}U using tagged photons with energies between 11 and 16 MeV. The fission fragments were detected by a 4{pi} arrangement of position-sensitive parallel-plate avalanche counters. Anisotropic angular distributions have been observed for the first time in the energy range where second-chance fission becomes energetically possible. A consistent assignment of {ital J}{sup {pi}} and {ital K} for the fission channels in {sup 237}U has been deduced from a combined analysis of ({gamma},{ital nf}) and ({ital e},{ital e}{prime}{ital f}) data. A clear relationship between the anisotropies and the fragment mass asymmetry has also been established. This correlation, together with the energy dependence of the angular distribution parameters, points to a possible interpretation of the results in terms of a recent theoretical model incorporating multiple exit channels in fission.

Use of computer-based factory automation (CBFA) in West German companies

Abstract: The traditional 'hard' automation in manufacturing is being replaced more and more by ‘soft’, computer-based automation equipment (CAD, CAP, CAM, CAQ, and PPS). A recent survey in the West German machine building and equipment manufacturing industry shows that many companies use new manufacturing technologies. Although the report revealed that small companies have been using computer-based factory automation (CBFA) technologies for a shorter time, their frequency in using these technologies is nearly the same as in large companies. The application rates still signal high potentials for further CBFA and its benefits to enhance the performance in quality, time, and cost of manufacturing.

Timing Driven Partitioning of Combinational Logic

Abstract: This paper presents a new approach to timing driven partitioning of combinational logic. Instead of accessing a predefined library, complex gates based on the line-of-diffusion layout style are automatically generated, placed and routed. A new timing model for complex gates is discussed which permits a fast pattern independent timing analysis with a deviation of less than 15% and two to three orders of magnitude faster than the exact SPICE simulation taking into account all parasitics and signal arrival times. A new partitioning technique for complex gates is presented to improve the timing behaviour.

Einleitung zum ersten Band

Abstract: Die Hochfrequenztechnik verwendet elektrische Wechselstrome, -spannungen und -felder mit Frequenzen zwischen etwa 3 kHz und etwa 1 PHz (1 Petahertz = 1015 Hz), die also uber fast 12 Zehnerpotenzen reichen. Diese Grenzangaben enthalten naturlich eine gewisse Willkur. Ein Grundsatz der Hochfrequenztechnik ist, das die Frequenz des Nachrichtentragers hoher ist als die der Nachricht. Gegenuber der Frequenz von Morsezeichen oder Fernschreiberzeichen ist 3 kHz eine hohe Frequenz.