Showing papers by "Technische Universität Darmstadt published in 1991"

Carbohydrates as organic raw materials.

Abstract: In view of the impending transition of chemical industry from depleting fossil raw materials to renewable feedstocks — the end of cheap oil is predicted around 2040 — this account gives an overview on chemically and enzymatically transforming carbohydrates, by far the major part of the annually regrowing biomass, into products with versatile industrial application profiles and the potential to eventually replace those presently derived from petrochemical sources. The article contains sections titled: 1. Introduction 2. Availability of Carbohydrates 3. Current Nonfood Industrial Products from Sugars 3.1. Ethanol 3.2. Furfural 3.3 d-Sorbitol 3.4 Lactic Acid and Polylactic Acid (PLA) 3.5. Sugar-Based Surfactants 3.5.1. ‘Sorbitan’ Esters 3.5.2. N-Methyl-N-acyl-glucamides (NMCA) 3.5.3. Alkylpolyglucosides (APG) 3.5.4. Sucrose Fatty Acid Monoesters 3.6. Pharmaceuticals and Vitamins 4. Toward Further Sugar-based Chemicals: Potential Development Lines 4.1. Furan Compounds 4.1.1. 5-Hydroxymethylfurfural (HMF) 4.1.2. 2,5-Dimethylfuran (DMF) 4.1.3. Furans with a Tetrahydroxybutyl Side Chain 4.2. Dihydropyrones 4.3. Sugar-Derived Unsaturated Nitrogen Heterocycles 4.3.1. Pyrroles 4.3.2. Pyrazoles 4.3.3. Imidazoles 4.3.4. 3-Pyridinols 4.4. Toward Sugar-Based Aromatic Chemicals 4.5. Microbial Conversion of Six-Carbon-Sugars into Simple Carboxylic Acids and Alcohols 4.5.1. Carboxylic Acids 4.5.2. Potential Sugar-Based Alcohol Commodities by Microbial Conversions 4.6. Chemical Conversion of Sugars into Carboxylic Acids 4.7. Biopolymers from Polymerizable Sugar Derivatives 4.7.1. Synthetic Biopolyesters 4.7.2. Microbial Polyesters 4.7.3. Polyamides 5. Outlook 6. References

Corrosion performance of some titanium-based hard coatings

Abstract: Tools and machine parts which could benefit from wear-resistant titanium-based hard films are often subject to corrosive environments. Physically vapour-deposited coatings frequently exhibit porosity and even small defects, which can cause rapid local corrosion of the substrate material; there is therefore a requirement for dense and chemically inert coatings. This paper presents corrosion data for titanium-based hard coatings such as TiN, (Ti,Al)N, Ti(B, N) and TiB2 and also for multilayered structures where additional aluminium-based insulating surface layers (AlN and Al2O3) were deposited. The corrosion resistance and porosity of the films were analysed by electrochemical techniques. The degree of metallic bonding can play a significant role in influencing the corrosion resistance of refractory transition-metal-based ceramic coatings. Here we demonstrate that, under potentiodynamic corrosion test conditions, resistance to corrosive attack was relatively poor for TiB2, better for (Ti, Al)N and Ti(B, N) and best for TiN. It is also shown that applying the additional protective aluminium-based insulating surface layers on the coating can further improve corrosion resistance.

Fragmentation of gold projectiles: From evaporation to total disassembly

Abstract: We have studied the fragmentation of Au projectiles interacting with targets of C, Al and Cu at an incident energy ofE/A=600 MeV. The employed inverse kinematics allowed a nearly complete detection of projectile fragments with chargeZ≧2. The recorded fragmentation events were sorted according to three observables, the multiplicityMlp of light charged particles, the largest atomic numberZmax within an event, and a new observable,Zbound, representing the sum of the atomic numbersZ of all fragments withZ≧2. Using these observables, the impact parameter dependence of the fragmentation process was investigated. For all three targets, a maximum mean multiplicity of 3 to 4 intermediate mass fragments (IMFs) is observed. The corresponding impact parameters range from central collisions for theC target to increasingly peripheral collisions for the heavier targets. It is found that the correlation between the IMF multiplicity andZbound, extending from evaporation type processes (largeZbound) to the total disassembly of the projectile (smallZbound), is independent of the target nucleus. This universal behaviour may suggest an — at least partial — equilibration of the projectile fragment prior to its decay.

Fundamental properties and wear resistance of r.f.-sputtered TiB2 and Ti(B,N) coatings

Abstract: Thin films of TiB2 and Ti(B,N) were deposited by means of r.f. sputtering. Fundamental properties such as structure, adhesion, hardness and internal stresses were determined as a function of the deposition parameters. By systematically changing the substrate voltage and in the case of Ti(B,N) the nitrogen flow, the film properties could be influenced over a wide range. The coatings have been tested with regard to their tribological behaviour by means of a model wear-testing apparatus. It is shown that Ti(B,N) is a promising coating for wear protection.

Breakdown of the compound-nucleus model in the fusion-evaporation process for 110 Pd+ 110 Pd

Abstract: The fusion of the massive systems110Pd+104Ru and110Pd+110Pd was uniquely identified by observing the a decay of the evaporation residues. The observed distribution of the fusion cross section on the different evaporation-residue channels is in clear contradiction to calculations based on the compound-nucleus model. As a possible explanation the precompound evaporation of a particles is proposed.

Phase equilibria in the system poly(ethylene glycol) + dextran + water

Abstract: The lines in the system poly(ethylene glycol) 3000+dextran 500 000+water have been measured at 0, 20, and 40 o C. The concentration and molecular weight distributions of the polymers in coexisting liquid phases were determined by using size exclusion chromatography (SEC)

Multiwire chambers with a two-stage gas amplification

Abstract: Some unique features of multistep avalanche chambers are investigated. This type of chamber is very well suited for the analysis of thin-layer radiochromatograms (labeled with 3 H, 14 C or 32 P). A resolution of 0.5 mm FWHM in the two coordinates is routinely achieved.

Results on two-, three-, and four-body events from the 100 Mo+ 100 Mo and 120 Sn+ 120 Sn collisions around E/A =20 MeV

Abstract: Events with 2, 3 and 4 heavy-fragments (A≧20) have been detected in the reactions100Mo+100Mo atE/A =18.7, 23.7 MeV and120Sn+120Sn atE/A=18.4 MeV. The experiments were performed with an array of 12 detectors which together covered a large fraction of the forward hemisphere and allowed a high detection efficiency for these events. Masses and energies of all fragments have been reconstructed by means of an improved version of the kinematic coincidence method. The probabilitiesP 3 andP 4 of producing 3- and 4-body events were found to depend mainly on the dissipated energy rather than on the bombarding energy, thus indicating that their origin lies more in the decay properties of the excited fragments than in the dynamics of the interaction. Emission of light particles from the composite system is shown to become more relevant with increasing bombarding energy and may explain the drop of theP 3 andP 4 curves at high energy losses. Small deviations of theP 3 andP 4 curves at 23.7A · MeV from those at lower bombarding energies were used to estimate the amount of a possible pre-equilibrium light particle emission as a function of impact parameter.

Tribological properties and wear behaviour of sputtered titanium-based hard coatings under sheet-metal-forming conditions

Abstract: In recent years, grey cast iron tools have been widely used for sheet metal forming because of their low friction coefficient and excellent emergency running properties. Low hardness and therefore reduced wear resistance are the main restrictions for this material. Tool steels are harder, but against steel workpiece material a tendency to adhesive wear might cause problems under insufficient lubrication. As shown in previous work, TiN coatings reduce the abrasive and adhesive wear of cast iron and steel samples under several tribological conditions. The present paper deals with thin hard coatings within the system TiBN, deposited on grey cast iron and tool steel by means of a d.c. or r.f. sputter process with r.f.-biased substrates. The coatings were analysed with regard to their fundamental properties such as hardness, adhesion and structure. The most promising titanium-based hard coatings were tested in a tribological model wear test and under metal-forming conditions. For the grey cast iron tools it is shown how the graphite lamellae disturb the coating structure. In this case the main wear mechanism is cracking of the coatings in the areas of graphite lamellae. The cracking leads to highly abrasive wear debris containing hard coating and substrate particles. The influence of the graphite on the coating growth can be suppressed by means of a thin pure titanium layer deposited prior to the hard coating. As the main result the wear behaviour of the coated grey cast iron tools is remarkably improved without a significant change in coating hardness or adhesion. On steel tools no influence of the base material on the coating was observed. For the coating a low tendency of adhesion to the workpiece material and high hardness values were obtained as well, which leads to a superior wear resistance of coated steel tools under sheet-metal-forming conditions.

The branching ratio of β-delayed two-proton emission

Abstract: The decay of theβ +-fed isobaric analog state by one- and two-proton emission is calculated in the formalism of compound-nucleus decay. Support is given to the uncorrelated character of the emitted protons in theβ2p process. The ratio ofβ2p toβp probabilities is obtained for the isotopes predicted to beβ2p emitters up to Z=30, i.e.22Al,22,23Si,26P,27S,31Ar,35Ca,39Ti,43Cr,46Mn,46,47Fe,49–51Ni, and55Zn.

Neutral meson production in relativistic heavy ion collisions

Abstract: The production of pi-0 and eta-mesons has been studied in the reactions Ne-20 + Al at 350 MeV/u and Ar-40 + Ca at 1.0 GeV/u. Rapidity distributions and transverse momentum spectra have been measured and are compared to thermal distributions.

Absorption of carbon monoxide, hydrogen, and methane in toluene and copper(I) tetrachloroaluminate-toluene solutions at elevated pressures

Abstract: Solubilities of the coal-gasification products CO, H 2 , and CH 4 in pure toluene have been measured at temperatures between 249 and 343 K and pressures up to 7 MPa. Phase equilibria of CO and copper(I) tetrachloroaluminate-toluene solutions are presented between 254 and 333 K and pressures up to 9.5 MPa. In this absorbent, reversible chemical reactions occur resulting in a formation of several bimetallic salt complexes having a high bonding capacity for CO. Solubility measurements with H 2 and CH 4 in this agent show that these gases do not undergo any chemical reaction

RAMSES-a rapid prototyping environment for embedded control applications

Abstract: An environment is given for fast prototyping of real-time systems. The supported spectrum of realizations for such systems varies from single task implementations on a general purpose microprocessor to heterogeneous multiprocessor systems with application specific processors. The prototyping environment includes a language to describe a real-time system, a compiler that transforms the description into its specified realization format and a hardware environment that is based on a VMEbus system. The VMEbus system includes a Motorola 68020 CPU with multi-tasking operating system and a prototyping board which can be either configured as multi-DSP board or as emulation board for the implementation of an application specific processor architecture. >

Automatic performance characterization of analog functional blocks

Abstract: Performance analysis based on simulated results is a fundamental task of integrated circuit design. An approach to automated performance characterization of analog and mixed mode functional blocks is presented. The key points of this approach are an introduction of a procedural simulation method and a dedicated programming language for its implementation. Starting from a structural description of a building block and a set of specifications on its operational conditions the proposed method supports the generation of a comprehensive set of electrical properties, whereas no restrictions on underlying fabrication technologies or application domains of the circuit have to be taken into account. The flexibility of the proposed approach is demonstrated for two circuit examples, which differ both in their fabrication technology and in their application areas.

VLSI System Design for automotive Control

Abstract: This paper presents a novel VLSI approach for combustion engine control. The approach is based on a real time solution of a thermodynamical differential equation. The control system calculates an optimum ignition point by fast measurement and real time processing of signals as temperature, pressure and volume of the combustion chamber. The required computational power cannot be met with standard signal processors. We present the design of a mechatronic system that is based on an application specific vector architecture. The optimization of the algorithm and the dataformat, the mapping on an architecture, the physical design of the VLSI chip set, the test results, and the system integration are shown.

Large electron polarization of H-like20Ne-ions traversing gd foils at very high velocities

Abstract: It is shown that transient magnetic fields in Gd-host for20Ne ions at a mean velocity of 12.5v0(v0=c/137), considerably beyond the Bohr velocity of 1s electrons of Ne ions (v1s=10v0), are dominated by the Fermi contact field of these electrons. The first excited 2+-state of2Ne was used as probe. The derived value for the mean degree of polarization p1s=0.32(13), is surprisingly large, though still consistent with values obtained at lower velocities. Present calculations of spin exchange cross sections severely underestimate the observed polarization at this high velocity.

HADES-high-level architecture development and exploration system

Abstract: The authors propose a new approach to high level behavioural synthesis starting from an algorithmic description in Hardware C. The algorithm is compiled into a corresponding data/control flow graph including several optimizations. The behavioural synthesis part of the system performs transformations like loop unrolling, parallelization, etc., whereby the user is supported through a feedback loop. For final structural synthesis an advanced tool based on genetic algorithms is provided. Layout synthesis is assumed to be performed by available tools like the GENESIL silicon compiler. >

A VLSI implementation of a state variable filter algorithm

Abstract: The authors present a digital signal processor (DSP) architecture whose powerful CPU is optimized to solve a state variable filter algorithm, but is not limited to that application. State variable filters perform low pass filtering and generate the derivatives of the filtered signal. These signals are used in systems for real-time process identification. In order to minimize the number of components, program and data memory, timers, and peripheral control logic are integrated on the DSP chip. Software development for this DSP is supported by an assembler, simulator and high level language compiler. In addition to the presentation of the architecture, a design methodology is introduced which uses rapid prototyping techniques to verify system design and algorithms in their real-time environment. >

An Approach to the Application of Dedicated Neural Network Hardware for Real Time Image Compression

Abstract: Image processing is a demanding task where classical systems face nearly insurmountable problems forcing the application of dedicated hardware. In this paper the application of a binary neural network for image compression by means of vector quantization is proposed. Data compression has been carried out on video phone images using a binary associative memory in conjunction with simple data preprocessing, simulated on a sequential computer. A cascadable VLSI-Implementation of the network has been developed at DUT and is available making a hardware realization feasible. The codebook for vector quantization has been generated by a classical algorithm, as well as by the application of a self-organizing neural network, the Kohonen Feature Map. Results achieved with the latter were most encouraging.

A CAD tool for designing large, fault-tolerant VLSI arrays

Abstract: The authors describe implementation details of a CAD tool for efficient hardware realization of highly parallel algorithms. The Array Specification Language (ASL) of the tool allows the VLSI designer to specify the input not only at dependence graph level, but also at signal/data flow graph and/or array architecture level. Core of this tool is a multilevel functional-structural simulator, embedded into an environment supporting array processor design for real world applications. Another aspect of the tool is the intended support of advanced fault tolerance techniques in an early design phase. More emphasis is given to fabrication-time/run-time fault tolerance techniques and to find a cost-effective solution with the evaluation of optimality criteria and real design tradeoff. >

Response functions of Si detectors to monoenergetic electrons and positrons in the energy range 0.8–3.5 MeV☆

Abstract: The response functions of Si surface barrier detectors (depletion depth: 2 mm, active area: 200 mm 2 ) to monoenergetic electrons and positrons have been measured in the energy range 0.8–3.5 MeV at the Giessen electron linear accelerator. Lower peak-to-total ratios were observed in the positron response functions compared to electrons. The measured response functions were compared with Monte Carlo simulations enabling a separation of the individual contributions to the response function such as: total energy loss, backscattering, transmission, bremsstrahlung emission. A parametrization of the response function for electrons is given, which allows a reliable approximation of the response function in the investigated energy range.