Showing papers by "Braunschweig University of Technology published in 1986"

Computer-Aided Measurement of Relative Retardations in Plane Photoelasticity

Abstract: Computer-aided methods for evaluation of photoelastic patterns use video technique and digital image processing. They are based on localization of fringe centers [ 1, 2, 3, 4]. Neighbourhood operations are needed to reduce the influence of nonuniform illumination, inhomogeneous optical components and models, etc. Fractional orders of the relative retardation and of the isoclinic parameter at points between the fringes are computed by spline- functions, if the components of the plane stress state have to be derived from photoelastic data. In the following a method is proposed, which enables the complete extraction of photoelastic information at local picture elements (pixel) from series of related images of the same stress state. For this purpose the well-established phase-shifting technique (see e. g. [ 5,6]) was modified to meet the special requirements of photoelastic patterns.

Microprocessor-Controlled AC-Servo Drives with Synchronous or Induction Motors: Which is Preferable?

Abstract: With the recent advances of power transistors and microprocessors it has become possible to design high-dynamic-performance ac-servo drives free of moving contacts using synchronous or asynchronous motors. Both schemes have their particular strengths. A general control principle, based on field or rotor orientation, is described which has been realized with a state-of-the-art microcomputer, where all the signal processing, including modulation of the inverter, is performed by software. Extensive tests have been carried out with different motors to compare the characteristics of the various types of drives.

New OTA-capacitor realisation of a universal biquad

Abstract: An active universal biquad built with operational-transconductance amplifiers (OTAs) is introduced. In addition to the OTAs only capacitors are required as passive devices. With the help of adjustable transconductances the set of filter parameters can be varied within a wide range.

The Misorientation Distribution Function

Abstract: The analysis of misorientations has up to now usually be carried out by comparing the values obtained experimentally using two dimensional distributions of rotation axes or rotation angles with the distribution calculated by Mackenzie for the statistically random case. In this paper the presentation of the distribution of the misorientations is based on the three dimensional orientation distribution function (ODF) (as described by Bunge). The new function is termed the misorientation distribution function (MDF) to differentiate it from the ODF. The advantages in using this function are presented and illustrated by three MDF's derived from the work of Haessner, Pospiech and Sztwiertnia.

Curvature continuous curves and surfaces

Abstract: The well-known construction of the Bezier points of a cubic spline curve or surface is generalized to curvature continuous curves and surfaces. Special examples of this kind of new splines are Nu-splines and Beta-splines.

Optimization and preliminary characterization of an exopolysaccharide synthezised by Enterobacter sakazakii

Abstract: A new isolated bacterium, identified asEnterobacter sakazakii, produces a highly viscous, anionic heteropolysaccharide. Optimum conditions for production, preliminary results about the composition and also comparative rheological measurements with xanthan andA. viscosus-polysaccharide are described.

Temperature dependence of mean molecular polarizability of gas molecules

Abstract: The temperature dependence of the mean molecular polarizability of the gases He, Ar, H2, N2, O2 and C(CH3)4 has been investigated experimentally with precise interferometric measurements in the temperature range 208 K ⩽ T ⩽ 365 K. In all cases an increase of the polarizability with increasing temperature was observed. By use of the noble gases He and Ar as internal standards it is possible to derive a relation between our results and the simple theory of Bell [1].

Energy distributions of neutral atoms sputtered from Cu, V and Nb under different bombardment and ejection angles

Abstract: The energy distributions of neutral atoms sputtered from clean polycrystalline metals (Cu, V, Nb) have been measured for different combinations of the angle of incidence θi of the bombarding Ar+ ions and the ejection angle θc (θi/θc=0°/0°, 20°/70°, 70°/20° and 45°/45°), and for bombarding energies of 0.6, 1.0 and 2.0 keV. For oblique bombarding and ejection angles the measured energy distributions show significant deviations from the well known E/(E+U0)3 formula. This is discussed with regard to the incomplete development of the sputtering cascades.

Formation of cellobiose lipids by growing and resting cells of Ustilago maydis

Abstract: Utilizing coconut oilUstilago maydis ATCC 14826 synthesizes cellobiose lipids under N-limitation conditions and as resting cells, which gave the highest specific biosurfactant production (0.79 g/g substrate). C6-, C12-, C14-, and 15, 16-dihydroxy-C16-fatty acids are the main components of the lipophilic moiety of these glycolipids.

Transferable parameterization methods for distributed hydrological and agroecological catchment models

Abstract: Summary The application of distributed hydrological and agroecological models requires the knowledge of model parameters, boundary conditions and initial conditions for each element of the three-dimensional finite difference grid in the catchment area under survey. This paper discusses methods suitable for processing the values of such parameters. The Digital Relief Model can be used to compute the ecologically relevant morphographic parameters for any point in the catchment, e.g. drainage direction, curvature, size of the drainage area above this point, distance from divide and drainage channel. The three-dimensional Digital Sediment and Soil Model determines the thickness of sediments and soil horizons as well as the parameters describing the sediments and soils (e.g. texture, structure, humus content) for any chosen site. The Land Use Data Processor computes data from maps, and remote sensing data (e.g. direction of tillage, height and density of plants) and makes these data available in any chosen grid. Only a limited number of measurements of the soil moisture suction, the soil moisture contents and the groundwater level will be necessary to derive a spatial distribution of these values on account of relatively close relations to relief and sediment parameters determined by the Digital Relief, and the Digital Sediment and Soil Models.

The problems of language control: Editing, monitoring, and feedback*

Abstract: The incorporation of editors and monitors in models of language production has become a common practice over the past ten years or so. However, there is much confusion in the psycholinguistics literature about these two control mechanisms. A monitor is redefined as a television viewer who can spot problems on the screen but cannot do anything about it. An editor, in contrast, is powerful enough to change the programme so as to produce fewer and less anomalous errors. Although there is no doubt that our speech is internally monitored, it is far from clear that this is achieved via editing. Not only can editing models be shown to suffer from serious defects, but also the data which motivated the introduction of editors in the first place lend themselves more plausibly to a reanalysis in terms of evidencing properties of the regular programming process. It is argued that McClelland and Rumelhart's interactive activation model accommodates the monitoring function quite nicely without any additional theoretical apparatus. Monitoring is carried out by a mechanism called non-local feedback which results automatically from bottom-up information flow in a parallel processing system. All the speaker has to do is to check the activation levels of the nodes in his internal network. He discovers problems whenever the levels of activation are too low with respect to the idea he wishes to communicate.

New equipment for the scaled up production of small spherical biocatalysts

Abstract: A new apparatus with a capacity up to 24 kg per hour for physical entrapment of cell fragments or whole cells in polymeric networks was constructed, based on a high speed rotating nozzle-ring. Immobilized biocatalysts are prepared at laboratory scale with bead size under 1 mm diameter, with a deviation of 10 % or less in size distribution.

Selective uptake of pyrrolizidine N-oxides by cell suspension cultures from pyrrolizidine alkaloid producing plants

Abstract: The N-oxides of pyrrolizidine alkaloids such as senecionine or monocrotaline are rapidly taken up and accumulated by cell suspension cultures obtained from plants known to produce pyrrolizidines, i.e. Senecio vernalis, vulgaris, viscosus (Asteraceae) and Symphytum officinale (Boraginaceae). The transport of the N-oxides into the cells is a specific and selective process. Other alkaloid N-oxides such as sparteine N-oxide are not taken up. Cell cultures from plant species which do not synthesize pyrrolizidine alkaloids are unable to accumulate pyrrolizidine N-oxides. The suitability of the pyrrolizidine N-oxides in alkaloid storage and accumulation is emphasized.

Plasma Waves Associated with the First AMPTE Magnetotail Barium Release.

Abstract: Plasma waves observed during the March 21, 1985, AMPTE magnetotail barium release are described. Electron plasma oscillations provided local measurements of the plasma density during both the expansion and decay phases. Immediately after the explosion, the electron density reached a peak of about 400,000/cu cm, and then started decreasing approximately as t to the -2.4 as the cloud expanded. About 6 minutes after the explosion, the electron density suddenly began to increase, reached a secondary peak of about 240/cu cm, and then slowly decayed down to the preevent level over a period of about 15 minutes. The density increase is believed to be caused by the collapse of the ion cloud into the diamagnetic cavity created by the initial expansion. The plasma wave intensities observed during the entire event were quite low. In the diamagnetic cavity, electrostatic emissions were observed near the barium ion plasma frequency, and in another band at lower frequencies. A broadband burst of electrostatic noise was also observed at the boundary of the diamagnetic cavity. Except for electron plasma oscillations, no significant wave activity was observed outside of the diamagnetic cavity.

Curve fitting algorithm for rough cutting

Abstract: This paper is concerned with the problem of fitting a continuous parametric curve to erroneous data obtained from the rough cutting procedure. The curve consists of circular arcs and straight line segments and the algorithm relies merely on elementary circle geometry.

Velocity and sediment concentration fields across surf zones

Abstract: Wave-induced currents and sediment concentrations in suspension across the surf zone were investigated at prototype scale in the BIG WAVE FLUME in Hannover for combined beach and dune profiles as well during the development phase until quasi-equilibrium stage as after beach equilibrium conditions had been reached. The selected initial profiles were partly investigated in repeated tests with regular and irregular waves. Based upon the obtained experimental data a comparison is presented between the measured and calculated landward displacement of sediment volume through a selected point on the beach into seaward areas. The discrepancies in between the results for measured profile change and for calculated sediment transport volume derived from vertical current and suspension distributions are discussed.

Subjective stress sensitivity and physiological responses to an aversive auditory stimulus in migraine and control subjects.

Abstract: Subjective stress sensitivity and physiological parameters were compared between 24 migraine subjects and 24 matched headache-free controls during a multifrequency 85-dB (A) aversive auditory Stressor and during a recovery period. Measures consisted of frontalis EMG, temporal artery blood volume pulse, heart rate, a stress sensitivity questionnaire, stress reaction during the stress-expectation period, and ratings of noise aversiveness. Migraine subjects showed a higher level of general stress sensitivity, increased situational stress sensitivity, and higher ratings of noise aversiveness; this supports the general notion that migraine sufferers are psychologically more sensitive toward stress stimulation than nonheadache controls. Physiologically, the migraine subjects differed from the control group only with regard to the temporal blood volume pulse during stress stimulation; this finding is consistent with Wolff's weak-link theory.

A new genetic model for the North African metasomatic siderite deposits

Abstract: Based on published accounts of the diagenetic evolution of evaporite diapirs and geological, preliminary geochemical, and fluid inclusion data a new genetic model is presented for the North African metasomatic siderite deposits.

(R)MandeIonitrile and Prunasin, the Sources of Hydrogen Cyanide in All Stages of Paropsis atomaria (Coleoptera: Chysomelidae)

Abstract: Abstract (R)Mandelonitrile and the cyanogenic glucoside prunasin have been established as the source of HCN in all stages of the Australian beetle Paropsis atomaria. Quantitative data for both compounds and all life stages are presented. The larvae contain a β-glucosidase activity capable of hydrolysing prunasin and also β-cyanoalanine synthase activity enabling the disposal of free cyanide.

The rational mechanics and thermodynamics of polymeric fluids based upon the concept of a variable relaxed state

Abstract: The conceptual framework of polymer continuum mechanics based upon Eckart's idea of a variable relaxed state is developed. No constitutive models are explicitly used. The theory admits four constitutive functions only, the scalar specific internal energy, the vectorial heat flux, and two tensorial fluxes representing non-elastic stress and flow (slippage). The non-linearity of the constitutive relations includes self-induced anisotropy (Leonov) with Reiner-Rivlin's equation representing a special example for this. — The effectiveness of this non-linear theory is demonstrated by treating elongational flows of polymer melts.

Deterministic hydrological site and catchment models for the analysis of agroecosystems

Abstract: Summary This paper discusses two physical models which describe the water transport at sites and in catchments. The Deterministic Site Model consists of the submodels Evaporation, Transpiration, Interception, Heat Flux in the Soil, Soil Moisture Transport in the Matrix Pores and in the Macro Pores, Characterization of the Soil Physical Properties, Surface Crusting, Water Flux caused by Tile Drains and Lateral Water Flux. This model was tested using extensive data sets. The European Hydrological System/Systeme Hydrologique Europeen (SHE) is a distributed catchment model which was applied and tested. Based on first tests some components which had been tested successfully in applications of the Deterministic Site Model were substituted. Detailed validations showed the ability of the modified SHE to simulate water transports in agroecosystems.

Representation of rational Be´zier curves and surfaces by recursive algorithms

Abstract: Recursive algorithms for the computation and subdivision of rational Bezier curves and surfaces are presented. The development uses the relationship between the R 4 geometry and the rational scheme.