Showing papers by "Braunschweig University of Technology published in 1988"
1,312 citations
TL;DR: In this paper, the optimal reaction conditions for the production of d-alanine from d,l -5-methylhydantoin were investigated and found to be 55°C and pH 9.2.
114 citations
TL;DR: The authors found that the second sentence, cued by the first sentence, was more frequently recalled if the sentence pair was connected by "because" or if subjects were to think of causal relationships than if they were unconnected or connected by either "and" or "but".
92 citations
TL;DR: In this paper, the influence of convective heat transfer on the machine tool headstock has been investigated and two design and two compensatory methods investigated, which may be classified under the headings of design and compensation.
62 citations
TL;DR: It is suggested that the presynaptic muscarinic receptor that mediates inhibition of neurogenic contractions in rabbit vas deferens is of the ganglionic M1 beta-type.
55 citations
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49 citations
TL;DR: In this article, photophysical properties of three tetracene derivatives were investigated in solution and the quantum yield of intersystem crossing (Q ISC) and the fluorescence lifetime (τ F ) were determined according to an Arrhenius-type relationship.
44 citations
TL;DR: In this article, the authors combine observations of the magnetic field with the solar wind proton and alpha particle distributions to separate the three possible modes of propagation for hydromagnetic waves in the mass loaded solar wind upstream from the bow shock of a comet.
Abstract: The existence of hydromagnetic waves in the mass-loaded solar wind upstream from the bow shock of a comet is well-established both for comet Giacobini-Zinner and for comet Halley. Whereas previous reports have been concerned either with the magnetic field observations or with plasma observations, here we combine observations of the magnetic field with the solar wind proton and alpha particle distributions. This allows the three possible modes of propagation for these waves to be separated. The magnetic component is predominantly transverse to the magnetic field and linearly polarised. The flow vector also has a substantial amount of power parallel to the magnetic field. A examination of the pressure variations shows that slow magnetosonic waves are more common than the fast mode.
40 citations
TL;DR: Papaver somniferum L. (opium poppy) cells were elicited with a Botrytis sp.
Abstract: Papaver somniferum L. (opium poppy) cells were elicited with a Botrytis sp. homogenate and cultured by a semi-continuous process. Elicitation induced synthesis of sanguinarine and dihydrosanguinarine. Significant release of both alkaloids into the culture medium occurred. Medium exchange at 2-day intervals enabled product recovery from spent medium and maintained culture viability. Culture growth was not inhibited by elicitor treatment necessitating sub-culture prior to re-elicitation. Re-elicited cultures displayed an increasing sensitivity (reduced growth rate, higher alkaloid yield) to the elicitor with each successive treatment and did not survive a fourth elicitation.
35 citations
TL;DR: In this article, the authors consider the weights of quadrature formulas which are optimal in the sense of Sard for the evaluation of weighted integrals, and give an estimate of the size of the weights, and prove generalizations of the first and second conjecture of Meyers and Sard.
Abstract: We consider the weights of quadrature formulas which are optimal in the sense of Sard for the evaluation of weighted integrals. The nodes of the quadrature formulas have to obey certain restrictions, but all nodes common in quadrature theory are possible choices (e.g. the nodes of the Gauss-Legendre formulas). In this context, we give an estimate of the size of the weights, and we prove generalizations of the first and second conjecture of Meyers and Sard. As a consequence of the generalized first conjecture, Sard's quadrature formulas satisfy the Trapezoid and Circle Theorem, which were proven for Gauss-type quadrature formulas by Davis and Rabinowitz.
33 citations
TL;DR: In this article, a technique de calorimetrie a l'etude cinetique de restauration and recristallisation en determinant les forces conductrices of ces processus is applied.
TL;DR: In this article, the authors consider the impact of individual active abrasive grains on the machinability of workpiece materials and introduce a characteristic value to describe the machining ability of the cutting grain.
TL;DR: Thirty strains of microorganisms (bacteria, yeasts, fungi and green algae) were tested as resting free cells for their ability to transform acetyldimethylphenylsilane enantioselectively into (R)-(1-hydroxyethyl)dimethylphenolsilane [(R)−2].
Abstract: Thirty strains of microorganisms (bacteria, yeasts, fungi and green algae) were tested as resting free cells for their ability to transform acetyldimethylphenylsilane (1) enantioselectively into (R)-(1-hydroxyethyl)dimethylphenylsilane [(R)−2]. The biotransformations were monitored by GC (packed OV-17 column) and the enantiomeric purities of the products isolated were determined by HPLC (cellulose triacetate column, UV detection). All microorganisms tested were found to reduce 1 enantioselectively to give (R)-2. Under the test conditions used, the yeastTrigonopsis variabilis (DSM 70714) was found to exhibit the highest specific activity (1.5 mg product x g cell wet mass−1 x min−1), whereas the highest enantioselectivities were observed for the bacteriaAcinetobacter calcoaceticus (ATCC 31012) (>95% ee),Brevibacterium species (ATCC 21860) (90% ee) andCorynebacterium dioxydans (ATCC 21766) (>95% ee), the yeastCandida humicola (DSM 70067) (90% ee), the fungusCunninghamella elegans (ATCC 26269) (94% ee), as well as the cyanobacteriumSynechococcus leopoliensis (94% ee). From the green algae tested,Chlamydomonas reinhardii showed the highest enantioselectivity (85% ee).
TL;DR: In larvae and later developmental stages of Creatonotos transiens, which had been reared on the pyrrolizidine alkaloid 7S-heliotrine, a new major metabolite was detected by capillary GLC.
Abstract: Abstract In larvae and later developmental stages of Creatonotos transiens, which had been reared on the pyrrolizidine alkaloid 7S-heliotrine, a new major metabolite was detected by capillary GLC. The structure of this metabolite was determined by GLC-MS (EI, CI-MS) and 13C NMR to be 7Rheliotrine and 7R-heliotrine-N-oxide. 7R-Heliotrine is likely to be the direct precursor for the pheromone R( - )-hydroxydanaidal.
TL;DR: In this article, the instrumental parameters of a heat-flux DSC are now determined at two temperatures whereby the accuracy of the results is improved, and the method also allows a more exact determination of fusion temperature.
Journal Article•
TL;DR: In this paper, the continuite geometrique d'une courbe composite is defined as "continuity of geometriques d'ordre n and continuite des invariants geometriaques".
Abstract: Definition de la continuite geometrique d'une courbe composite. Etude des contacts d'ordre n et de la continuite des invariants geometriques
01 May 1988
TL;DR: Ausgehend von der Transversalflus-Anordnung des magnetischen Kreises wird fur permanentmagneterregte Synchronmaschinen die Berechnungsmethode beschrieben.
Abstract: Ausgehend von der Transversalflus-Anordnung des magnetischen Kreises wird fur permanentmagneterregte Synchronmaschinen die Berechnungsmethode beschrieben. Hierbei ist vorausgesetzt, das durch Wechselrichterspeisung die Stromform naherungsweise trapezformig vorgegeben ist. Fur ein- und zweiseitige Statoranordnungen sowie Erregersysteme in Flachmagnet- und Sammlerkonfiguration werden die mathematischen Beziehungen zwischen Feld- und Stromgrosen und den Abmessungsparametern angegeben. Es wird auf verschiedene Verfeinerungsstufen des Berechnungsverfahrens, etwa durch Berucksichtigung von Streufluskomponenten und Sattigung des Eisenwegs, hingewiesen. Vergleiche mit der dreidimensionalen FE-Methode und mit Messungen an einem Modellmotor beschliesen die Arbeit.
TL;DR: It is concluded that mouthbrooding is a low-cost strategy profiting from investments made during the preceding nonreproductive phase, and the implications for the evolution of mouth Brooding are discussed within the context of ecological constraints.
Abstract: Energy costs of mouthbrooding were investigated in the East African maternal mouthbrooder Pseudocrenilabrus multicolor by measuring rates of oxygen consumption. Mothers with their brood in the mouth expended 15.7% more energy than mothers without their brood and 13.8% more than starving nonreproductive controls. After subtracting the energy expenditure of the brood, the excess is reduced to 4.7% and 3.2%, respectively, a difference that is not statistically significant. By contrast, feeding nonreproductive females expended more than twice as much energy as the other groups. We conclude that mouthbrooding is a low-cost strategy profiting from investments made during the preceding nonreproductive phase. The implications for the evolution of mouthbrooding are discussed within the context of ecological constraints.
TL;DR: The potential of rubrene as a laser dye was investigated in deaerated solutions with a XeCl excimer laser as pump source in this article, where the (S1-S2) absorption band strongly overlaps with the fluorescence spectrum and thus ESA constitutes an important loss factor in the lasing process.
Abstract: The potential of rubrene as a laser dye was investigated in deaerated solutions with a XeCl excimer laser as pump source Laser tuning range, quantum efficiency and photostability as well as excited singlet state absorption (ESA) spectra were measured The (S1-S2) absorption band strongly overlaps with the fluorescence spectrum and thus ESA constitutes an important loss factor in the lasing process while triplet absorption can be neglected in the wavelength region of interest Laser performance of rubrene is superior compared to other polycyclic aromatic hydrocarbons which can be considered as model compounds of the lasing process in organic dyes
TL;DR: In this paper, the evolution of an ion induced collision cascade in a solid medium is studied by means of a DPl-approximation to the linear transport equation, and the effect of the anisotropy of the energy independent scattering cross section is given.
Abstract: The evolution of an ion induced collision cascade in a solid medium is studied by means of a DPl-approximation to the linear transport equation. Infinite medium and half space geometries are considered. Special attention is given to the effect of the anisotropy of the energy independent scattering cross section. We present results on the spatial distribution of particles moving at different energies, and the energy and angle distribution at the target surface. The spatial distributions are found to obey simple scaling laws; the energy and angular distributions are independent of the form of the scattering cross section, unless it is very strongly forward peaked.
TL;DR: In this article, a model for the life prediction for low cycle fatigue with hold time at tensile peak strain is suggested for the temperature range of 0.5T to 2T m. The model is checked by experimental results with various hold time periods.
Abstract: In low cycle fatigue at elevated temperature, the interaction between fatigue crack and creep damages is known to be responsible for the significant reduction of the fatigue life. In this investigation, a model for the life prediction for low cycle fatigue with hold time at tensile peak strain is suggested for the temperature range of 0.5T
m. This model is formulated on the basis of the assumptions that the creep cavities are formed due to the vacancies generated during fatigue, and are grown during the hold period. The fatigue crack nucleated at the surface due to fatigue loading is affected by the creep damages for its propagation. The model is checked by experimental results with various hold time periods. The predicted creep-fatigue lives are in good agreement with experimentally observed ones for 304 stainless steel and 13CrMo44 steel.
01 Jan 1988
TL;DR: In this article, the Peano kernel was used to estimate the quadrature error for polynomials of degree s − 1, where s is a nonnegative integrable weight function.
Abstract: Many interpolation quadrature rules
$$ {Q_n}\left[ f \right] = \sum\limits_{v = 1}^n {{a_v}f({x_v}) \approx I\left[ f \right]} = \int_{ - 1}^1 {f(x)} w(x)dx,\quad - 1{x_1} < {x_2} < \ldots < {x_n}1 $$
, where w is a nonnegative integrable weight function, are known to be appropriate for the integration of functions having sufficiently high derivatives. On the other hand, little is known on the quadrature error R n = I − Q n in the spaces A s [−1, 1], s ≪ n, consisting of all functions with an s − 1th absolutely continuous derivative. If Q n is exact for polynomials of degree s − 1, the error can be estimated for every f ∈ A s [−1, 1] by using the s th Peano kernel:
$$ \begin{array}{*{20}{c}} {{R_n}\left[ f \right] = \int_{ - 1}^1 {{f^s}(x)} {K_s}(x)dx,} \\ {{K_s}(x) = {R_n}\left[ {\frac{{(\cdot - x)_ + ^{s - 1}}}{{(s - 1)!}}} \right],\quad where\;t_ + ^{s - 1}: = \frac{1}{2}(1 + \operatorname{sgn} t)\cdot{t^{s - 1}}} \end{array} $$
(cf. Bras [1], p.39). We therefore have the unimprovable bounds
$$ \left| {{R_n}\left[ f \right]\left| {{{\left\| {{K_s}} \right\|}_p}\cdot{{\left\| {{f^{\left( s \right)}}} \right\|}_q};\;\frac{1}{p} + \frac{1}{q} = 1,1 < q\infty } \right.} \right. $$
and
$$ \left| {{R_n}\left[ f \right]\left| \leqslant \right.{{\left\| {{K_s}} \right\|}_\infty } \cdot Var\;{f^{\left( {s - 1} \right)}}.} \right. $$
(1.1)
TL;DR: Algorithms that use repeated linear interpolation of points, such as the de Boor algorithm but also the Aiken-Neville algorithm, will be considered and their common geometric structure will be discussed from a more general viewpoint.
01 Jan 1988
TL;DR: In this paper, the authors examine various problems of statistical inference under the presence of vagueness, and discuss the problem of confidence estimation where the available data are imprecise.
Abstract: In this paper we examine various problems of statistical inference under the presence of vagueness. More specifically, we discuss the problem of confidence estimation where the available data are imprecise. We indicate some possible applications.
15 Jun 1988
TL;DR: This paper presents an algorithm how to construct deterministic transition graphs from temporal formulae in a bottom-up way corresponding to the formula structure to ensure at least provisional admissibility of system behaviour up to a present state and at most potential admissability of future behaviour.
Abstract: Here systems, in particular database systems, are considered whose dynamic behaviour is characterized by state sequences that evolve stepwise, and whose integrity constraints are specified by means of temporal logic. Monitoring temporal formulae in state sequences can be reduced to following paths in transition graphs by only checking nontemporal edge labels in each state. This paper presents an algorithm how to construct deterministic transition graphs from temporal formulae in a bottom-up way corresponding to the formula structure. These graphs ensure at least provisional admissibility of system behaviour up to a present state and at most potential admissibility of future behaviour. Moreover, deterministic graphs have considerable advantages over general transition graphs.
01 Jan 1988
TL;DR: In this article, a power function for cavity growth is proposed to predict fatigue life under high-temperature low-cycle fatigue conditions with superimposed hold times, and the predicted values show excellent agreement, indicating the important role of creep cavitation for creep-fatigue life prediction.
Abstract: An attempt is made to predict fatigue life under high-temperature low-cycle fatigue conditions with superimposed hold times. It is well recognized that a reduction in life in this region is caused by the nucleation and growth of cavities along grain boundaries. The cavities can be formed by vacancy clustering, dislocation pileup, and grain boundary sliding. The subsequent growth leads to grain boundary cracking and intergranular fracture. The possibility of unstable crack advance is given if the crack tip opening displacement becomes equal to a critical cavity configuration. To describe this configuration we postulate a power function for cavity growth. Experimental data and the predicted values show excellent agreement, indicating the important role of creep cavitation for creep-fatigue life prediction.
TL;DR: In this paper, it is known that the addition of steel fibres leads to a reduction of crack width of bending elements in reinforced concrete, however, it is not established whether this effect is only due to the proven transfer of tensile force by the fibres across cracks or also because of an improvement of bond of the embedded deformed bar reinforcement by fibres.
TL;DR: In this article, a recherche de bacteries clivant stereospecifiquement les hydantoines is effectuee, and two arthrobacters possedent des enzymes stereosepecifiques.
Abstract: Les hydantoines monosubstitues sont les substrats d'hydantoinases qui les transforment en D ou L carbanoyl-acides amines, lesquels sont transformes en D ou L acides amines par une carbamoylase. Une recherche de bacteries clivant stereospecifiquement les hydantoines est effectuee. Deux arthrobacters possedent des enzymes stereospecifiques: ce sont les Arthrobacter crystallopoietes AM2 et Arthrobacter spec. DSM 3747
TL;DR: In this article, an analytical approach for finding the critical parameter sets for the Hopf bifurcation of the previous stationary state is presented, where numerical simulations have proved the occurrence of the strange attractor near the critical values of the parameters.
Abstract: The mechanical oscillator with dry friction. Duffing type nonlinearity and exciting periodic force is investigated. An analytical approach is presented for finding the critical parameter sets for the Hopf bifurcation of the previous stationary state. The numerical simulations has proved the occurrence of the strange attractor near the critical values of the parameters.
TL;DR: In this article, the trimethylsilylallenes 3a - f were obtained in excellent yields when the propargylic precursors 2a-f were subjected to low pressure flow pyrolysis at ca. 620°C.