Showing papers by "University of Paderborn published in 1983"
TL;DR: In this article, a phase-transfer glycosylation of the chromophore 3a with the toluoyl-protected halogenose 6 was used to synthesize 2′-deoxytubercidin.
39 citations
TL;DR: The main contribution of this paper is an algorithm computing the shortest cycle of even length of an unweighted undirected graph within essentially 0 (|V|2) time.
Abstract: We study the problem of determining a shortest cycle of even length (or of odd length, respectively). For cycles of odd length we get the same complexity as for determining a shortest cycle of a graph i. e. 0 (|V|·|E|) in the case of unweighted graphs and 0 (|V|3) in the case of weighted graphs. The main contribution of this paper is an algorithm computing the shortest cycle of even length of an unweighted undirected graph within essentially 0 (|V|2) time.
33 citations
TL;DR: In this article, a system of coupled KdV equations which was conjectured to be integrable by Hirota and Satsuma is considered and an infinite hierarchy of commuting symmetries and conservation laws in involution is found.
31 citations
TL;DR: Acyclo-7-desazaguanosin (2,3-d]pyrimidin this paper was synthesized by a specific phase-transfer alkylation of 2-Amino-4-methoxy-7H-pyrrolo[2, 3-d]-pyrimidine.
31 citations
TL;DR: In this article, the chaotic behaviour and limit cycle behavior of the dynamical system x + α x + d V(x) d x = ƒ cos (Ωt) was investigated for various potentials V and parameters values α, ǫ and Ω.
31 citations
09 Mar 1983
TL;DR: This paper describes an approximation algorihm for the vertex cover problem which has a worst case ratio strictly smaller than 2 for graphs which don't have too many nodes and presents algorithms which improve in the case of degree bounded graphs the worst case ratios known up to now.
Abstract: In this paper we describe an approximation algorihm for the vertex cover problem which has a worst case ratio Δ strictly smaller than 2 for graphs which don't have too many nodes (for example Δ≤1.9 if |V|≤1o13). Furthermore we present algorithms which improve in the case of degree bounded graphs the worst case ratios known up to now.
20 citations
TL;DR: In this paper, a singular point analysis is performed to find integrable and non-integrable regions of the Rikitake two-disc dynamo system, which gives a hint where global constants of motion exist.
Abstract: To find integrable and nonintegrable regions of the Rikitake two disc dynamo system we investigate its Painleve property. This means we perform a singular point analysis. This analysis gives us a hint where global constants of motion exist. We also investigate related systems.
18 citations
TL;DR: 7-Deazahypoxanthine was found to be oxidised by cow's milk xanthine oxidase exclusively at carbon 2, and the resulting 7-deazaxanthine is a strong inhibitor of the enzymatic reaction, offering a possibility for determining the structural requirements of ligand binding separately for the first step.
Abstract: 7-Deazahypoxanthine was found to be oxidised by cow's milk xanthine oxidase exclusively at carbon 2. The resulting 7-deazaxanthine is a strong inhibitor of the enzymatic reaction. This offers a possibility for determining the structural requirements of ligand binding separately for the first step. All the monomethyl isomers of 7-deazahypoxanthine were tested as probes by measuring their Km, Ki and V values. While the N-3-methyl and C-7-methyl isomers are still processed, the N-9-methyl and 6-O-methyl isomers are bound as inhibitors to the active site. The N-1-methyl compound is neither an inhibitor nor a substrate. This demonstrates that HN(1) and O = C(6) are essential for the binding. Replacement of O = C(6) by S = C(6) changes the substrate into a strong inhibitor (Ki = 9 microM), implying that the electron transfer to the enzyme is hindered. Methylation of the thioxo group (S =) reduces the inhibition significantly. In contrast to 7-deazahypoxanthine, 2-thioxo-7-deazaxanthine is an activator at concentrations below 87 microM and a partial competitive inhibitor above this concentration, which implies the presence of a second binding site.
17 citations
01 Jan 1983
14 citations
TL;DR: In this paper, the filter functions of certain least-weighted-squares digital filters are derived explicitly by the use of discrete orthogonal functions (e.g. Hahn polynomials).
Abstract: Numerical convolution operations, executed on noise contaminated signals, are approximated by FIR digital filters in such a way that the effect of random coloured noise is minimized. Using elementary Hilbert space techniques, the filter functions of certain least-weighted-squares digital filters are derived explicitly by the use of discrete orthogonal functions (e.g. Hahn polynomials). the approach is suitable especially for narrowband operations such as smoothing, narrowband differentiation, and narrowband deconvolution (resolution enhancement). Examples of linear-phase lowpasses with monotone passband, obtained with the aid of Hahn polynomials, are discussed in detail. Also the well-known maximally flat digital lowpasses which can be derived with the aid of Krawtchouk polynomials, and narrowband differentiators are considered. In the case of least-weighted-squares approximation by Hahn polynomials, powerful recursive realizations can be developed to reduce computational requirements.
11 citations
TL;DR: In this paper, the magnetic susceptibility of Ti$(T,P) was determined at a field strength of 2.1 T as a function of both temperature from 3 to 300 K and hydrostatic pressure up to 1.3 GPa (13 kbar).
Abstract: The magnetic susceptibility $\ensuremath{\chi}(T,P)$ of Ti${\mathrm{Be}}_{2}$ is determined at a field strength of 2.1 T as a function of both temperature from 3 to 300 K and hydrostatic pressure up to 1.3 GPa (13 kbar). At low temperatures, $\ensuremath{\chi}$ is found to decrease under pressure, the degree of depression diminishing rapidly with increasing temperature from $\frac{\ensuremath{\partial}\mathrm{ln}\ensuremath{\chi}}{\ensuremath{\partial}P}=(\ensuremath{-}9.6\ifmmode\pm\else\textpm\fi{}0.4)%/\mathrm{GPa}\mathrm{at} 3 \mathrm{K}\mathrm{to} (0\ifmmode\pm\else\textpm\fi{}0.3)%/\mathrm{GPa}\mathrm{at} 300 \mathrm{K}$. Pressure is also found to suppress strongly the low-temperature anomaly in the field dependence of $\ensuremath{\chi}(H)$ at 5.6 T. An increase in the spin-fluctuation temperature with pressure is indicated, $\frac{\ensuremath{\partial}{T}_{\mathrm{SF}}}{\ensuremath{\partial}P}\ensuremath{\simeq}+3.5$ K/GPa, where ${T}_{\mathrm{SF}}(0)\ensuremath{\simeq}24$ K, although it is not possible to account for the present results in terms of the variation of a single characteristic energy. The Stoner factor appears to decrease rapidly under pressure. The pressure dependence of the lattice parameter for Ti${\mathrm{Be}}_{2}$ at room temperature is determined up to 27 GPa, yielding the initial compressibility $K=(7.6\ifmmode\pm\else\textpm\fi{}0.4)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ G${\mathrm{Pa}}^{\ensuremath{-}1}$. It is shown that the ferromagnetism of $\mathrm{Ti}{\mathrm{Be}}_{2\ensuremath{-}x}{\mathrm{Cu}}_{x}$ for $x\ensuremath{\ge}0.15$ cannot be due solely to the volume expansion associated with increasing $x$. Preliminary measurements indicate that substituting Mn for Ti in Ti${\mathrm{Be}}_{2}$ causes a strong decrease in the total magnetization in analogy with previous studies involving Fe substitution. A simple qualitative model of the electronic structure of Ti${\mathrm{Be}}_{2}$ near ${E}_{F}$ is suggested. Ti${\mathrm{Be}}_{2}$ is not superconducting at temperatures above 150 \ensuremath{\mu}K.
TL;DR: In this paper, the influence of long-range static energy fluctuations of the mobility edge on time-of-flight experiments is discussed, and it is shown that most of the observed experimental features follow from this model if the parameters used are those already inferred from the interpretation of dc transport data.
Abstract: The influence of longranged static energy fluctuations of the mobility edge on time-of-flight experiments is discussed. By extensive Monte Carlo calculations it is shown that most of the observed experimental features follow from this model if the parameters used are those already inferred from the interpretation of dc transport data.
TL;DR: In this paper, a kopplungssystem fur die Thermogravimetrie-Differentialthermoanalyse with der Massenspektrometrie wird beschrieben.
Abstract: Ein Kopplungssystem fur die Thermogravimetrie-Differentialthermoanalyse mit der Massenspektrometrie wird beschrieben. Die Arbeitsweise und die Vorzuge dieses Systems werden am thermischen Abbau und der simultanen massenspektrometrischen Untersuchung von Berylliumchelaten dargestellt.
TL;DR: In this article, the induction of blue phases (BPs) was observed in binary mixtures comprising nematogenic compounds and cholesteryl esters which do not exhibit BPs by themselves.
TL;DR: For doped n-type a-Si:H films rather generally a kink in the temperature dependence of the conductivity is observed near 400K which leads to an increase of the activation energy at higher temperatures as discussed by the authors.
Abstract: For doped n-type a-Si:H films rather generally a kink in the temperature dependence of the conductivity is observed near 400K which leads to an increase of the conductivity activation energy at higher temperatures. Models for the explanation are discussed with particular emphasis on our earlier suggestion of a doping-dependent density of states peak near midgap.
TL;DR: In this article, the Painleve property of anharmonic system with an external periodic field is investigated and it is shown that the only movable singularities exhibited by the solutions are poles.
TL;DR: In this paper, a trisilyl verbindung of Tubercidin with tert-Butyl(chloro)dimethylsilane gives the 2′,3,5′-tri-O-silyl derivative 1b.
TL;DR: In this article, the quasistatic thermal crack propagation in self-stressed unidirectionally reinforced composite structures with a low-fiber volume fraction has been investigated and the resulting mixed boundary value problems of the stationary plane thermoelasticity are solved numerically by using standard finite element programs.
01 Jan 1983
TL;DR: In this paper, the authors investigated the influence of an instationary temperature distribution on the behavior of a quasistatic extending interface crack in unidirectional carbon-aluminum composite structures.
Abstract: The quasistatic growth of thermal interface cracks in self-stressed unidirectionally reinforced composite structures has been studied on a micromechanical level of investigation. Therefore a circular unit cell of a unidirectional Carbon-Aluminum composite has been considered in order to investigate the influence of an instationary temperature distribution on the behaviour of a quasistatic extending interface crack. The resulting mixed boundary-value problem of the plane thermoelasticity has been solved numerically by using a standard finite element program with triangular linear strain six-node elements. Further, numerical results are given for the crack surface displacement u, the nodal point force F as well as the strain energy release rates G j (j=I, II) of a unidirectional Carbon-Aluminum composite.
TL;DR: In this paper, the authors summarized progress made in analyzing defect structures using electron nuclear double resonance (ENDOR) and showed the application and advantages of methods like endor-induced ESR and double endor measurement techniques.
Abstract: The paper summarizes progress made in analysing defect structures. For this electron spin resonance has long been a standard tool. However, its applicability is often very limited due to its insufficient power to resolve hyperfine structures, necessary to determine defect structures. Nuclear magnetic resonance provides high resolution, but insufficient sensitivity. The combination of both, electron nuclear double resonance (ENDOR), turned out to be the most powerful technique. However, complicated systems with low symmetry or with several types of defects present simultaneously usually yield very complex ENDOR spectra which cannot be analysed using “conventional” methods. Considerable progress was made by improving the experimental methods including computer assistance, processing of the data and novel ENDOR measurement techniques. The application and advantages of methods like ENDOR-induced ESR and DOUBLE ENDOR are demonstrated using several recent examples.
01 Jan 1983
TL;DR: Kontinuierliche Konturen sind fur die Erkennung von Bildmustern von groser Bedeutung Es wird ein Verfahren vorgestellt, das alle Elemente kontinierlicher Konturan erfast and codiert In einem hierarchischen Verknupfungsprozes werden benachbarte codierte Konturelemente in uberlappenden Teilbildfeldern explizit auf Kontinuitat uberpru
Abstract: Kontinuierliche Konturen sind fur die Erkennung von Bildmustern von groser Bedeutung Es wird ein Verfahren vorgestellt, das alle Elemente kontinuierlicher Konturen erfast und codiert In einem hierarchischen Verknupfungsprozes werden benachbarte codierte Konturelemente in uberlappenden Teilbildfeldern explizit auf Kontinuitat uberpruft Da die Grose der Teilbildfelder und damit die kombinatorische Vielfalt der Verknupfungsmoglichkeiten von Ebene zu Ebene der Verknupfungshierarchie wachst, werden auf jeder Ebene Sequenzen von Konturelementen mit ahnlichem Verlauf bei der Codierung nicht mehr unterschieden Dies fuhrt zu einer hierarchischen Verallgemeinerung der Form zugunsten einer weitraumigen systematischen Uberprufung der Kontinuitat Der dabei erzeugte hierarchische Konturcode ermoglicht einem Mustererkennungssystem optimalen Zugriff auf Information uber Verlauf und Kontinuitat von Konturen
TL;DR: In this article, the Fokker-Planck equation of a macroscopic system is expanded with respect to the velocity in terms of orthogonal functions, e.g. Hermite functions, and a hierarchy of equations for the expansion coefficients is obtained.
Abstract: If the kinetic equation of a macroscopic system is expanded with respect to the velocity in terms of orthogonal functions, e.g., in terms of Hermite functions, one obtains an infinite hierarchy of equations for the expansion coefficients. Grad's method consists in truncating this hierarchy and investigating the remaining finite system. In this paper we set up conditions under which this procedure is rigorously justified in case of the Fokker-Planck equation.
TL;DR: In this article, rational solutions to linear and nonlinear equations were derived by using similarity methods for linear equations and auto-Backlund transformations for non-linear equations, and it was shown that rational solutions can be generated using similarity method for linear and Backlund transformation for nonlinear problems.
Abstract: We study rational solutions to certain linear and nonlinear equations. It is shown that rational solutions can be generated by using similarity methods for linear equations and auto-Backlund transformations for nonlinear equations.
TL;DR: In this paper, a phase-transfer glycosylation of 4-methylthio-7H-pyrrolo[2,3-d]pyrimidin with 1-bromo 2,3,5-tri-O-benzyl-D-arabinofuranose is described.
TL;DR: Several bis(4-Cl-acetoacetanilide)Cu(II) adducts with 1.10-phenanthroline and 2,2′-bipyridine were prepared and identified by elemental analysis and spectroscopic methods.
TL;DR: In this article, the MCD of the UV absorption bands with dominating Faraday C terms is measured via the MCC of the FeCl 2 quenched at LHT and yields a negative Curie-Weiss θ thus indicating speromagnetic spin order.
TL;DR: In this article, the temperature and field dependent magnetization of quasi-2D ferromagnets K 2 CuF 4 and Rb 2 CrCl 4 was measured near T c within the easy c planes using linear magnetic birefringence.
TL;DR: In this paper, phase-transfer glycosylation of 2-amino-4-methoxy-7 H -pyrrolo[2,3-d ]pyrimidine with 2,3,5-tri-O -benzyl-d -arabinofuranosyl bromide in benzene was performed.
TL;DR: In this article, the electric conductivity of stationary and homogeneous electrolytes at high electric fields is investigated and it is shown that the increase of the molar conductivity can be explained only by an additional boundary condition in the differential equation for the pair distribution.
Abstract: Following a previous paper the electric conductivity of stationary and homogeneous electrolytes at high electric fields is investigated. It turns out that the increase of the molar conductivity at high electric fields which is observed experimentally can be explained only if an additional boundary condition in the differential equation for the pair distribution is taken into account. As a consequence also the electric conductivity at low electric fields is modified. The numerical results for hydrous electrolytes are in a good agreement with experimental data.