Showing papers by "University of Paderborn published in 1980"

Experimental Results and Problems Concerning “Blue Phases”

Abstract: Most of the cholesteric mesophases formed by esters of cholesterol exhibit selective reflection of circularly polarized light in the u. v. region at temperatures close below the clearing point /1/. The well known reflection colours in the visible either occur near phase transitions to the smectic phase or in so-called compensated mixtures /1/. However, cooling down cholesteric esters only a few tenths of a Kelvin below the clearing point bright colours appear (mostly blue colours) which disappear on further cooling /2/. As early as in 1906 Lehmann /3/ noted that these colours belong to an optically isotropic modification. In his opinion this modification represents a stable phase distinct from that of the ordinary cholesteric one.

4-Amino-7-(β-D-arabinofuranosyl)pyrrolo[2,3-d]pyrimidin — die Synthese von Ara-Tubercidin durch Phasentransferkatalyse

Abstract: Aus 4-Chlor-2-methylthio-7H-pyrrolo[2,3-d]pyrimidin (6e) und 1-Brom-2,3,5-tri-O-benzyl-D-arabinofuranose (7) konnen durch Phasentransferkatalyse mit Benzyltriethylammoniumchlorid die Nucleosidderivate 8/9a in 85proz. Ausbeute erhalten werden. Diese werden chromatographisch getrennt und deren Anomerenverhaltnis (β: α) mit 8:2 bestimmt. Durch Ammonolyse von 9a entsteht 9d; Entschwefelung von 9d mit Raney-Nickel fuhrt zu 9e, dessen Benzylschutzgruppen durch katalytische Hydrierung abgespalten werden. Nach Ionentauscherchromatographie erhalt man kristallisiertes 4-Amino-7-(β-D-arabinofuranosyl)pyrrolo[2,3-d]pyrimidin (3), das im Gegensatz zum virostatisch aktiven Ara-A (1) durch Adenosin-Desaminase nicht desaminiert wird. 4-Amino-7-(β-D-arabinofuranosyl)pyrrolo[2,3-d]pyrimidine — the Synthesis of Ara Tubercidin by Phase Transfer Catalysis 4-Chloro-2-methylthio-7H-pyrrolo[2,3-d]pyrimidine (6e) and 1-bromo-2,3,5-tri-O-benzyl-D-arabinofuranose (7) react in the presence of benzyltriethylammonium chloride as phase transfer catalyst to give the nucleoside derivatives 8/9a in 85% yield. The latter were separated chromatographically, and the ratio of the anomers was determined to 8:2 (β: α). 9a was converted into 9d by ammonolysis and the desulfurisation, yielding 9e, was accomplished with raney nickel. The benzyl protecting groups in 9e, are split off by catalytic hydrogenation, and crystalline 4-amino-7-(β-D-arabinofuranosyl)pyrrolo[2,3-d]pyrimidine (3) was obtained after ion exchange chromatography. 7-Deaza-Ara A (3) is in contrast to Ara-A (1) not deaminated by adenosine deaminase.

Application of ENDOR-Induced Electron Spin Resonance to the Study of Point Defects in Solids

Abstract: The technique of ENDOR-induced ESR (EI-ESR) is applied to the investigation of several point defects in insulating crystals. It is shown that the lineshape of the EI-ESR spectrum depends on the ENDOR line used for the experiment. The EI-ESR technique allows the separation of overlapping ESR spectra in the presence of several defects. New applications are the selection of spin states and the determination of relative signs of spin-Hamiltonian parameters, the selection of centre orientations and the assignment of nuclei in complex ENDOR spectra, and the determination of quadrupole interactions which are not resolved in the ENDOR spectrum. Die Methode der ENDOR-induzierten ESR (EI-ESR) wird auf die Untersuchung verschiedener Punktdefekte in Isolatorkristallen angewandt. Es wird gezeigt, das die Linienform des EI-ESR-Spektrums von der zum Experiment verwendeten ENDOR-Linie abhangt. EI-ESR erlaubt die Trennung uberlagerter ESR-Spektren in Gegenwart mehrerer Defekte. Neue Anwendungen sind die Auswahl von Spin-Zustanden und die Bestimmung relativer Vorzeichen von Parametern des Spin-Hamiltonoperators, die Auswahl von Zentrenorientierungen und die Zuordnung van Kernen in komplizierten ENDOR-Spektren sowie die Bestimmung von im ENDOR-Spektrum nicht aufgelosten Quadrupol-Wechselwirkungen.

Explicit formula for filter function of maximally flat nonrecursive digital filters

Abstract: A general formula for the filter function of maximally flat f.i.r. digital filters using modified Krawtchouk polynomials is presented. This formula permits a direct calculation of the filter weights. It is especially advantageous for either high or low passband/stopband width ratios.

Corona-discharge Treatment of Polypropylene films-Effects of Process Parameters

Abstract: Corona treatment of films, mainly polypropylene (PP)-copolymers, was studied at commercial levels in a 2.7 kVA treater. The films were produced on a flat-film extruder with chill rolls. Degree of treatment was characterized by power of the generator divided by web speed and width of film (m Ws/cm2). The effectiveness of the treatment was measured in terms of the polar and dispersion components of surface-energy, the peel adhesion of pressure sensitive tape (similar to ASTM Adhesion Ratio) and the peel adhesion of polyurethane adhesives. The polar component of surface energy is a measure of the effectiveness of corona pretreatment. For a given degree of treatment, the polar surface energy component becomes greater as the film cooling rate increases (and the degree of crystallization falls). A comparison of homopolymers and copolymers does, however, reveal that even where these have the same density or the same degree of crystallization one cannot count on them having equally-sized polar components...

Synthese von 7‐Desazainosin durch Phasentransferglycosidierung

Abstract: Synthesis of 7-Deazainosine by Phase Transfer Glycosidation Phase transfer glycosidation of 4-methoxy-2-methylthio-7H-pyrrolo[2,3-d]pyrimidine (2) with 2,3,5-tri-O-benzyl-1-bromo-D-ribose (3) leads to selective N-7 ribosidation giving a mixture of the anomers 4/5. They are separated chromatographically and the anomeric configuration is assigned by 1H and 13C NMR spectroscopy. The protecting groups of 5 were removed by hydrolysis (methyl ether), desulfurisation (methylthio residue) and catalytic hydrogenation (benzyl ether) yielding 7-(s-D-ribofuranosyl)pyrrolo[2,3-d]pyrimidine-4(3H)-one (1), the 7-deaza derivative of inosine.

Ribosidierung von Pyrrolo[2,3‐d]pyrimidinen in Gegenwart starker Basen

Abstract: Ribosidation of Pyrrolo[2,3-d]pyrimidines in the Presence of Strong Bases Glycosidation of the pyrrolo[2,3-d]pyrimidine derivative 3c with the tribenzylated halogenose 6b in strong alkaline medium under the conditions of phase transfer catalysis yields the anomers 9a and 10a. The latter are intermediates in the synthesis of the nucleoside Q as well as for preparation of 7-methyl-7-deazanucleosides. By condensation of the 4-chloro derivative 3a with the tribenzoylated halogenose 4b and sodium hydride, substitution at the carbon of the acyloxonium ion takes place and a reaction product with orthoamide structure is formed.

ENDOR Investigation of Atomic Hydrogen at Anion Sites in KCl

Abstract: By means of ESR and ENDOR the g-values, the hyperfine (hf), and superhyperfine (shf) interactions of four shells of neighbours of atomic hydrogen and deuterium at anion sites in KCl are determined. The shf interactions are strongly temperature-dependent and show large isotope effects. Both observations are due to vibrations of hydrogen. From the temperature dependence of the ENDOR data the frequency of the hydrogen vibrations could be determined. Mit Hilfe von ESR und ENDOR werden die g-Faktoren, die Hyperfein (hf)- und Superhyperfein (shf)-Wechselwirkungen von vier Schalen von Nachbarkernen von atomarem Wasserstoff und Deuterium auf Aniongitterplatz in KCl bestimmt. Die shf-Wechselwirkungen sind stark temperaturabhangig und zeigen einen grosen Isotopeneffekt. Beide Beobachtungen ruhren von Wasserstoffschwingungen her. Aus der Temperaturabhangigkeit der ENDOR-Daten konnte die Wasserstoffschwingungsfrequenz bestimmt werden.

A Model of the Blue Phase of Cholesteryl Esters

Abstract: A model of the so-called Blue Phase of cholesterogenic liquid crystalline systems is proposed with the molecular axes inclined to the helix axis by a critical angle of 54.74°. This model results in a spherical refraction indicatrix compatible with the lack of birefringence as well as with the cholesteric-like optical properties.

Grandjean-Cano steps in a wedge-shaped sample of liquid-crystalline ``Blue Phase''

Abstract: Cholesteric liquid crystals formed by esters of cholesterol and some chiral nematogenic compounds exhibit an additional helically structured liquid-crystalline phase slightly below the clearing point [1]; it is termed ~ Blue Phase\" (BP) because of its striking light-reflecting properties. Recently, we reported that some optical properties, e.g., selective reflection of circularly polarized light and anomalous dispersion of optical rotatory power, are closely similar to that observed in classical cholesterics [2]. However, BPs are non-birefringent (An=0) whereas in cholesterics An <0 [2, 3]. To explain these seemingly contradicting properties, different models have been proposed: cubic structures [4, 5], and a uniaxial helical structure with a local director tilted against the helix axes [6]. No decision for one of the two types of models has been possible on the bases of experimental results until now. During our investigation of helical pitches in cholesterics by the Cano method [7] we observed the occurrence of GrandjeanCano steps in wedge-shaped BP samples. In Fig. 1 a mixture of 42 mole % cholesteryl benzoate (CB) in 4-n-heptyloxy azoxybenzene (HOAB) between a rubbed convex lense and a plane plate is shown at 135.74 ~ By means of a Leitz Labolux polarizing microscope narrow Cano lines can be seen as in classical cholesterics. Because of the in-plane anchoring of molecules on the wedge surfaces in cholesterics, an undisturbed helical structure is only preserved if the sample thickness d is an integer of the half pitch p (d= m.p/2). Cano lines represent disclinations within the wedge between areas where the-helical structure is expanded or compressed, respectively. The observation of Cano lines in BPs as shown in Fig. 1 sarcely seems to be compatible with a cubic arrangement of helical axis [5], as an expansion or compression of the helical structure can only take place perpendicular to the wedge surface leading to a distortion of the cubic symmetry. In a tilted helical structure [6], however, a discontinuous twist of the local director occurs at the boundary between expanded and compressed areas, explaining the observed Cano disclinations.

Bounding the Bandwidth of NP-Complete Problems

Abstract: We study in this paper how the computational behaviour of NIP-complete graph problems is influenced by imposing a bound on the bandwidth. We show: (i) A large number of problems are considerably simpler for graphs of small bandwidth. On the other hand, there are problems which remain NIP-complete even for graphs of bandwidth 3. (ii) A large number of problems are equivalent under reductions which preserve bandwidth. All these problems are complete under bandwidth preserving reductions for a class RPP, which is defined by nondeterministic Turing machines operating with some space bound and simultaneous polynomial time. This indicates, because of earlier results, that "bandwidth" plays the same role for graph problems as "maximal number" does for number problems.

A comment on the generalized Liouville equation

Abstract: The generalized Liouville equation is studied in a new light using the Lie derivative of a differential form with respect to a vector field

On a Subclass of Pseudopolynomial Problems

Abstract: A subclass of the class of all pseudopolynomial problems is defined as a family of sets acceptable by some automaton operating with simultaneous time and space bounds That the class is large enough can be seen in that it contains many (if not all) of the pseudopolynomial problems described in the literature We study structure preserving reductions within this class and give intuitive reasons (borrowed from our knowledge about space bounded automata) that there exist at least four well known problems which are pairwise not equivalent under these reductions

A Two-Dimensional Thermodynamic Field Theory

Abstract: We represent a two-dimensional thermodynamic field theory and we apply this theory on an example, namely a mixture of heat conducting, inviscid fluids in a very thin layer with arbitrary shape. Such a fluid layer can be roughly spoken, considered as a fluid lipid bilayer (the thickness has an order of 10 nm) as well as a monolayer. We consider a semipermeable lipid bilayer with protein films as a model for a biological membrane which consists mainly of an ordered structure (like the smectic phase of liquid crystals). In the following considerations we shall give a description of continuous media and in a first step we shall not consider a polar media with ordered structure.

The pair distributions and the osmotic coefficient in anomalous electrolytes up to concentrations c≈ 1 mol/1

Abstract: The osmotic coefficient of anomalous electrolytes up to concentrations c ≈ 1 mol/l is explained by the pair distributions n(r) = exp[-β(Vc(r) + V(hs)(r) + V1(r))]. Here Vc(r) is a screened Coulomb potential, V(hs)(r) a hard sphere potential and V1(r) = −A/r6 a short range attractive potential. For the contact distances R++, R−− and R+− of the hard sphere potentials between ions with the same sign of their charges (++,−−) and ions of opposite charges (+−) the relations R++ = R−− = R and R+− = q1R with 0 < q1 < 1 are assumed. In contrast to a previous paper the parameter q1 takes a fixed value q1 ≈ 0,8. The constant A is determined by the fraction q2 defined by A/R6 = q2(Z2e2/DR) where the positive integer Z is the charge number of the ions and D the dielectric constant of the solvent. The numerical calculation of the osmotic coefficient of 1-1-valent hydrous electrolytes in the range of temperature 273 K ⩽ T ⪅ 293 K shows that the anomalous electrolytes are described by fractions q2 in the range 0,25 ⪅ q2 ⪅ 0,5 if the contact distances R are in the range 3 A ⩽ R ⩽ 7 A.

Discadenin‐Derivate ohne cytokininaktiven Δ2‐Isopentenylrest

Abstract: Discadenine Derivatives without Cytokinine Active Δ2-Isopentenyl Residue Alkylation of adenine with ethyl 4-bromo-2-L-phthalimidobutyrate yields the N-3-alkylated derivative 4a. After removal of the protecting groups in 4aL-(+)-discadenine without cytokinine active N6−Δ2-isopentenyl residue (3a) is obtained. It shows similar inhibition of the spore germination as L-(+)-discadenine (1). The derivatives 3b and c with modifications in the N-3 side chain are prepared analogously. The pKa value of 5.67 implies that protonation around the physiological pH value plays a key role in the biosynthesis and the regulatory function of discadenine.

Computer aided frequency response design with given poles

Abstract: Many design problems in the field of linear multivariable control systems can be reduced to the following: Given a set of transfer functions whose numerator polynomial coefficients depend linearly on some parameters. Determine the parameters such that the transfer function frequency responses fit to desired frequency responses as good as possible. A simple and straightforward solution of this problem is given with provision to concentrate the fitting on the desired frequency ranges. Some applications are outlined such as reference variable feedforward to dynamic compensators, disturbance response design, model reduction and single-input pole assignment compensator design.

Determination of Phenylurea Herbicides and their Metabolites by High Performance Liquid Chromatography

Abstract: A method for the determination of a herbicide and its metabolites is described. Furthermore it is shown that reversed-phase high-performance liquid chromatography is a powerful method for the separation und determination of several herbicides in a single run.

Small angle X-ray diffraction study of the liquid crystalline homologous series 4,4′-di-n-alkyl-azoxy-benzenes

Abstract: Although the l iqu id c rys ta l l ine concept of b~ological membranes is widely accepted, the relat ionship between molecular structure of the i r constituents (e.g. alkyl chain length of l i p ids , type of the i r polar groups) and the mesomorphic properties remains to a great extend unresolved, We investigated the phase transi t ions and order parameters of a thermotropic l iqu id crys ta l l ine system. This system, the homologous series of 4 ,4 ' -d i -n alkyl-azoxy-benzenes

Influence of Phase Transitions of Amphiphilic Monolayers on the Orientation of Liquid Crystals

Abstract: Monolayers of different pure lecithins were transferred from aqueous subphases to hydrophilic glass plates at different packing densities of the film. Samples of nematic and induced cholesteric liquid crystals were prepared with these plates. Polarizing microscopy showed that the director field prefers different orientations depending on packing density of the monolayer as well as on temperature of the sample. In particular lowering the temperature of a system substrate/liquid crystal results in the loss of the homeotropic orientation for the benefit of a tilted one. The same alteration of the director field orientation occurs at constant temperature with increasing packing density.