Showing papers by "University of Paderborn published in 1981"

On the Orientation of Liquid Crystals by Monolayers of Amphiphilic Molecules

Abstract: Uniform director field of liquid crystal cells may be induced by surface action which is known as phenomena in many varieties. The hometropic orientation of a liquid crystal may be enforced by a just coherent monolayer of suitable amphiphilic compounds on solid substrates. Polarizing microscopy of nematics and helix unwinding of cholesterics /1/ showed the orientation of the director field in this case to be influenced by the following parameters: 1. temperature; 2. physical properties of the substrate surface (micro geometry, packing density of the amphiphilic monolayer,…); 3. chemical properties of the substrate (structure of the amphiphilic compounds,…); 4. structure of the liquid crystal molecules.

Synthese von 2‐Amino‐3, 7‐(β‐D‐ribofuranosyl)‐4H‐pyrrolo[2,3‐d] pyrimidin‐4‐on ‐ 7‐Desazaguanosin ‐ der Stammverbindung des Nucleosids Q

Abstract: 2-Amino-3 7,dihydro-7(β-D-ribofuranosyl)4H-pyrrolo[2,3-d]pyrimidin-4-on (1a), die Stammverbindung des seltenen Nucleosids Q, wurde aus dem durch Phasentransferglycosylierung erhaltenen Pyrrolo [2,3-d]pyrimidin-Derivat 3a11) dargestellt. N-3-Alkylierung von 3a durch Chlormethyl-isopropyl-ether fuhrt zu 3b und Austausch der 2-Methylthiogruppe in einer NaH/Acetamid-Schmelze zum geschutzten 7-Desazaguanosin 3c. Bortrichlorid im Methylenchlorid entfernt bei - 78°C sowohl den Isopropoxymethylrest als auch die Benzylschutzgruppen unter Bildung von 4c. Nach dessen Ammonolyse erhalt man 7-Desazaguanosin (1a), das im Gegensatz zu Guanosin einen anomal schwachen Cotton-Effekt zeigt, der auf starke konformative Beweglichkeit der Nucleobase an der N-glycosylischen Bindung hinweist. Synthesis of 2-Amino-3, 7-dihydro-7(β-D-ribofuranosyl)-4H-pyrrolo[2,3-d]pyrimidin-one - 7-Deazaguanosine - the Parent Compound of the Nucleoside Q 2-Amino-3, 7-dihydro-7-(β-D-ribofuranosyl)-4H-pyrrolo[2,3-d]pyrimidin-4-one (1a), the parent compound o e rare nucleoside Q, has been synthesized using the pyrrolo [2,3d]pyrimidine derivative 3a11) which was available by phase transfer glycosylation. N-3 alkylation of 3a with chloromethyl isopropyl ether yields 3b, which reacted in a molten mixture of sodium hydride/acetamide to give 3c. Boron trichloride in methylene chloride removes the isopropoxymethyl as well as the benzyl groups at - 78°C simultaneously with formation of 4c. After ammonolysis of 4c 7-deazaguanosine &1par;la) was obtained. IN contrast to guanosine, la shows an anomalous weak Cotton effect implying an unusual flexibility of the nucleobase around the N-glycosylic bond.

Balance equations for micromorphic materials

Abstract: The balance laws for micromorphic continua of degree 1 are derived by means of classical statistical mechanics. The equations derived by Eringenet al. [Continuum Physics, Vol. IV (Academic, New York, 1976)] are obtained in a slightly generalized form. Explicit expressions for the stress, the couple stress, the spin production, and the heat flux are given in terms of microscopical variables.

Determination of elasticity and viscosity coefficients in a ferroelectric smectic c liquid crystal

Abstract: Experimental methods of determination of the twist elasticity and rotational viscosity coefficient in ferroelectric smectics C are described. Temperature dependences of the coefficients obtained for a typical smectic C liquid crystal are presented.

The Hall mobility in amorphous semiconductors in the presence of long-range potential fluctuations

Abstract: We have recently proposed that, for an amorphous semiconductor, the ‘activated’ behaviour of Q(T) = ln [sgrave](T) + e/kS(T), where [sgrave] is the conductivity and S the thermopower, can be understood on the basis of diffusive transport above a mobility edge, if this mobility edge is affected by the static random potential caused by charged centres. This activated behaviour for Q(T) is found in many amorphous systems including, and best documented for, glow-discharge (gd) deposited Si : H. The model is extended to a calculation of the Hall mobility in the presence of the random field. The treatment is based on the random phase model, i.e. the Hall mobility is independent of temperature for an undisturbed mobility edge. Comparison with experimental data for doped gd Si : H is made and satisfactory agreement is obtained.

Die isomeren 4-Amino-N-methylpyrrolo[2,3-d]pyrimidine

Abstract: Die Methylierung von 4-Amino-7H-pyrrolo[2,3,-d]pyrimidin (2a) fuhrt im Neutralen zu einer 1: 1-Mischung der N-1-(6a) und N-3-Isomeren 5a). Die Konstitutionszuordnung erfolgte durch Dimroth-Umlagerung von 5a zu 2e. Das Isomer 6a kann auch durch Entschwefelung des Thioderivates 4a erhalten werden; letzteres uberwiegt (3:1) bei der Cyclisierung des Pyrimidin-Derivates 3. Die selektive N-7-Methylierung von 2a bzw. 2b erfolgte durch Phasentransfermethylierung im alkalischen Medium. The Isomeric 4-Amino-N-methylpyrrolo[2,3-d]pyrimidines Methylation of 4-amino-7H-pyrrolo[2,3-d]pyrimidine (2a) (neutral conditions) leads to a 1:1 mixture of N-1 (6a) and N-3 isomers (5a). The structural assignment was accomplished by Dimroth rearrangement of 5a yielding 2e. The isomer 6a is also obtained by desulfurisation of the thio derivative 4a; the latter predominates (3:1) in cyclisation of the pyrimidine derivative 3. Selective N-7 methylation of 2a or 2b was achieved by phase transfer methylation under alkaline conditions.

Synthese von Ara‐Tubercidin und seiner 5′‐Phosphate über Phasentransfer‐Glycosylierung von 4‐Amino‐2‐methylthio‐7H‐pyrrolo[2,3‐d]pyrimidin

Abstract: Phasentransfer-Glycosylierung von 4-Amino-2-methylthio-7H-pyrrolo[2,3-d]pyrimidin (3a) mit 2,3,5-Tri-O-benzyl-1-brom-D-arabinofuranose fuhrt in 83% Ausbeute zu den anomeren Nucleosid-Derivaten 4a/5a, die chromatographisch getrennt werden und deren Anomerenverhaltnis (β:α) mit 4.9:1 gefunden wird. Raney-Nickel entfernt die Methylthioreste und nach hydrierender Abspaltung der Benzylschutzgruppen erhalt man 4-Amino-7-(β-D-arabinofuranosyl)pyrrolo[2,3-d]pyrimidin (1a) und sein α-Anomeres (6). Aus dem β-Anomeren 1a (Ara-Tubercidin) wird mit POCL3 das 5′-Monophosphat 1b erhalten, das im Gegensatz zu Ara Ara-AMP (2b) von AMP-Desaminase nicht desaminiert wird. 1b wird durch Kondensation mit Mono[trioctylammonium]orthophosphat bzw. Di[tributylammonium]pyrophosphat und 1,1′-Carbonyldiimidazol in das 5′-Diphosphat 1c und das 5′-Triphosphat 1d ubergefuhrt. Synthesis of Ara Tubercidin and its 5′-Phosphates via Phase Transfer Glycosylation of 4-Amino-2-methylthio-7H-pyrrolo[2,3-d]pyrimidine Phase transfer glycosylation of 4-amino-2-methylthio-7H-pyrrolo[2,3-d]pyrimidine (3a) with 2,3,5-tri-O-benzyl-1-bromo-D-arabinofuranose gives the anomeric nucleoside derivatives 4a/5a in 83% yield. They are separated chromatographically and the ratio of anomers (β:α) is found to be 4.9:1. The methylthio residues are removed with Raney nickel catalyst and the benzyl protecting groups are split off by hydrogenation leading to 4-amino-7-(β-D-arabinofuranosyl)pyrrolo[2,3-d]pyrimidine (1a) and to its α-anomer (6). The 5′-monophosphate 1b, obtained from 1a by treatment with POCL3, cannot be deaminated with AMP deaminase which is in contrast to ara AMP (2b).1b is converted to the 5′-diphosphate 1c or the 5′-triphosphate 1d by condensation with either mono[trioctylammonium] orthophosphate or di[tributylammonium] pyrophosphate and 1,1′-carbonyldiimidazole.

Linearization Procedure and Nonlinear Systems of Differential and Difference Equations

Abstract: Carleman [1] showed that an autonomous finite dimensional nonlinear system of differential equations x=f(x) can be embedded into an infinite linear system of differential equations, where the f. are polynomial in x. Recently, several authors [2–7] have taken up this idea and solved nonlinear differential equations within this approach. Steeb and Wilhelm [4] have written the original system with the help of the Kronecker product ⊗ as: x=Ax+B(x⊗x)+..+Z(x⊗x⊗…⊗x), where A,B,..,Z are matrices with constant coefficients. They calculated the time evolution of x⊗x, x⊗x⊗x and so on and obtained an infinite system with simple block structure, whereas the infinite system obtained from Carleman linearization has no simple block structure and must be rearranged before this can be obtained. The infinite system can easily be expressed with the help of Bose operators. The infinite system and the finite system are not equivalent, because the infinite system admits solutions which are not solutions of the finite system. However, if we restrict ourselves to analytical solutions, then the two approaches are equivalent. When we solve the infinite system by Laplace transformation or an exponential ansatz, we are forced to consider carefully the problem of convergence. When we cut off the infinite system at some finite dimension, we do not, in general, find a good approximation, in particular for large times. However, when the original system admits only asymtotically stable stationary solutions, such an approximation can be carried out. Recently, Steeb [7] applied the approach to nonlinear difference equations. The solution of the logistic equation x(t+1)=ax(t)(1−x(t)) (t=1,2,..) for a=4 can be determined. The ansatz xn(t):=(x(t))n leads to the linear infinite system $${x_n}(t + 1) = {a^n}\sum\limits_{r = 0}^n {{{( - 1)}^r}} \left( {\begin{array}{*{20}{c}} n \\ r \end{array}} \right){x_{n + r}}(t)$$ .

Gas-chromatographische Trennung freier polarer Verbindungen mit Glascapillar-Säulen

Abstract: Es wird gezeigt, auf welche Weise Glascapillarsaulen fur die Trennung freier polarer Verbindungen mit breitem Polaritatsbereich zu optimieren sind. Das Trennverhalten wird einmal durch eine irreversible Zerstorung des Phasenunterbaues und zum anderen durch reversible Veranderungen an der Phasenoberflache negativ beeinflust. Es wird ein Regenerationsverfahren mit alkoholischer Oxalsaurelosung beschrieben, das diese Einflusse teilweise ruckgangig macht.

A characterization of totally normal structure

Abstract: In this note it is proved that a subsetA of a locally convex topological vector spaceE has normal structure with respect to every continuous seminorm onE — called totally normal structure — iff every bounded convex subset ofA is precompact. Some consequences are discussed.

A Note on the nonrelativistic and relativistic classical mechanics and the constants of the motion

Abstract: Let V = ~(x, v, t) 818x + ~(x, v, t) ~l~v + T(v, x, t) ~lSt be a vector field in the Lagrangiau framework. Then the condition of the invariance of the one-form O with respect to V is given by LvO ~ 0, where Lv(. ) denotes the Lie derivative. When we consider the Hamiltonian formalisms the vector field under consideration takes the form Z = ZI( p, q, t) ~/~p + Z2(p, q, t) ~/~q + Za(p, q, t) 8/~t, and the requirement of the invariance of the one-form ~ with respect to V is given as above by Lz ~ ~ O. We mention that the requirements can be extended slightly. The knowledge of the vector field V and Z leads to the constants of the motion. The purpose of the present paper is twofold. First of all we give the relationship between symmetries and constants of the motion in such a form that we can apply this relationship both in the Lagrangian and in the Hamiltonian framework. Our formulation contains both the relativistic and the nonrelativistic case. Our second aim

A linear Uzawa-algorithm for the steady-state Navier-Stokes problem

Abstract: An Uzawa algorithm of Temam is improved so that the Navier-Stokes boundary value problem is reduced to a sequence of linear Poisson problems. A simple finite element method is shown to give a convergent sequence of approximate solutions. Finally a penalty variant is discussed.

On the asymmetry of the stress tensor of materials with internal degrees of freedom

Abstract: It was first shown by West that the stress tensor in the balance of linear momentum can be chosen to be symmetric. In this paper some consequences of this symmetrization procedure and its physical meaning are studied. On a statistical mechanical basis an asymmetric stress tensor for materials with internal degrees of freedom is derived. Arguments are given that the asymmetric stress tensor has to be preferred to the symmetrized one.

Ein Fourier-Algorithmus für die Anfangswertaufgabe der Dreidimensionalen Wirbeltransportgleichung

Abstract: A Fourier algorithm is given in order to solve the initial value problem to the (suitably modified) equation of transport of vorticity for viscous incompressible fluids in the R3. The algorithm turns out to be stable and convergent with linear convergence velocity. A test problem is elaborated.

Synthesis of multiloop discrite time systems with constraints

Abstract: In this paper it is assumed that apart from the actual controlled varible some inner system variables of a given plant can be applied to produce the manipulated variable. A linear sampled data control system is to be designed so that some system quantities e.g. the manipulated variable and the system error and so on do not exceed given maximum values. Necessary conditions on the controller transfer functions are derived supposing that the absolute values of the system input signals and their rates of change are bounded. The design procedure is carried out computeraided in the transformed frequency domain using nonlinear programming algorithms.