Fak. 2 Mathematik und Naturwissenschaften

1906 Items

Recent Submissions
Modeling and simulation of electrically driven quantum dot based single-photon sources

Kantner, Markus (2018)

Semiconductor quantum optics is on the leap from the lab to real world applications. The currently unfolding "second quantum revolution" aims at the development of novel quantum technologies that exploit inherent quantum mechanical phenomena like entanglement and quantum superposition for communication and information processing tasks. Many applications, such as eavesdropping-secure encryption ...

Optical gain and modal loss in AlGaN based deep UV lasers

Martens, Martin Georg Rudolf (2018)

Because of its direct bandgap covering the ultraviolet (UV) spectral region from 360 nm to 200 nm, the AlGaN material system is a promising candidate for the realization of deep UV laser diodes emitting below 300 nm, being an alternative for bulky and energy consuming excimer or frequency multiplied lasers. Possible applications cover e.g. medical detection, gas sensing, material processing, ...

Remarks on thermodynamical terminology

Muschik, Wolfgang (2004)

Often difficulties in understanding thermodynamics arise from using different terminology or semantics. Therefore here some few remarks are made for tending towards a unified thermodynamical terminology.

Thermodynamic interaction between two discrete systems in non-equilibrium

Muschik, Wolfgang ; Berezovski, Arkadi (2004)

A systematic description of the interaction between two systems is presented within the framework of thermodynamics of discrete systems. We distinguish between two situations: a contact between an equilibrium system and a non-equilibrium one, and a contact between two non-equilibrium systems. In the second case the state space includes replacement quantities, which reduce the situation to a con...

Mesoscopic theory of liquid crystals

Muschik, Wolfgang ; Papenfuss, Christina ; Ehrentraut, Harald (2004)

Liquid crystals of uniaxial and biaxial molecules are considered in the framework of the mesoscopic description which is a general tool of continuum theory. A mesoscopic theory introduces the fields beyond hydrodynamics as additional variables of a configuration space, called mesoscopic space, on which the fields appearing in balances are defined. Besides the mesoscopic space, a mesoscopic dist...

Fragmentable Heterogeneous Cocatalysts for the Metallocene-Catalyzed Polymerization of Olefins, I. Surface Modification of Silica and Characterization of the Resulting Carriers

Schumann, Herbert ; Widmaier, Ralf ; Lange, Katharina C. H. ; Wassermann, Birgit C. (2005)

Surface modification of pre-dried spherical silica nano-particles with diameters of 235 nm and 10 to 20 nm and of commercially available non-spherical silica materials using various aminoalkyltrialkoxysilanes and α-ω-bis(alkoxysilyl)organyls (organyl = alkanediyl, aminoalkanediyl, polyether, polysiloxane) has been performed in suspension in solvents with water. The quantity of water has a domin...

Fragmentable Heterogeneous Cocatalysts for the Metallocene-Catalyzed Polymerization of Olefins, II [1]. Preparation, Characterization and Testing of the Cocatalysts and Microscopic Evaluation of the Polyethylene

Schumann, Herbert ; Widmaier, Ralf ; Lange, Katharina C. H. ; Wassermann, Birgit C. (2005)

Surface modified silica were reacted with different aluminiumalkyls AlR2R’ (R = Me, Et, i-Bu, R’ = H, Me, Et, i-Bu), oligomeric methylaluminoxane (MAO) and combinations of both, to yield heterogeneous cocatalysts. These cocatalyts were employed to polymerize ethylene using zirconocene dichloride as the catalyst. The polymerization activity profiles have been recorded and compared with the infor...

2,5-Dimethyl-3,6-bis[(2,6-diisopropylphenylimino)methyl]- and 2,6-Bis[(2,6-diisopropylphenylimino)methyl]pyrazine: Two New Chelating Ligands for Transition Metal Complexes

Schumann, Herbert ; Luo, He-Kuan (2005)

The reaction of tetramethylpyrazine with SeO2 yields 2,5-dimethylpyrazine-3,6-dicarboxaldehyde (1) from which the 2,5-dimethyl-3,6-bis[(2,6-diisopropylphenylimino)methyl]pyrazine (2) was synthesized by treatment with 2 equivalents of 2,6-diisopropylaniline. 2,6-Dimethylpyrazine reacts with benzaldehyde to give 2,6-distyrylpyrazine (3). Ozonolysis of 3, followed by treatment with Na2SO3 and 2,6-...

Di-, Hexa- und Deca-substituierte Decaphenylferrocene

Schumann, Herbert ; Sühring, Klaudia (2005)

5-Bromo-1,2,3,4-tetraphenyl-5-p-tolyl-1,3-cyclopentadiene (1a), 5-Bromo-1,4-di-phenyl-2,3,5- tri-p-tolyl-1,3-cyclopentadiene (1b), 5-Bromo-1,2,3,4,5-penta-p-tolyl-1,3-cyclopentadiene (1c), 5- Bromo-1,2,3,4-tetraphenyl-5-p-bromophenyl-1,3-cyclopentadiene (1d), and 5-Bromo-1,2,3,4-tetraphenyl- 5-p-anisyl-1,3-cyclopentadiene (1e) react with ironpentacarbonyl in m-xylene to yield the corresponding ...

Metallkomplexe von 2,2’-Dipyridyldisulfid mit Quecksilber(II)-, Cadmium(II)- und Zink(II)-Halogeniden und mit Cadmium(II)- Trifluormethansulfonat

Pickardt, Joachim ; Chrzanowski, Lars von ; Steudel, Ralf ; Borowski, Marina ; Beck, Sebastian (2005)

Crystals of diiodo-2,2’-dipyridyldisulfide mercury(II) [HgI2(C5H4N)2S2], dichloro-2,2’-dipyridyldisulfide zinc(II) [ZnCl2(C5H4N)2S2], dibromo-2,2’-dipyridyldisulfide cadmium(II) [CdBr2 (C5H4N)2S2], diiodo-2,2’-dipyridyldisulfide cadmium(II) [CdI2(C5H4N)2S2], and diaquo 2,2’-dipyridyldisulfide cadmium(II) trifluoromethanesulfonate [Cd(H2O)2(C5H4N)2S2](CF3SO3)2, were obtained by evaporation of so...

Studies on the Thermolysis of Ether-Stabilized Lu(CH2SiMe3)3. Molecular Structure of Lu(CH2SiMe3)3(THF)(diglyme)

Rufanov, Konstantin A. ; Freckmann, Dominique M. M. ; Kroth, Heinz-Jürgen ; Schutte, Stefan ; Schumann, Herbert (2005)

Lu(CH2SiMe3)3(THF)2 (2) decomposes slowly at room temperature with formation of Me4Si. In order to understand the mechanism of this elimination process, Lu(CH2SiMe3)3([D8]-THF)2 (1), Lu(CH2SiMe3)3(THF)(DME) (3), and Lu(CH2SiMe3)3(THF)(diglyme) (4) were prepared. The results of 1H NMR spectroscopic studies of the decomposition in solution exclude an α- as well as a β -H elimination mechanism and...

Deca(4-methylbenzyl)ferrocen und -stannocen

Schumann, Herbert ; Sühring, Klaudia ; Weimann, Roman ; Hummert, Markus (2005)

Cyclopentadiene reacts with five equivalents of 4-methylbenzylalcohol (1:5,6 mole ratio) and sodium yielding penta(4-methylbenzyl)cyclopenta-2,4-diene (1), which upon treatment with butyl lithium affords the lithium salt [(4-MeC6H4CH2)5C5]Li (2). The reactions of 2 with FeCl2 and SnCl2 result in the formation of deca(4-methylbenzyl)ferrocene (3) and deca(4-methylbenzyl)stannocene (4), respectiv...

Flow Velocity and Effective Viscosity of a Fluid Containing Rigid Cylindrical Inclusions

Hess, Siegfried (2005)

The determination of the flow properties of a fluid containing a cylindrical inclusion with its long axis oriented parallel to the vorticity direction is a 2-dimensional problem which is treated as a special case in a calculation of the corresponding D-dimensional problem. The velocity and pressure are obtained from the solution of the equations of hydrodynamics where D-dimensional multipole po...

Close-to-Fourier heat conduction equation of solids of constant mass density

Muschik, Wolfgang ; Siebert, Jürgen ; Herrmann, Heiko ; Rückner, Gunnar (2005)

Heat conduction close-to-Fourier means that we look for a minimal extension of heat conduction theory using the usual Fourier expression of the heat flux density and modifying that of the internal energy as minimally as possible by choosing the minimal state space. Applying Liu's procedure results in the class of materials and a dierential equation both belonging to the close-to-Fourier case of...

Supraconvergence of a Finite Difference Scheme for Elliptic Boundary Value Problems of the Third Kind in Fractional Order Sobolev Spaces

Emmrich, Etienne ; Grigorieff, Rolf Dieter (2006)

In this paper, we study the convergence of the finite difference discretization of a second order elliptic equation with variable coefficients subject to general boundary conditions. We prove that the scheme exhibits the phenomenon of supraconvergence on nonuniform grids, i.e., although the truncation error is in general of the first order alone, one has second order convergence. All error esti...

Introduction of Substituents on the 2-Oxo-piperazine Skeleton by [3+2] Cycloaddition and Subsequent Transformation

Wierschem, Frank ; Rück-Braun, Karola (2006)

The 3,4-substituted 2-oxo-piperazines 5 - 9 are obtained by [3+2] cycloaddition from nitrone 1 and a variety of alkenes. Subsequent functionalization of the bicyclic adducts involves reductive N-O bond cleavage. A route towards libraries of immobilized 1,3-aminoalcohols with a 3,4-substituted 2-oxo-piperazine scaffold is briefly discussed for adducts derived from N-substituted maleic imides

Structure-Activity Relationships of Synthetic Analogs of Jasmonic Acid and Coronatine on Induction of Benzophenanthridine Alkaloid Accumulation in Eschscholzia californica Cell Cultures

Haider, Georg ; Schrader, Thomas von ; Füßlein, Martin ; Blechert, Siegfried ; Kutchan, Toni M. (2000)

A facile test system based on the accumulation of benzo[c]phenanthridine alkaloids in Eschscholzia californica cell suspension culture (an indicator of defense gene activation) has been used to analyze a series of synthetic compounds for elicitor-like activity. Of the 200 jasmonic acid and coronatine analogs tested with this system, representative results obtained with 49 of them are presented ...

Fluorite-Type Solid Solutions in the System Y-Ta-O-N: A Nitrogen-Rich Analogue to Yttria-Stabilized Zirconia (YSZ)

Schilling, H. ; Wolff, H. ; Dronskowski, Richard ; Lerch, Martin (2006)

Fluorite-type phases in the system Y-Ta-O-N have been prepared by ammonolysis of Y-Ta-O precursors. X-ray powder patterns show unusual asymmetrical reflection profiles explained by DFT and MD methods. The anion vacancy concentration of some of these oxynitrides is similar to that of yttria-doped zirconia, commercially used as solid electrolyte in fuel cells. Hence, these compounds are interesti...

Kann die Physik das Leben wissenschaftlich erfassen?

Borzeszkowski, Horst-Heino von (2006)

Oft wird die in der Überschrift gestellte Frage kurz und bündig mit dem Satz beantwortet: »Natürlich nicht,denn Physik ist nicht Biologie!« Im hiesigen Kontext wiegt allerdings schwerer, daß Hegel ebenfalls zu einer verneinenden Antwort auf diese Frage kommt. Um Hegels Argumente hinsichtlich ihrer Stichhaltigkeit zu analysieren, hat man nicht eine Gegenüberstellung dessen, was wir heute unter P...

Radii minimal projections of polytopes and constrained optimization of symmetric polynomials

Brandenberg, René ; Theobald, Thorsten (2006)

We provide a characterization of the radii minimal projections of polytopes onto j-dimensional subspaces in Euclidean space . Applied to simplices this characterization allows to reduce the computation of an outer radius to a computation in the circumscribing case or to the computation of an outer radius of a lower-dimensional simplex. In the second part of the paper, we use this characterizati...