Ein Interferometer für langsame Neutronen

After discussing the feasibility and possible usefulness of a neutron interferometer, we describe an arrangement whereby Fresnel interferences have been obtained for neutrons with wavelengths of about 4.4 Å in a 10 meter flight path with a 0.01 mm entrance slit, using two glass prisms instead of the Fresnel biprism. A useful separation of the two coherent beams of 0.06 mm has been reached. Possible improvements of the method are discussed.     

Development,standardization and refinement of procedures for evaluating effects of endocrine active compounds on development and sexual differentiation of <Emphasis Type="Italic">Xenopus laevis</Emphasis>

Xenopus laevis has been introduced as a model to study effects of endocrine-active compounds (EAC) on development and sexual differentiation. However, variable and inconsistent data have raised questions about the reliability of the test methods applied. The current study was conducted in two laboratories to develop, refine, and standardize procedures and protocols. Larvae were exposed in flow-through systems to 17β-estradiol (E2), at concentrations from 0.2 to 6.0 μg E2 L⁻¹ in Experiment 1A, and 0.015 to 2.0 μg E2 L⁻¹ in Experiment 1B. In both studies survival (92%, 99%) and percentage of animals that completed metamorphosis (97%, 99%) indicated reproducible biological performance. Furthermore, minor variations in husbandry led to significant differences in snout-to-vent length, weight, and gonad size. In Experiment 1A, almost complete feminization occurred in all E2 treatment groups whereas a concentration response was observed in Experiment 1B resulting in an EC₅₀ of 0.12 μg E2 L⁻¹. The final verified protocol is suitable for determining effects of EAC on development and sexual differentiation in X. laevis.     

Der Einfluß der Koordinationssphäre von Samarocenen auf die Synthese von flüssigkristallinen Polymethacrylaten

The Influence of the Coordination Sphere of Samarocenes on the Synthesis of Liquid Crystalline Polymethacrylates (C₅Me₅)₂Sm(THF)₂ ( 1 ) reacts with 1,3‐Diisopropyl‐4,5‐dimethylimidazoline‐2‐ylidene C₃N₂Me₂iPr₂ (iPr‐carben) with formation of (C₅Me₅)₂Sm(iPr‐carben) ( 3 ). The reaction of (C₅Me₄Et)₂Sm(THF)₂ ( 2 ) with Al₂Me₆ in toluene yields [(C₅Me₄Et)₂Sm(CH₃)Al(CH₃)₃]₂ ( 6 ). 3 and 6 were characterized by single crystal X‐ray structure analysis. Via living polymerization of mesogenic methacrylates with the organosamarium complexes 1 , 2 , 3 , (C₅Me₅)₂Sm(C₃H₅) ( 4 ), (C₅Me₅)₂Sm(CH₃)(THF) ( 5 ), 6 , and (C₅Me₄Et)₂SmCH(SiMe₃)₂ ( 7 ), liquid crystalline homo‐ and blockcopolymers were obtained with narrow molecular mass distribution indexes in high yield. Partial competitive mechanisms are observed dependend of the structure of the catalyst and the polarity of the solvents.     

Gas transport properties of soluble poly(phenylene sulfone imide)s

Gas transport of helium, hydrogen, carbon dioxide, oxygen, argon, nitrogen, and methane in three soluble poly(phenylene sulfone imide)s based on 2,2-bis(3,4-decarboxyphenyl) hexafluoropropane dianhydride (6FDA) has been investigated. The effects of increasing length of well-defined oligo(phenylene sulfone) units on the gas permeabilities and diffusivities were determined and correlated with chain packing of the polymers. Activation energies of diffusion and permeation were calculated from temperature-dependent time-lag measurements. The influences of the central group in the diamine moiety of 6FDA-based polyimides on physical and gas transport properties are discussed. The incorporation of a long oligo(phenylene sulfone) segment in the polymer backbone decreases gas permeability and permselectivity simultaneously. The decreases in permeability coefficients can be mainly related to decreases in diffusion coefficients. Changing the central group of diamine moiety from  S to  SO₂ leads to a 45–50% decrease in CO₂ and O₂ permeabilities without appreciable increase in the selectivities. This is considered to be due to the formation of charge transfer complexes. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 1855–1868, 1997     

Novel study on the liquid crystalline behavior of poly(methacrylate)s with biphenyl side groups

We report the synthesis and characterization of a series of liquid crystalline polymers substituted with the 4′-methoxybiphenyl-4-yloxy group. The spacer length is varied from 4–8 methylene units. The materials are characterized by polarized light microscopy, differential scanning calorimetry, and X-ray analysis. All homologues show highly ordered phases. Additionally, the butylene polymer shows a broad nematic mesophase. For the first time, the narrow nematic phase of the hexylene homologue could be confirmed experimentally. X-ray analysis of the polymers made exact assignments of the low temperature phases possible, thus giving access to the analysis of the arrangement of the mesogenes within the layers. The pentylene homologue shows a distinct deviation from the behavior of the other polymers. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2669–2679, 1998     

Mesophase structure and alignment under different fields of liquid crystalline main-chain/side-group block copolymers

Liquid crystalline block copolymers are new materials in which multiple molecular interactions can provide the driving force for complex phase behaviors and states of order. Block copolymers containing both liquid crystalline main-chain polyester and side-group polymethacrylate blocks were investigated. They phase separated in the liquid crystalline state and their individual mesophases coexisted. The copolymers responded very differently when either a mechanical or a magnetic field was used for alignment. In the fibers the orientations of the side-group and main-chain smectic planes with respect to the fiber axis depended critically on the block lengths and on their distinct tendencies to align, whereas under a magnetic field the mesogens aligned collectively with their long molecular axis parallel to the field, independent of the copolymer structure.     

The exotic nilcone of a symplectic group

Let G be the symplectic group $S{p}_{2n}(k)$ (k an algebraically closed field of characteristic ≠2). It acts in $V=k^{2n}$. The exotic nilcone of G is the nilcone, in the sense of invariant theory, of the G-module $V\times {\wedge }^{2}V$. The paper discusses elementary properties of the G-action on the exotic nilcone.     

Structure elucidation of cyclic pyoverdins and examination of rearrangement reactions in MS/MS experiments by determination of exact product ion masses

Structure elucidation of naturally occurring linear and cyclic peptidic compounds can be complicated by rearrangement reactions induced upon collision activation (CA) when parts of the molecule migrate, suggesting incorrect substitution patterns. Such complex rearrangements are examined and discussed for two iron complexing compounds produced by the bacterial genus Pseudomonas (so-called pyoverdins). Various MS2- and MS3-product ion experiments were performed using a quadrupole-ion trap (QIT) at low resolution and a FT-ICR at high resolution allowing accurate mass determinations. The results of the multidimensional study confirm the proposed processes. On the basis of the series of tandem-MS experiments the structure of a new pyoverdin from a P. fluorescens strain [PVD(D47)] is deduced.     

Active flow control on a 1:4 car model

Lift and drag of a passenger car are strongly influenced by the flow field around its rear end. The bluff body geometry produces a detached, transient flow which induces fluctuating forces on the body, affecting the rear axle, which may distress dynamic stability and comfort significantly. The investigations presented here deal with a 1:4 scale model of a simplified test car geometry that produces fluctuating lift and drag due to its strongly rounded rear geometry. To examine the influence of active flow control on this behavior, steady air jets were realized to exhaust from thin slots across the rear in three different configurations. Investigations were performed at $Re = 2.1 \times 10^{6}$ and included the capturing of effective integral lift and drag, velocity measurements in the surrounding flow field with Laser Doppler Anemometry, surface pressure measurements and surface oil flow visualization on the rear. The flow field was found to be dominated by two longitudinal vortices, developing from the detachment of the flow at the upper C-pillar positions, and a recirculating, transverse vortex above the rear window. With an air jet emerging from a slot across the surface right below the rear window section, tangentially directed upstream toward the roof section, total lift could be reduced by more than 7 %, with rear axle lift reduction of about 5 % and negligible drag affection ( $<$ 1 %).