Azacyanines of the Pyrrolopyrrole Series

The reaction of POCl₃‐activated, readily soluble diketopyrrolopyrrole (DPP) with 2‐aminoheteroaromatics to yield 1:1 and 1:2 hydrogen chelates is described. Complexation of these hydrogen chelates with boron reagents results in thermally and photochemically stable fluorescent dyes (PP–azacyanines). The 1:2 complexes in particular absorb at long wavelengths and are brightly fluorescing. The rich photophysics of the new compounds are presented. Both the pronounced vibrational fine structure of the S₀→S₁ transitions and the observed fluorescence phenomena allow detailed conclusions to be made on the correlation between molecular structure and optical properties.     

Exploring the performance of spatial stochastic simulation algorithms

Since the publication of Gillespie’s direct method, diverse methods have been developed to improve the performance of stochastic simulation methods and to enter the spatial realm. In this paper we discuss a spatial τ-leaping variant (Sτ) that extends the basic leap method. Sτ takes reaction and both outgoing and incoming diffusion events into account when calculating a leap candidate. A performance analysis shall reveal details on the achieved success in balancing speed and accuracy in comparison to other methods. However, performance analysis of spatial stochastic algorithms requires significant effort — it is crucial to choose suitable (benchmark) models and to carefully define model and simulation setups that take problem and simulation design spaces into account.     

Coevolutionary motion and swarming in a niche space model of ecological species interactions

Organisms are involved in coevolutionary relationships with their competitors, predators, preys and parasites. In this context, we present a simple model for the co-evolution of species in a common niche space, where the fitness of each species is defined via the network of interactions with all other species. In our model, the sign and type of the pairwise interactions (being either beneficial, harmful or neutral) is given by a pre-determined community matrix, while the interaction strength depends on the niche-overlap, i.e. the pairwise distances between species in niche space. The evolutionary process drives the species toward the places with the higher local fitness along the fitness gradient. This gives rise to a dynamic fitness landscape, since the evolutionary motion of a single species can change the landscape of the others (known as the Red Queen Principle). In the simplest case of only two-species we observe either a convergence/divergence equilibrium or a coevolutionary arms race. For a larger number of species our analysis concentrates on an antisymmetric interaction matrix, where we observe a large range of dynamic behaviour, from oscillations, quasiperiodic to chaotic dynamics. In dependence of the value of a first integral of motion we observe either quasiperiodic motion around a central region in niche space or unbounded movement, characterised by chaotic scattering of species pairs. Finally, in a linear food-chain we observe complex swarming behaviour in which the swarm moves as a whole only if the chain consists of an even number of species. Our results could be an important contribution to evolutionary niche theory.     

Comparison of multi-echo spiral and echo planar imaging in functional MRI

Multi-echo spiral and echo-planar (EPI) imaging sequences were compared in functional imaging experiments at 3 Tesla. Both sequence types allow calculation of the effective transversal relaxation time T(2)* and the initial signal intensity I(0). These parameters can be used in evaluation of the functional signal with respect to inflow effects and other vascular sources. Prior to functional magnetic resonance imaging (fMRI) experiments T(2)* measurements in the human brain were performed with single- and multi-echo FLASH (fast low angle shot) and compared with EPI und spiral imaging sequences. These experiments resulted in T(2)* values ranging from 42.9 to 53.8 ms in a ROI including white and gray matter and CSF in a prefrontal brain region, and allowed validation of the quantitative results of the fast single-shot techniques. In functional experiments with motor stimulation mean absolute T(2)* increases during stimulation of 1.1 +/- 0.6 ms and 1.4 +/- 0.9 ms were found with multi-echo EPI and spiral imaging, respectively, averaged over the activated pixels. In addition, absolute T(2)* values and the size of activated areas obtained with both sequences are comparable. In these investigations spiral imaging allowed higher spatial resolution due to more efficient use of available gradient performance.     

Arch?ometrische Untersuchungen von r?mischen Ziegeln und Wandplatten

Zusammenfassung Am Beispiel von Ziegel- und Wandplattenbruchstücken einer römischen Wüstung bei Schwarzenholz (Saarland) wird die Auswertung der Analysendaten und der Ergebnisse von Schnittbetrachtungen vorgestellt. Als geeignete Analysenverfahren erweisen sich die Röntgenfluorescenzanalyse und die Atomabsorptionsspektralanalyse. Mit Hilfe der Taxometrie gelingt eine Einteilung der Bruchstücke in die Gruppen Örtliches Material, Blickweiler und Gestempeltes Material. Die Untersuchungsergebnisse gestatten die Bestimmung des mengenmäßigen Anteils verschiedener Produktionen für einen Fundplatz und erlauben somit dem Archäologen Aussagen über wirtschaftliche Zusammenhänge.Für finanzielle Unterstützung danken wir der Stiftung Volkswagenwerk, Hannover.     

Austauscher mit cyclischen Polyethern als Ankergruppen—I: Herstellung und Charakterisierung

Numerous exchangers with cyclic polyethers as anchor groups have been prepared and their properties examined. 4-Carboxyethyl- and 4-hydroxypropylbenzo crown ethers were fixed to silica gel and used as stationary phases in high-pressure liquid-chromatography.     

Vergleichende Untersuchungen zur Genauigkeit photometrischer und chemischer Analysenverfahren

Zusammenfassung Wir haben in der vorstehenden Abhandlung zu zeigen versucht, in welcher Weise die Zuverlässigkeit photometrischer Meßeinrichtungen und Meßverfahren zu prüfen ist. Im vorliegenden Fall — beim lichtelektrischen Photometer ELKO II — hat die statistische Prüfung sämtlicher Arbeitsgänge ergeben, daß der Apparatefehler nicht größer ist als der zufällige Fehler bei klassischen chemischen Bestimmungsverfahren. Es ist demnach möglich, mit Hilfe photometrischer Messungen auch bei größeren Substanzmengen zu ebenso genauen und zuverlässigen Resultaten zu gelangen wie mit klassischen Verfahren. Statistisch überprüft und verglichen wurden beim Kupfer die photometrischen Bestimmungen mit Nitrilotriessigsäure und als Kupfersulfat     

Quasiregular concentric waves in heterogeneous lattices of coupled oscillators

We study the pattern formation in a lattice of locally coupled phase oscillators with quenched disorder. In the synchronized regime quasiregular concentric waves can arise which are induced by the disorder of the system. Maximal regularity is found at the edge of the synchronization regime. The emergence of the concentric waves is related to the symmetry breaking of the interaction function. An explanation of the numerically observed phenomena is given in a one-dimensional chain of coupled phase oscillators. Scaling properties, describing the target patterns are obtained.     

Nuclear charge radii of 8,9Li determined by laser spectroscopy

The 2s-->3s transition of (6,7,8,9)Li was studied by high-resolution laser spectroscopy using two-photon Doppler-free excitation and resonance-ionization detection. Hyperfine structure splittings and isotope shifts were determined with precision at the 100 kHz level. Combined with recent theoretical work, the changes in the nuclear-charge radii of (8,9)Li were determined. These are now the lightest short-lived isotopes for which the charge radii have been measured. It is found that the charge radii monotonically decrease with increasing neutron number from 6Li to 9Li.     

Measurement of RLT and ATL in the 4He(e, e’p)3H reaction at pmiss of 130-300 MeV/ c

We have measured the ⁴He(e, ep)³H reaction at missing momenta of 130-300 MeV/c using the three-spectrometer facility at the Mainz microtron MAMI. Data were taken in perpendicular kinematics to allow us to determine the response function R_LT and the asymmetry term A_TL. The data are compared to both relativistic and non-relativistic calculations.