Actively shaped supercontinuum from a photonic crystal fiber for nonlinear coherent microspectroscopy

The combination of broadband pulses from a photonic crystal fiber (PCF) pumped by a standard 100 fs oscillator and pulse shaping is successfully employed for coherently controlled nonlinear spectroscopy. The pulse shaper manages not only to compress the PCF supercontinuum in a closed-loop optimization scheme but also to manipulate the phase at the same time for quantum control applications. This approach is demonstrated by single-beam coherent anti-Stokes Raman microspectroscopy and should be, due to its simplicity, well suited for general applications in nonlinear microscopy.     

Rank deficiency and superstability of hybrid systems

The objectives of this paper are to study the rank properties of flows of hybrid systems, show that they are fundamentally different from those of smooth dynamical systems, and to consider applications that emphasize the importance of these differences. It is well known that the flow of a smooth dynamical system has rank equal to the space on which it evolves. We prove that, in contrast, the rank of a solution to a hybrid system, a hybrid execution, is always less than the dimension of the space on which it evolves and in fact falls within possibly distinct upper and lower bounds that can be computed explicitly. The main contribution of this work is the derivation of conditions for when an execution fails to have maximal rank, i.e., when it is rank deficient. Given the importance of periodic behavior in many hybrid systems applications, for example in bipedal robots, these conditions are applied to the special case of periodic hybrid executions. Finally, we use the rank deficiency conditions to derive superstability conditions describing when periodic executions have rank equal to 0, that is, we determine when the execution is completely insensitive to perturbations in initial conditions. The results of this paper are illustrated on three separate applications, two of which are models of bipedal walking robots: the classical single-domain planar compass biped and the two-domain planar kneed biped.     

Efficiency by trust in fairness? multiperiod ultimatum bargaining experiments with an increasing cake

Previous ultimatum bargaining experiments have shown that bargainers face the conflict whether to exploit bargaining power or to comply with basic norms of distributive justice. In multiperiod ultimatum bargaining for an increasing cake, trust in fairness can enable cooperation and thus more efficient results but is also open to opportunistic exploitation. In such a game the two players take turns in being the one who suggests an agreement and decides whether this is the final proposal, whereas his partner can only accept this proposal or reject it. While the game theoretic solution implies an immediate agreement assigning nearly all the cake to the demanding player, efficiency requires to postpone the agreement to the last possible round. Our 2 × 2-factorial design varies the number of possible bargaining periods and the cake increase, allowing us to explore several hypotheses.     

Geminal bis-ureas as gelators for organic solvents: gelation properties and structural studies in solution and in the gel state

Several geminal bis-urea compounds were synthesised by means of an acid-catalysed condensation of various benzaldehydes with different monoalkylureas. Many of these compounds form thermoreversible gels with a number of organic solvents at very low concentrations (<3mM) and which are stable to temperatures higher than 100 degrees C. Electron microscopy revealed a three-dimensional (3D) network of intertwined fibres, which are several tens of micrometers long and have a width ranging from approximately 30 to 300 nm. The possible aggregate forms and aggregate symmetries were evaluated by means of molecular mechanics calculations. 1H NMR, 2D NMR, 13C NMR and 13C-CP/MAS NMR techniques were used to obtain information about the aggregation and possible aggregate symmetry of geminal bis-ureas in solution, in the gel state, and in the solid state.     

Long-range sigma-pi interactions in tetrahydro-4H-thiopyran end-capped oligo(cyclohexylidenes). Photo-electron spectroscopy, ab initio SCF MO calculations, and natural bond orbital analyses

Long-range sigma-pi interactions in tetrahydro4H-thiopyran end-capped oligo(cyclohexylidenes) were identified by He(I) photoelectron spectroscopy (PES) and ab initio RHF/6-31G* calculations. The vertical ionization energies Ivj of the highest occupied molecular orbitals (MO's) were assigned using Koopmans' theorem (Iv,j = -epsilonj) and by correlation with the ionizations of related reference compounds. The experimental (PES) and theoretical (RHF/6-31G*) results are in good agreement. For tercyclohexylidene derivatives which contain two nonconjugated pi-bonds splittings deltaIv,j of the pi-bands in the range from approximately 0.5 to 0.7 eV (delta-epsilonj approximately 0.6 to 0.9 eV). For the bi- and tercyclohexylidene compounds containing two sulfur atoms at their alpha- and omega-end positions the pi-type sulfur lone pair bands [Lppi(S)] split significantly by deltaIvj approximately 0.3 to 0.4 eV (delta-epsilonj approximately 0.3 to 0.4 eV), i.e. sigma-pi interactions over distances of ca. 8 and 12 A, respectively, occur. The magnitude of the interactions and the observed splittings are independent of the anti and syn conformations of the oligo(cyclohexylidene) hydrocarbon skeletons. RHF/6-31G* Natural Bond Orbital analyses reveal that the Hax-C-C-Hax precanonical MO's (PCMO's) centered on the cyclohexyl-type rings are paramount for the relay of the through-bond sigma-pi interactions; no through-space sigma-pi interactions were identified.     

Microscopic order and disjoining pressure in lipid films

It is demonstrated how, in a plane film at small film thickness, the orientational order of the hydrocarbon segments of the molecules present in lipid films translates into an increase of the macroscopic normal stress from the film meniscus (film-forming bulk phase) to the proper film phase.     

Performance of a fast fiber based UV/Vis multiwavelength detector for the analytical ultracentrifuge

The optical setup and the performance of a prototype UV/Vis multiwavelength analytical ultracentrifuge (MWL-AUC) is described and compared to the commercially available Optima XL-A from Beckman Coulter. Slight modifications have been made to the optical path of the MWL-AUC. With respect to wavelength accuracy and radial resolution, the new MWL-AUC is found to be comparable to the existing XL-A. Absorbance accuracy is dependent on the light intensity available at the detection wavelength as well as the intrinsic noise of the data. Measurements from single flashes of light are more noisy for the MWL-AUC, potentially due to the absence of flash-to-flash normalization in the current design. However, the possibility of both wavelength and scan averaging can compensate for this and still give much faster scan rates than the XL-A. Some further improvements of the existing design are suggested based on these findings.