SEC‐MR‐NMR: Online Coupling of Size Exclusion Chromatography and Medium Resolution NMR Spectroscopy

Online coupling of size exclusion chromatography together with medium resolution nuclear magnetic resonance (SEC‐MR‐NMR) might be one solution to the problem of chemically sensitive detection in liquid polymer chromatography. By use of a combination of SEC with a table‐top, specially designed 20 MHz NMR spectrometer, based on a permanent magnet, online ¹H NMR spectra of SEC fractions can be obtained. The integration of digital filters, mechanical shims and electronic shims led to substantially improved sensitivity and chemical selectivity compared to former TD (time domain) 20 MHz instruments. ¹H NMR spectra of PMMA and PS homopolymers as well as PS‐PMMA block copolymers were of sufficient quality to enable detection and de‐formulation of unknown polymer compounds. ¹H NMR spectra of acceptable resolution and S/N ratio were collected online during the chromatography. The SEC separation online with the NMR measurements performed well and resulted in the proof of principle of the SEC‐MR‐NMR combination.

     

Multifractal description of wind power fluctuations using arbitrary order Hilbert spectral analysis

The objectives are to study and model the aggregate wind power fluctuations dynamics in the multifractal framework. We present here the analysis of aggregate power output sampled at 1 Hz during three years. We decompose the data into several Intrinsic Mode Functions (IMFs) using Empirical Mode Decomposition (EMD). We use a new approach, arbitrary order Hilbert spectral analysis, a combination of the EMD approach with Hilbert spectral analysis (or Hilbert–Huang Transform) and the classical structure-function analysis to extract the scaling exponents or multifractal spectrum ζ(q)$\zeta \left(q\right)$: this function provides a full characterization of a process at all intensities and all scales. The application of both methods, i.e. structure-function and arbitrary-order Hilbert spectral analyses, gives similar results indicating that the aggregate power output from a wind farm, possesses intermittent and multifractal properties. In order to check this result, we generate stochastic simulations of a Multifractal Random Walk (MRW) using a log-normal stochastic equation. We show that the simulation results are fully compatible with the experimental results.     

AFM in Organic Solid State Reactions

Abstract

Organic solid-state reactions are probed with the atomic force microscope (AFM). In all cases phase rebuilding gives rise to characteristic submicroscopic features which change in shape due to phase transformation in later stages of the chemical reaction. Photo-(E/Z)-isomerization of olefin 1 occurs in the crystal, photodimerization of 9-chloroanthracene 3 is used as a probe for characterizing the luminosity distribution of SNOM-tips. Gas/solid imbibition in chiral host 5 proceeds enantiospecifically. Histidine crystals form the dihydrochloride with HC1, ammonia and methylamine react face-selectively with crystalline adipic acid 8, furane-2-carboxylic acid 10 and 2-mercaptobenzothiazole 12. Crystals of olefin 14 add chlorine. Solid-state diazotations and subsequent transformations of the solid diazonium nitrates into triazenes occur quantitatively. Solid/solid pinacol- and benzilic acid rearrangements are probed with the AFM. The features formed by long range molecular movements relate to the crystal packing and are thus different on different faces. Correlations with X-ray structural data are demonstrated. All reactions proceed to completion on a preparative scale and do not produce wastes as do their less selective counterparts if performed in solution.     

Measurement and decomposition of periodic flow structures downstream of a test turbine

The temperature dissipation rate inferred from the balance of $\overline{\theta^{2}}/2$ budget is used for the purpose of studying different methods employed to directly measure dissipation. The terms involved in the budget equation of temperature variance are measured with laser Doppler velocimetry and cold-wire thermometry used simultaneously. This study focuses on the centerline of a turbulent round jet, in the far field, at high Reynolds number (x/D = 30, Re _D  = 1.5 × 10⁵ and Re _λ  = 548). Particular attention is devoted to statistical convergence of second- and third-order moments of velocity and temperature fluctuations. Temperature dissipation obtained by Taylor’s hypothesis and radial temperature derivative spectra confirm local isotropy. A high level of low wave number content is reported for the longitudinal derivative spectra, probably due to transverse mode spectral aliasing and noise contamination for small wire separation. A parallel is drawn between finite difference formulations and the behavior of the autocorrelation coefficient for small wire separations. The temperature dissipation estimates found are close to the budget reference value, but spectral analysis cast doubts on the validity of the streamwise derivative obtained with a pair of probes.     

Raman‐Spektroskopie. Biomedizinische Diagnostik

Raman microspectroscopy has established itself in the last years as an extremely capable analytical method for biomedical diagnosis because it is labelfree and provides high molecular selectivity. That way Raman microspectroscopy allows for a fast identification and characterization of microorganisms like e.g. pathogens on a single cell level. Linear Raman spectroscopy and non‐linear Raman techniques like CARS microscopy have great potential for an objective evaluation of cells or tissue for an early diagnosis of diseases like e.g. cancer.     

On the Euler characteristic of Kronecker moduli spaces

Combining the MPS degeneration formula for the Poincaré polynomial of moduli spaces of stable quiver representations and localization theory, it turns that the determination of the Euler characteristic of these moduli spaces reduces to a combinatorial problem of counting certain trees. We use this fact in order to obtain an upper bound for the Euler characteristic in the case of the Kronecker quiver. We also derive a formula for the Euler characteristic of some of the moduli spaces appearing in the MPS degeneration formula.     

A crystal plasticity framework based on the Continuum Dislocation Dynamics theory: relaxation of an idealized micropillar

The motion and interaction of dislocation lines are the physical basis of the plastic deformation of metals. Although ‘discrete dislocation dynamic’ (DDD) simulations are able to predict the kinematics of dislocation microstructure (i.e. the motion of dislocations in a given velocity field) and therefore the plastic behavior of crystals in small length scales, the computational cost makes DDD less feasible for systems larger than a few micro meters. To overcome this problem, the Continuum Dislocation Dynamics (CDD) theory was developed. CDD describes the kinematics of dislocation microstructure based on statistical averages of internal properties of dislocation systems. In this paper we present a crystal plasticity framework based on the CDD theory. It consists of two separate parts: a classical 3D elastic boundary value problem and the evolution of dislocation microstructure within slip planes according to the CDD constitutional equations. We demonstrate the evolution of dislocation density in a micropillar with a single slip plane. (© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)