Regularization of bending and crossing white matter fibers in MRI Q-ball fields

In diffusion magnetic resonance imaging with high-angular-resolution diffusion imaging, a set of techniques has become available that allows better acquisition and representation of multidirectional diffusion profiles, e.g., in voxels with crossing, branching and kissing fibers. The poor spatial resolution and low signal-to-noise ratio of the data, particularly when acquired under clinical conditions, prevent tractography algorithms from reliably reconstructing complex white matter structures. With cone-beam regularization, an intervoxel smoothing approach has been described, which, in this article, is refined and adapted to fibers with subvoxel bending. By introducing the concept of asymmetric orientation distribution functions (aODFs), we are able to sharpen diffusion profiles of bending fibers and estimate subvoxel curvature. We also propose a deterministic fiber-tracking algorithm that exploits the enhanced resolution of aODFs. The approach is evaluated quantitatively and compared with state-of-the-art noise-suppression techniques in a study with a biological diffusion phantom. Moreover, we present results from an in vivo study in which we demonstrate the method's ability to optimize tractography of bending fiber pathways of optic radiation.     

Sensitivity analysis using the tangent derivative

Using some equivalent characterizations of Bouligand's tangent cone in metric vector spaces, several properties of the tangent derivative of correspondences between metric vector spaces are derived. These results are applied for the sensitivity analysis of a parametrized vector optimization problem.     

Conformational Dynamics of Sensory Rhodopsin II in Nanolipoprotein and Styrene–Maleic Acid Lipid Particles

Styrene–maleic acid lipid particles (SMALPs) provide stable water‐soluble nanocontainers for lipid‐encased membrane proteins. Possible effects of the SMA‐stabilized lipid environment on the interaction dynamics between functionally coupled membrane proteins remain to be elucidated. The photoreceptor sensory rhodopsin II, NpSRII and its cognate transducer, NpHtrII, of Natronomonas pharaonis form a transmembrane complex, NpSRII₂/NpHtrII₂ that plays a key role in negative phototaxis and provides a unique model system to study the light‐induced transfer of a conformational signal between two integral membrane proteins. Photon absorption induces transient structural changes in NpSRII comprising an outward movement of helix F that cause further conformational alterations in NpHtrII. We applied site‐directed spin labeling and time‐resolved optical and EPR spectroscopy to compare the conformational dynamics of NpSRII₂/NpHtrII₂ reconstituted in SMALPs with that of nanolipoprotein particle and liposome preparations. NpSRII and NpSRII₂/NpHtrII₂ show similar photocycles in liposomes and nanolipoprotein particles. An accelerated decay of the M photointermediate found for SMALPs can be explained by a high local proton concentration provided by the carboxylic groups of the SMA polymer. Light‐induced large‐scale conformational changes of NpSRII₂/NpHtrII₂ observed in liposomes and nanolipoprotein particles are affected in SMALPs, indicating restrictions of the protein's conformational freedom.     

Separation of polar betalain pigments from cacti fruits of Hylocereus polyrhizus by ion-pair high-speed countercurrent chromatography

Polar betacyanin pigments together with betaxanthins from ripe cactus fruits of Hylocereus polyrhizus (Cactaceae) were fractionated by means of preparative ion-pair high-speed countercurrent chromatography (IP-HSCCC) also using the elution–extrusion (EE) approach for a complete pigment recovery. HSCCC separations were operated in the classical ‘head-to-tail’ mode with an aqueous mobile phase. Different CCC solvent systems were evaluated in respect of influence and effectiveness of fractionation capabilities to separate the occurring pigment profile of H. polyrhizus. For that reason, the additions of two different volatile ion-pair forming perfluorinated carboxylic acids (PFCA) were investigated. For a direct comparison, five samples of Hylocereus pigment extract were run on preparative scale (900 mg) in 1-butanol–acetonitrile–aqueous TFA 0.7% (5:1:6, v/v/v) and the modified systems tert.-butyl methyl ether–1-butanol–acetonitrile–aqueous PFCA (2:2:1:5, v/v/v/v) using 0.7% and 1.0% trifluoroacetic acid (TFA) or heptafluorobutyric acid (HFBA) in the aqueous phase, respectively. The chemical affinity to the organic stationary CCC solvent phases and in consequence the retention of these highly polar betalain pigments was significantly increased by the use of the more lipophilic fluorinated ion-pair reagent HFBA instead of TFA. The HFBA additions separated more effectively the typical cacti pigments phyllocactin and hylocerenin from betanin as well as their iso-forms. Unfortunately, similar K_D ratios and selectivity factors α around 1.0–1.1 in all tested solvent systems proved that the corresponding diastereomers, 15S-type pigments cannot be resolved from the 15R-epimers (iso-forms). Surprisingly, additions of the stronger ion-pair reagent (HFBA) resulted in a partial separation of hylocerenin from phyllocactin which were not resolved in the other solvent systems. The pigments were detected by means of HPLC-DAD and HPLC-electrospray ionization–MS using also authentic reference materials.     

Relaxation effects on transverse magnetization using RF pulses long compared to T(2)

The transverse relaxation effects which occur during the application of optimized slice-selective Shinnar-Le Roux pulses are studied. The behavior of both longitudinal and transverse magnetization is examined, focusing the attention on changes which affect the absorption and dispersion components. Besides the reduction in amplitude, the absorption component was found to be unaffected by transverse relaxation times, whereas the dispersion component was strongly distorted. A comparison between the distortion components from pulses having same length but different bandwidths is given.     

Berechnung der Wärmestrahlung in athermanen Medien mittels einer verallgemeinertenn-Flußmethode

Zusammenfassung Zur Beschreibung des Strahlungsenergieaustauschs wird eine systematisch erweiterbaren-Flußmethode entwickelt, die für die Richtungsabhängigkeit der Strahlungsintensität einen Potenzreihenansatz verwendet. Hierdurch sind gegenüber klassischen Flußmethoden die Strahlungsflüsse in verschiedenen Richtungen stärker gekoppelt, und es kann die Flußanzahl unabhängig von der Dimensionalität des Gesamtmodells gewählt werden. Strahlungsberechnungen an eindimensionalen Geometrien zeigen durch Vergleich mit exakten Lösungen die mit der Flußanzahl wachsende Genauigkeit der Methode bei mittleren optischen Dichten bis hin zu einem 9-Flußmodell.

---

Prediction of the thermal radiation in atherm media with an extendablen-flux-method

To describe the exchange of radiation energy has been developed a systematically extendablen-flux-method which copes with the direction-dependency of radiation intensity by using a power series approach. Compared with classical flux-methods there is in this case a stronger linkage among the radiation fluxes in different directions and, moreover, the number of fluxes may be selected irrespective of the dimensionality of the overall model. Radiation calculations on onedimensional geometries have demonstrated, by way of comparison with exact solutions, the increasing accuracy of the method, with medium optical densities, up to a 9-flux-model.

---

Formelzeichen A m² Fläche - e ₁,e ₂,e ₃ Einheitsvektoren - e₁, e₂, e₃ Richtungskosinus - f W/m² sr differentieller, vektorieller Strahlungsfluß - f W/m³ sr spektraler, differentieller, vektorieller Strahlungsfluß - g W/m² skalarer Strahlungsfluß - g W/m³ spektraler, skalarer Strahlungsfluß - h J_s Plancksches Wirkungsquantum - i W/m² sr Strahlungsintensität - g _b W/m³ sr spektrale Strahlungsintensität eines - i _ij W/m² sr Intensitätskoeffizienten - i W/m³ sr spektrale Strahlungsintensität - k J/K Boltzmann-Konstante - L m Spaltbreite - R m Zylinderradius - r={r,, z} m Ortsvektor - T K Temperatur - _w, _w Absorptions-, Emissionsgrad der Wand - =r/R norm. radiale Koordinate - _A , _S m^–1 Absorptions-, Streukoeffizient - _A, , _S, m^–1 spektraler Absorptions-, Streukoeffizient - m Wellenlänge - =2z/L norm, axiale Koordinate - ₀=_A L/2 optische Dichte - ₀= _A R optische Dichte - W/m² K⁴ Stefan-Boltzmann-Konstante - _s W/m² Strahlungsfluß - ={, } Richtungseinheitsvektor - _n Normaleneinheitsvektor an der Wand Indizes W Wand - + vorwärtig - – rückwärtig     

Effect of Dimethyl Carbonate on the Dynamic Properties and Ionicities of Ionic Liquids with [MIII(hfip)4]− (M=B,Al) Anions

Several ionic liquids (ILs) comprising [B(hfip)₄]^? [hfip=OCH(CF₃)₂] or [Al(hfip)₄]^? anions and imidazolium or ammonium cations were prepared and mixed with up to 270 mol % of dimethyl carbonate (DMC). The viscosities, conductivities, and self‐diffusion constants of these mixtures and, where possible, of the neat ILs were measured and compared with common [NTf₂]^? based ILs and their mixtures with DMC. A tremendous decrease of the viscosities and a likewise increase of the conductivities and diffusion constants can be achieved for all classes of ILs. However, the order of the conductivities is partially reversed in the diffusion data. This is probably due to the low dielectric constant of DMC and the, thus, favored ion pairing, as evidenced, for example, by the calculated ionicities. Altogether, our data show that the chemically robust, but high‐melting and more viscous [B(hfip)₄]^? ILs might be candidates for electrolytes when mixed with suitable molecular solvents.