Improved B0 field map estimation for high field EPI

Echo planar imaging (EPI) is an ultrafast magnetic resonance imaging (MRI) technique that allows one to acquire a 2D image in about 100 ms. Unfortunately, the standard EPI images suffer from substantial geometric distortions, mainly originating from susceptibility differences in adjacent tissues. To reduce EPI distortions, correction methods based on a field map, which is a map of the off-resonance frequencies, have been developed. In this work, a nonlinear least squares estimator is used to optimize the estimation of the field map of the B₀ field. The model of the EPI and reference data includes parameters for the phase evolution, the complex magnitude, the relaxation of the MRI signal and the EPI-specific phase difference between odd and even echoes, and from these parameters, additional corrections might be computed. The reference data required to estimate the field map can be acquired with a modified EPI-sequence. The proposed method is tested on simulated as well as experimental data and proves to be significantly more robust against noise, compared to the previously suggested method.     

On the ν1/2 ν2 Resonance in the Complex of Carbon Dioxide with Dimethyl Ether

Infrared and Raman spectra of solutions in liquid argon and krypton containing dimethyl ether or its fully deuterated isotopomer and ¹²CO₂ or ¹³CO₂ are investigated. The spectra lead to new data on the ν₁/2 ν₂ resonances appearing in the complex of CO₂ with the ether. The experimental data, and their interpretation, is supported by MP2/6‐311++G(2d,2p) calculations of the cubic and quartic force constants and of the first and higher order dipole moment derivatives required for the modelling of the Fermi and Darling‐Dennison resonances observed.     

Accurate and unbiased estimation of power-law exponents from single-emitter blinking data

Single emitter blinking with a power-law distribution for the on and off times has been observed on a variety of systems including semiconductor nanocrystals, conjugated polymers, fluorescent proteins, and organic fluorophores. The origin of this behavior is still under debate. Reliable estimation of power exponents from experimental data is crucial in validating the various models under consideration. We derive a maximum likelihood estimator for power-law distributed data and analyze its accuracy as a function of data set size and power exponent both analytically and numerically. Results are compared to least-squares fitting of the double logarithmically transformed probability density. We demonstrate that least-squares fitting introduces a severe bias in the estimation result and that the maximum likelihood procedure is superior in retrieving the correct exponent and reducing the statistical error. For a data set as small as 50 data points, the error margins of the maximum likelihood estimator are already below 7%, giving the possibility to quantify blinking behavior when data set size is limited, e.g., due to photobleaching.     

Fluorogenic phospholipid substrate to detect lysophospholipase D/autotaxin activity

[reaction: see text] Lysophospholipase D (lysoPLD), also known as autotaxin (ATX), is an important source of the potent mitogen lysophosphatidic acid (LPA). Two fluorogenic substrate analogues for lysoPLD were synthesized in nine steps from (S)-PMB-glycerol. The substrates (FS-2 and FS-3) show significant increases in fluorescence when treated with recombinant ATX and have potential applications in screening for this emerging drug target.     

Using shared sell-through data to forecast wholesaler demand in multi-echelon supply chains

Operational forecasting in supply chain management supports a variety of short-term planning decisions, such as production scheduling and inventory management. In this respect, improving short-term forecast accuracy is a way to build a more agile supply chain for manufacturing companies. Demand forecasting often relies on well-established univariate forecasting methods to extrapolate historical demand. Collaboration across the supply chain, including information sharing, is suggested in the literature to improve upon the forecast accuracy of such traditional methods. In this paper, we review empirical studies considering the use of downstream information in demand forecasting and investigate different modeling approaches and forecasting methods to incorporate such data. Where empirical findings on information sharing mainly focus on point-of-sale data in two-level supply chains, this research empirically investigates the added value of using sell-through data originating from intermediaries, next to historical demand figures, in a multi-echelon supply chain. In a case study concerning a US drug manufacturer, we evaluate different methods to incorporate this data and consider both time series methods and machine learning techniques to produce multi-step ahead weekly forecasts. The results show that the manufacturer can effectively improve its short-term forecast accuracy by integrating sell-through data into the forecasting process and provide useful insights as to the different modeling approaches used. The conclusion holds for all forecast horizons considered, though it is most pronounced for one-step ahead forecasts. Therefore, our research provides a clear incentive for manufacturers to assess the forecast accuracy that can be achieved by using sell-through data.     

Poly(vinyl ethers) as building blocks for new materials

The living cationic polymerization of vinyl ethers has been used to prepare a number of new polymers with special properties. Sequential polymerization of the hydrophilic methyl vinyl ether (MVE) and the hydrophobic octadecyl vinyl ether (ODVE) has lead to amphiphilic block-copolymers with emulsifying properties for water/decane mixtures. Poly(vinyl-ether) macromonomers were obtained by end-capping of living polymers with hydroxyethyl acrylate. Copolymerization of polyODVE-macromonomer with usual acrylates lead to highly branched hydrophobic polymers. When the end-capping was performed with bifunctionally living polymers, the corresponding “bis-macromonomers” were obtained. Copolymerization of such bis-macromonomers with styrene or butyl acrylate, leads to the formation of segmented polymer networks. In the case of polyODVE-poly(butyl acrylate), these networks showed a pronounced phase separation. Due to the crystallinity of the polyODVE domains, these materials showed shape memory properties.     

Capacitance and Structure of Electric Double Layers: Comparing Brownian Dynamics and Classical Density Functional Theory

Journal of Solution Chemistry - We present a study of the structure and differential capacitance of electric double layers of aqueous electrolytes. We consider electric double layer capacitors...     

Tribenzotriquinacene Receptors for C60 Fullerene Rotors: Towards C3 Symmetrical Chiral Stators for Unidirectionally Operating Nanoratchets

The synthesis of a stereochemically pure concave tribenzotriquinacene receptor ( 7 ) for C₆₀ fullerene, possessing C₃ point group symmetry, by threefold condensation of C₂‐symmetric 1,2‐diketone synthons ( 5 ) and a hexaaminotribenzotriquinacene core ( 6 ) is described. The chiral diketone was synthesized in a five‐step reaction sequence starting from C_2h‐symmetric 2,6‐di‐tert‐butylanthracene. The highly diastereo‐discriminating Diels–Alder reaction of 2,6‐di‐tert‐butylanthracene with fumaric acid di(?)menthyl ester, catalyzed by aluminium chloride, is the relevant stereochemistry introducing step. The structure of the fullerene receptor was verified by ¹H and ¹³C NMR spectroscopy, mass spectrometry and single crystal X‐ray diffraction. VCD and ECD spectra were recorded, which were corroborated by ab initio DFT calculations, establishing the chiral nature of 7 with about 99.7 % ee, based on the ee (99.9 %) of the chiral synthon ( 1 ). The absolute configuration of 7 could thus be established as all‐S [(2S,7S,16S,21S,30S,35S)‐( 7 )]. Spectroscopic titration experiments reveal that the host forms 1:1 complexes with either pure fullerene (C₆₀) or fullerene derivatives, such as rotor 1′‐(4‐nitrophenyl)‐3′‐(4‐N,N‐dimethylaminophenyl)‐pyrazolino[4′,5′:1,2][60]fullerene ( R ). The complex stability constants of the complexes dissolved in CHCl₃/CS₂ (1:1 vol. %) are K([ C₆₀ ? 7 ])=319(±156) M ^?1 and K([ R ? 7 ])=110(±50) M ^?1. With molecular dynamics simulations using a first‐principles parameterized force field the asymmetry of the rotational potential for [ R ? 7 ] was shown, demonstrating the potential suitability of receptor 7 to act as a stator in a unidirectionally operating nanoratchet.     

Improper or classical hydrogen bonding? A comparative cryosolutions infrared study of the complexes of HCClF(2), HCCl(2)F,and HCCl(3) with dimethyl ether

Complexes of haloforms of the type HCCl(n)F(3-)(n) (n = 1-3) with dimethyl ether have been studied in liquid argon and liquid krypton, using infrared spectroscopy. For the haloform C[bond]H stretching mode, the complexation causes blue shifts of 10.6 and 4.8 cm(-1) for HCClF(2) and HCCl(2)F, respectively, while for HCCl(3) a red shift of 8.3 cm(-1) is observed. The ratio of the band areas of the haloform C[bond]H stretching in complex and monomer was determined to be 0.86(4) for HCClF(2), 33(3) for HCCl(2)F, and 56(3) for HCCl(3). These observations, combined with those for the HCF(3) complex with the same ether (J. Am. Chem. Soc. 2001, 123, 12290), have been analyzed using ab initio calculations at the MP2[double bond]FC/6-31G(d) level, and using some recent models for improper hydrogen bonding. Ab initio calculations on the haloforms embedded in a homogeneous electric field to model the influence of the ether suggest that the complexation shift of the haloform C[bond]H stretching is largely explained by the electric field effect induced by the electron donor in the proton donor. The model calculations also show that the electric field effect accounts for the observed intensity changes of the haloform C[bond]H stretches.