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排序方式: 共有290条查询结果,搜索用时 93 毫秒
101.
Adina Jung Volkan Filiz Sofia Rangou Kristian Buhr Petra Merten Janina Hahn Juliana Clodt Clarissa Abetz Volker Abetz 《Macromolecular rapid communications》2013,34(7):610-615
The formation of integral asymmetric membranes from ABC triblock terpolymers by non‐solvent‐induced phase separation is shown. They are compared with the AB diblock copolymer precursors. Triblock terpolymers of polystyrene‐block‐poly(2‐vinylpyridine)‐block‐poly(ethylene oxide) (PS‐b‐P2VP‐b‐PEO) with two compositions are investigated. The third block supports the formation of a membrane in a case, where the corresponding diblock copolymer does not form a good membrane. In addition, the hydrophilicity is increased by the third block and due to the hydroxyl group the possibility of post‐functionalization is given. The morphologies are imaged by scanning electron microscopy. The influence of the PEO on the membrane properties is analyzed by water flux, retention, and dynamic contact angle measurements.
102.
Michael Quentin Dirk Blondin Janina Klasen Rotem Shlomo Lanzman Falk-Roland Miese Christian Arsov Peter Albers Gerald Antoch Hans-Jörg Wittsack 《Magnetic resonance imaging》2012
Purpose
To evaluate which mathematical model (monoexponential, biexponential, statistical, kurtosis) fits best to the diffusion-weighted signal in prostate magnetic resonance imaging (MRI).Materials and Methods
24 prostate 3-T MRI examinations of young volunteers (YV, n= 8), patients with biopsy proven prostate cancer (PC, n= 8) and an aged matched control group (AC, n= 8) were included. Diffusion-weighted imaging was performed using 11 b-values ranging from 0 to 800 s/mm2.Results
Monoexponential apparent diffusion coefficient (ADC) values were significantly (P<.001) lower in the peripheral (PZ) zone (1.18±0.16 mm2/s) and the central (CZ) zone (0.73±0.13 mm2/s) of YV compared to AC (PZ 1.92±0.17 mm2/s; CZ 1.35±0.21 mm2/s). In PC ADCmono values (0.61±0.06 mm2/s) were significantly (P<.001) lower than in the peripheral of central zone of AC. Using the statistical analysis (Akaike information criteria) in YV most pixels were best described by the biexponential model (82%), the statistical model, respectively kurtosis (93%) each compared to the monoexponential model. In PC the majority of pixels was best described by the monoexponential model (57%) compared to the biexponential model.Conclusion
Although a more complex model might provide a better fitting when multiple b-values are used, the monoexponential analyses for ADC calculation in prostate MRI is sufficient to discriminate prostate cancer from normal tissue using b-values ranging from 0 to 800 s/mm2. 相似文献103.
Steady-state spectroscopic studies of two ortho (-OCH3 and -OH) derivatives of methyl p-dimethylaminobenzoate have been performed. The absorption spectra of molecules under study are analyzed taking into consideration results of quantum chemical semiempirical calculations. The fluorescence spectra of these molecules possess in polar solvents two bands, i.e., the locally excited and intramolecular charge transfer (ICT) fluorescence band. Their intensity ratio as well as the fluorescence/phosphorescence intensity ratio determined at 77 K depends on the solvent polarity. Theoretical studies of the TICT phenomenon have been made in order to explain the dual emission of molecules under study. Calculated electric dipole moments of these molecules in the ground, S0, and excited, S1(LE) and S1(ICT) states, have been compared with experimentally determined data. Theoretically determined transition energies, ΔEi, oscillator strengths, fi, and electric dipole moments μS0, μS1(LE) and μS1(ICT) of the planar donor-acceptor (D/A) conformer agree with experimental data. According to Marcus theory inner- and outer-solvatation sphere reorganization energies (λout, λin) are calculated using the determined spectroscopic properties of molecules under study. 相似文献
104.
N‐alkoxypyridinium salts as coinitiators in radical polymerization: Synthesis and Photochemical Properties 下载免费PDF全文
Janina Kabatc Katarzyna Kostrzewska Robert Dobosz Łukasz Orzeł Katarzyna Jurek 《Journal of polymer science. Part A, Polymer chemistry》2017,55(17):2840-2850
A few N‐alkoxypyridinium salts are developed as photoinitiators for efficient polymerization reactions. They are characterized by absorption properties below 300 nm, and generate alkoxy radicals on UV‐Vis light exposure. The squarylium dye was used as a blue‐light photosensitizer. Polymerization results are correlated with the photochemistry of N‐alkoxypyridinium salts. The quenching of the excited singlet state of squarylium dye by pyridinium salt and the formation of the semioxidized species of squaraine suggests an electron transfer from an excited dye to a coinitiator, and that the resulting oxygen‐centered radical initiates the polymerization process. The chemical mechanism was investigated by steady state photolysis and nanosecond laser flash photolysis experiments. Photoinitiating activity of new photoinitiators for initiation of polymerization of trimethylolpropane triacrylate in the UV‐blue light region was compared with photoinitiating ability of selected commercially available initiators. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2840–2850 相似文献
105.
106.
Marian Mikokajczyk Piotr Bakczewski Krzysztof Wroblewski Janina Karolak-Wojciechowska Andrzej Miller Michał W. Wieczorek Michail Y. Antipin Yurij T. Struchkov 《Tetrahedron》1984,40(23):4885-4892
1H-NMR studies and X-ray analysis indicate that 2-dimethoxyphosphoryl-1,3,5-trithiane exists both in solution and in the crystal in a chair conformation with the dimethoxyphosphoryl group at C-2 being axial. 相似文献
107.
108.
Marek L. Główka Andrzej Ołczak Janina Kamińska 《Journal of chemical crystallography》1996,26(1):47-51
The title compound crystallizes in the orthorhombic space group P212121, withZ=4,a=6.068(1)Å,b=10.922(1)Å, andc=21.713(2)Å. The compound is the chiral ligand of a copper complex used as an enantioselective catalyst. It crystallizes from methanol in the keto-enamine form, though the enol-imine isomer predominates in the solution. Most N-salicylideneamines studied by X-ray are enol-imines. The two tautomeric forms may interchange through anintramolecular hydrogen bond and the distances between non-H atoms in the resulting cyclic –O–H...N=C–C=C- or –C=O...H–N–C=C- fragment may be misleading, so that H atom position is the crucial factor for determination of the proper tautomeric form. 相似文献
109.
Thermogravimetry was used in the study of the kinetics of dehydration of MnSO4·5H2O, CuSO4·5H2O and 3CdSO4·8H2O under static air atmosphere. The values of the kinetic and thermodynamic parameters for each stage of thermal dehydration were calculated from α(T) data by using the integral method, applying the Coats-Redfern approximation. The best model for all stages of dehydration is random nucleation model F1. The dependencies of enthalpy on entropy of activated complexes for different kinetic models were described. The linear relation was calculated between the Gibbs energy of activated complexes and the maximum dehydration rate temperature for analysed dehydration processes. 相似文献
110.
The applicability of hydrogen chemisorption in a pulse chromatographic system for determining the dispersity of -alumina supported rhenium catalysts (10.4 wt.% and 1.04 wt.%) preheated in hydrogen at 550–800 °C is shown.
, - (10,4 .% 1,04 .%), 550–800°C.相似文献