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81.
Lucas Ueberricke Dr. Bahiru Punja Benke Tobias Kirschbaum Dr. Sebastian Hahn Dr. Frank Rominger Prof. Dr. Uwe H. F. Bunz Prof. Dr. Michael Mastalerz 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(6):2043-2049
A six-step synthesis towards a tribenzotriquinacene (TBTQ) bearing three quinoxalinophenanthrophenazine (QPP) units is presented. The optoelectronic properties are investigated and the effect of the three-dimensional arrangement of the individual QPP planes is examined using optical spectroscopy, electrochemical analysis and quantum-chemical calculations. 相似文献
82.
Influence of higher harmonics of the undulator in X‐ray polarimetry and crystal monochromator design
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Berit Marx‐Glowna Kai S. Schulze Ingo Uschmann Tino Kämpfer Günter Weber Christoph Hahn Hans‐Christian Wille Kai Schlage Ralf Röhlsberger Eckhart Förster Thomas Stöhlker Gerhard G. Paulus 《Journal of synchrotron radiation》2015,22(5):1151-1154
The spectrum of the undulator radiation of beamline P01 at Petra III has been measured after passing a multiple reflection channel‐cut polarimeter. Odd and even harmonics up to the 15th order, as well as Compton peaks which were produced by the high harmonics in the spectrum, could been measured. These additional contributions can have a tremendous influence on the performance of the polarimeter and have to be taken into account for further polarimeter designs. 相似文献
83.
Yang Li Yuan‐Yuan An Jian‐Zhong Fan Xiao‐Xu Liu Xin Li F. Ekkehardt Hahn Yao‐Yu Wang Ying‐Feng Han 《Angewandte Chemie (International ed. in English)》2020,59(25):10073-10080
A series of supramolecular assemblies of types [Ag8( L )4](PF6)8 and [Ag4( L )2](PF6)4, obtained from the tetraphenylethylene (TPE) bridged tetrakis(1,2,4‐triazolium) salts H4‐L(PF6)4 and AgI ions, is described. The assembly type obtained dependends on the N‐wingtip substituents of H4‐L(PF6)4. Changes in the lengths of the N4‐wingtip substituents enables controlled formation of assemblies with either [Ag4( L )2](PF6)4 or [Ag8( L )4](PF6)8 stoichiometry. The molecular structures of selected [Ag8( L )4](PF6)8 and [Ag4( L )2](PF6)4 assemblies were determined by X‐ray diffraction analyses. While H4‐ L (PF6)4 does not exhibit fluorescence in solution, their tetra‐NHC (NHC=N‐heterocyclic carbene) assemblies do upon NHC–metal coordination. Upon irradiation, all assemblies undergo a light‐induced, supramolecule‐to‐supramolecule structural transformation by an oxidative photocyclization involving phenyl groups of the TPE core, resulting in a significant change of the luminescence properties. 相似文献
84.
David M. Koshy Shucheng Chen Dong Un Lee Michaela Burke Stevens Ahmed M. Abdellah Samuel M. Dull Gan Chen Dennis Nordlund Alessandro Gallo Christopher Hahn Drew C. Higgins Zhenan Bao Thomas F. Jaramillo 《Angewandte Chemie (International ed. in English)》2020,59(10):4043-4050
Ni,N‐doped carbon catalysts have shown promising catalytic performance for CO2 electroreduction (CO2R) to CO; this activity has often been attributed to the presence of nitrogen‐coordinated, single Ni atom active sites. However, experimentally confirming Ni?N bonding and correlating CO2 reduction (CO2R) activity to these species has remained a fundamental challenge. We synthesized polyacrylonitrile‐derived Ni,N‐doped carbon electrocatalysts (Ni‐PACN) with a range of pyrolysis temperatures and Ni loadings and correlated their electrochemical activity with extensive physiochemical characterization to rigorously address the origin of activity in these materials. We found that the CO2R to CO partial current density increased with increased Ni content before plateauing at 2 wt % which suggests a dispersed Ni active site. These dispersed active sites were investigated by hard and soft X‐ray spectroscopy, which revealed that pyrrolic nitrogen ligands selectively bind Ni atoms in a distorted square‐planar geometry that strongly resembles the active sites of molecular metal–porphyrin catalysts. 相似文献
85.
Ralph Weissleder David D. Stark Guillermo Elizondo Peter F. Hahn Carolyn Compton Sanjay Saini Jack Wittenberg Joseph T. Ferrucci 《Magnetic resonance imaging》1988,6(6):675-681
Thirteen patients with biopsy proven hepatic lymphoma (2 Hodgkin, 11 Non-Hodgkin) and a control group of 15 patients with hepatic metastases were analyzed quantitatively and qualitatively by MRI. Focal hepatic lymphoma was most reliably detected (eight of eight patients) and appeared hypointense relative to liver on T1 weighted (CNR − 7.4 ± 2.3) and hyperintense on T2 weighted (CNR + 8.4 ± 2.9) images. The mean T1 and T2 relaxation times of focal hepatic lymphoma (T1 = 832 ± 234 msec, T2 = 84 ± 16 ms) differed significantly from adjacent non-tumorous liver (T1 = 420 ± 121 ms, T2 = 51 ± 9 ms; p < 0.05), however CNR values and relaxation times were similar to those of hepatic metastases. Diffuse hepatic lymphoma (microscopic periportal infiltration) was undetectable by MRI in three patients by either morphologic features or quantitative criteria. A mixed pattern of hepatic lymphoma (focal lesions and diffuse infiltration) showed focal areas of slightly decreased signal intensity on T1 weighted images (CNR = −1.7 ± 0.4) while T2 weighted images revealed multiple regions of focal hyperintensity (CNR = +13.3 ± 8.4) superimposed on a diffusely hyperintense liver. Our experience demonstrates that either T1 or T2 weighted techniques are useful in detecting focal and that T2 weighted techniques are useful in detecting mixed hepatic lymphoma. Conventional image derived relaxation time measurements and quantitative parameters were of no additional diagnostic value. 相似文献
86.
87.
2-Iminothiazole, an isoform of 2-aminothiazole, is a scaffold of synthetic and medicinal significance. We have reported an efficient method by which alkyl group of 2-alkyliminothiazoles is changed into other alkyl groups by isothiocyanates. In this article, a detailed mechanistic aspect, and the scopes and limitations were disclosed. All the reactions were carried out in toluene at 105 °C without any additive. The reaction is a reversible process and the equilibrium is determined by the reactivity of both reactants, in which the more electron-withdrawing alkyl or aryl groups at the 2-imino group or isothiocyanate showed higher reactivities. With this simple method, we effectively altered the alkyl group attached on the imine nitrogen. A synthetic problem in 2-iminothiazole chemistry, synthesis of amino acid-derived 2-iminothiazole was solved in a very simple manner. Using suitably designed 2-iminothiazole substrate, the electrophilic reactivity of various isothiocyanates could be empirically compared by this exchange reaction. Moreover, successful exchange reaction using isocyanates instead of isothiocyanates broadened the utility of this reaction. 相似文献
88.
A concept of variational dimension is introduced for a random sequence with stationary increments. In the Gaussian case, the variational dimension in the limit coincides with the Hausdorff dimension of a proper random process. Applications of the concept are illustrated by examples of neurological data and network traffic analysis. 相似文献
89.
Hahn FE Wittenbecher L Le Van D Fröhlich R 《Angewandte Chemie (International ed. in English)》2000,39(3):541-544
Evidence for the Wanzlick equilibrium between carbene 1 and dibenzotetraazafulvalene (1)(2) at ambient temperature has been found (see scheme). Enetetramines of type (1)(2) can also be cleaved by coordinatively unsaturated transition metal compounds to form dicarbene complexes. 相似文献
90.
Detection of myocardial viability by low-dose dobutamine Cine MR imaging 总被引:15,自引:0,他引:15
Sandstede JJ Bertsch G Beer M Kenn W Werner E Pabst T Lipke C Kretschmer S Neubauer S Hahn D 《Magnetic resonance imaging》1999,17(10):614-1443
The purpose of this work was to test the diagnostic value of dobutamine stress magnetic resonance imaging (MRI) for predicting recovery of regional myocardial contractility after revascularization. Cardiac wall motion abnormalities are due to either non-viable and/or scarred, or viable, but hibernating, myocardial tissue. Dobutamine stress leads to increased systolic wall thickening only in viable myocardium. Twenty-five patients with akinetic or dyskinetic myocardial regions were examined with a Cine FLASH-2D sequence at rest and during dobutamine stress (10 μg/kg/min). Patients were re-examined at rest 3, and in case of persisting wall motion defects, 6 months after revascularization. Criterion of viability was increasing end-systolic wall thickening during stress and/or at follow-up. Akinetic regions related either to the LAD (n = 19) or to the RCA (n = 6) were judged viable if >=50% of the affected segments improved. MR studies were completed in all subjects without arrhythmia or need for early terminations due to symptoms. Sensitivity, specificity, and positive predictive value for the prediction of myocardial viability were 61%, 90%, and 87% for the segment-related analysis, and 76%, 100%, and 100% for the patient-related analysis based on coronary artery distribution, respectively. Dobutamine stress MRI allows to predict global functional recovery of akinetic myocardial regions after revascularization with a high positive predictive value and high specificity. 相似文献