排序方式: 共有128条查询结果,搜索用时 30 毫秒
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Braun C Börger SL Boyko TD Miehe G Ehrenberg H Höhn P Moewes A Schnick W 《Journal of the American Chemical Society》2011,133(12):4307-4315
High-pressure synthesis allows both fundamental and materials science research to gain unprecedented insight into the inner nature of materials properties at extreme environment conditions. Here, we report on the high-pressure synthesis and characterization of γ-Ca(3)N(2) and the high-pressure behavior of Mg(3)N(2). Investigation of M(3)N(2) (M = Ca, Mg) at high-pressure has been quite challenging due to the high reactivity of these compounds. Ex situ experiments have been performed using a multianvil press at pressures from 8 to 18 GPa (1000-1200 °C). Additional in situ experiments from 0 to 6 GPa (at RT) at the multianvil press MAX 80 (HASYLAB, Beamline F.2.1, Hamburg) have been carried out. The new cubic high-pressure phase γ-Ca(3)N(2) with anti-Th(3)P(4) defect structure exhibits a significant increase in coordination numbers compared to α-Ca(3)N(2). Contrary, Mg(3)N(2) shows decomposition starting at surprisingly low pressures, thereby acting as a precursor for Mg nanoparticle formation with bcc structure. Soft X-ray spectroscopy in conjunction with first principles DFT calculations have been used to explore the electronic structure and show that γ-Ca(3)N(2) is a semiconductor with inherent nitrogen vacancies. 相似文献
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A straightforward, highly stereoselective protocol toward the synthesis of deuterium-labeled (2R,3S,4S)-β-cyclohexenylserine has been developed. Key steps are a Nozaki-Hiyama-Kishi reaction generating the stereogenic centers and a ring-closing metathesis for the construction of the cyclohexenyl ring system. The labeled amino acid was further activated as an SNAc-ester for feeding experiments. 相似文献
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Dyer HE Huijser S Schwarz AD Wang C Duchateau R Mountford P 《Dalton transactions (Cambridge, England : 2003)》2008,(1):32-35
The reaction of Sm{N(SiMe3)2}3 with the bis(phenol)amines H2O2N(R) (H2O2N(R) = RCH2CH2N(2-HO-3,5-C6H2(t)Bu2)2; R = OMe, NMe2 or Me) gave exclusively zwitterions Sm(O2N(R))(HO2N(R)). For R = OMe or NMe2 these were efficient catalysts for the ring-opening polymerisation of epsilon-caprolactone and D,L-lactide with a tendency to form cyclic esters; in contrast, no polymerisation was observed for R = Me. 相似文献
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Saskia Mioduszewski 《The European Physical Journal C - Particles and Fields》2009,61(4):741-745
Results on high-p
T
probes shown at the Hard Probes 2008 Conference are summarized, with an appreciation of the improvements in precision of
the measurements and experimental techniques since the beginning of RHIC operation. Particular attention is given to the latest
measurements of the nuclear modification factor of identified particles, photon-hadron correlation measurements, and full
jet reconstruction. 相似文献
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Biesheuvel PM Lindhoud S de Vries R Cohen Stuart MA 《Langmuir : the ACS journal of surfaces and colloids》2006,22(3):1291-1300
We study the phase behavior of mixtures of oppositely charged nanoparticles, both theoretically and experimentally. As an experimental model system we consider mixtures of lysozyme and lysozyme that has been chemically modified in such a way that its charge is nearly equal in magnitude but opposite in sign to that of unmodified lysozyme. We observe reversible macroscopic phase separation that is sensitive not only to protein concentration and ionic strength, but also to temperature. We introduce a heterogeneous Poisson-Boltzmann cell model that generally applies to mixtures of oppositely charged nanoparticles. To account for the phase behavior of our experimental model system, in addition to steric and electrostatic interactions, we need to include a temperature-dependent short-ranged interaction between the lysozyme molecules, the exact origin of which is unknown. The strength and temperature dependence of the short-ranged attraction is found to be of the same order of magnitude as that between unmodified lysozyme molecules. The presence of a rather strong short-ranged attraction in our model system precludes the formation of colloidal liquid phases (or complex coacervates) such as those typically found in mixtures of globular protein molecules and oppositely charged polyelectrolytes. 相似文献