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排序方式: 共有329条查询结果,搜索用时 265 毫秒
221.
222.
I.H Dunbar 《Annals of Physics》1982,138(1):53-77
The weak production of leptons in high energy proton-antiproton collisions is investigated using the parton model. Charged and neutral current signals are calculated both with the standard SU(2) × U(1) gauge model and with a pointlike four-fermion coupling. In addition to differential cross-sections, angular and polarization asymmetries are calculated and their significance is assessed. 相似文献
223.
224.
We study the relaxation limit for the Aw-Rascle system of traffic flow. For this we apply the theory of invariant regions and the compensated compactness method to get global existence of Cauchy problem for a particular Aw-Rascle system with source, where the source is the relaxation term, and we show the convergence of this solutions to the equilibrium state. 相似文献
225.
Miyasaka H Izawa T Takahashi N Yamashita M Dunbar KR 《Journal of the American Chemical Society》2006,128(35):11358-11359
Two isostructural 2D assemblies composed of [Ru2(O2CCF3)4] and TCNQ or TCNQF4 in a 2:1 ratio were synthesized: [{Ru2(O2CCF3)4}2TCNQ].3(p-xylene) (1b) and [{Ru2(O2CCF3)4}2TCNQF4].3(p-xylene) (2). In 1b, the TCNQ moiety is assigned to be neutral because of no significant electron transfer from the Ru24+ units. Therefore, the magnetic property of 1b can be understood to be a paramagnetic nature of the isolated Ru24+ unit, while, a fully charge-transfer from the Ru2 units to the TCNQF4 molecules in 2 leads to charge delocalization spreading over the 2D network and allows a long-range magnetic order to occur. On the basis of an idea of the resonance scheme in charge-transfer D2A network systems, the first successful example of a charge-transferred magnet in the Ru2-TCNQ system was rationally designed by tuning redox between [Ru2]4+ and the TCNQ molecule changing from TCNQ to TCNQF4. 相似文献
226.
Nazario Lopez Andrey V. Prosvirin Dr. Hanhua Zhao Dr. Wolfgang Wernsdorfer Dr. Kim R. Dunbar Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(42):11390-11400
A series of isostructural compounds with formula [M(TCNQF4)2(H2O)6]TCNQF4 ? 3 H2O (M=Tb ( 1 ), Y ( 2 ), Y:Tb (74:26) ( 3 ), and Y:Tb (97:3) ( 4 ); TCNQF4= tetrafluorotetracyanoquinodimethane) were prepared and their magnetic properties investigated. Compounds 1 , 3 , and 4 show the beginning of a frequency‐dependent out‐of‐phase ac signal, and decreasing intensity of the signal with decreased concentration of TbIII ions in the diluted samples is observed. No out‐of‐phase signal was observed for 2 , an indication that the behavior of 1 , 3 , and 4 is indicative of slow paramagnetic relaxation of TbIII ions in the samples. A more detailed micro‐SQUID study at low temperature revealed an interplay between single‐molecule magnetic (SMM) behavior and a phonon bottleneck (PB) effect, and that these properties depend on the concentration of diamagnetic yttrium ions. A combination of SMM and PB phenomena was found for 1 , whereby the PB effect increases with increasing dilution until eventually a pure PB effect is observed for 2 . The PB behavior is interpreted as being due to the presence of a “sea of organic S=1/2 radicals” from the TCNQF4 radicals in these compounds. The present data underscore the fact that the presence of an out‐of‐phase ac signal may not, in fact, be caused by SMM behavior, particularly when magnetic metal ions are combined with organic radical ligands such as those found in the organocyanide family. 相似文献
227.
Coherent Dynamics of Direct-Current-Driven Quantum-Dot-Array with Two Time-Dependent Embedded Impurities 下载免费PDF全文
The coherent dynamics of dc-driven quantum-dot array with two embedded time-dependent impurities is investigated, the exact crossings and avoided crossings in the quasienergies are associated with the evolution dynamics of the electron by the introduction of the envelope lines of the site's maximum returning probability. Through a perturbative scheme, the time-dependent Hamiltonian is replaced by an equivalent static one, whose structure reveals the new quantum tunnelling mechanism in the time-periodic driving system and sheds light on the alternative interpretation of dynamic localization and delocalization. 相似文献
228.
Eric W. Reinheimer Marc Fourmigué Kim R. Dunbar 《Journal of chemical crystallography》2009,39(10):723-729
Abstract The synthesis and crystal structure of the salt (BPDT-TTF)2[W6O19] is described. The compound crystallizes in the triclinic space group P − 1 with a = 10.927(2) ?, b = 11.904(2) ?, c = 12.660(2) ?, α = 101.261(5)°, β = 115.174(5)°, and γ = 114.434(5)°. The bond length of the central C=C bond in BPDT-TTF is 1.384(17) ?, in accord with an oxidation state of +1
for the BPDT-TTF radical-cations and the observed stoichiometry between BPDT-TTF and [W6O19]2− which is 2:1.
Index Abstract The X-ray crystallographic structure of the radical cation salt (BPDT-TTF)2[W6O19] has been determined and its structural features, including examples of interatomic interactions, as well as its synthetic
preparation are discussed.
相似文献
229.
230.
Kyle L. Dunbar Maria Dell Evelyn M. Molloy Florian Kloss Christian Hertweck 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(37):13148-13152
Thioamide‐containing nonribosomal peptides (NRPs) are exceedingly rare. Recently the biosynthetic gene cluster for the thioamidated NRP antibiotic closthioamide (CTA) was reported, however, the enzyme responsible for and the timing of thioamide formation remained enigmatic. Here, genome editing, biochemical assays, and mutational studies are used to demonstrate that an Fe‐S cluster containing member of the adenine nucleotide α‐hydrolase protein superfamily (CtaC) is responsible for sulfur incorporation during CTA biosynthesis. However, unlike all previously characterized members, CtaC functions in a thiotemplated manner. In addition to prompting a revision of the CTA biosynthetic pathway, the reconstitution of CtaC provides the first example of a NRP thioamide synthetase. Finally, CtaC is used as a bioinformatic handle to demonstrate that thioamidated NRP biosynthetic gene clusters are more widespread than previously appreciated. 相似文献