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排序方式: 共有208条查询结果,搜索用时 625 毫秒
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Heterometallic molecular chromium wheels are fascinating new magnetic materials. We reexamine the available experimental susceptibility data on MCr7 wheels in terms of a simple isotropic Heisenberg Hamiltonian for M=Fe, Ni, Cu, and Zn and find in that FeCr7 needs to be described with an iron–chromium exchange that is different from all other cases. In a second step we model the behavior of the proton spin lattice relaxation rate as a function of applied magnetic field for low temperatures as it is measured in nuclear magnetic resonance (NMR) experiments. It appears that CuCr7 and NiCr7 show an unexpectedly reduced relaxation rate at certain level crossings. 相似文献
3.
R. E. Ansorge B. ?sman C. N. Booth L. Burow P. Carlson R. S. De Wolf B. Eckart G. Ekspong C. Fuglesang J. Gaudaen C. Geich-Gimbel B. Holl R. Hospes K. Jon-And D. P. Johnson F. Lotse N. Manthos D. J. Munday J. E. V. Ovens W. Pelzer J. G. Rushbrooke F. Triantis L. Van hamme C. Walck C. P. Ward D. R. Ward C. J. S. Webber T. O. White G. Wilquet N. Yamdagni UA Collaboration 《Zeitschrift fur Physik C Particles and Fields》1988,41(2):179-190
A detailed analysis ofK s 0 production in \(\bar pp\) |<2.5 the average transverse momentum is found to be 0.53±0.07 GeV/c at 200 GeV and 0.62±0.08 GeV/c at 900 GeV, which is an increase with respect to data at c.m. energies below 60 GeV. TheK s 0 production cross sections in inelastic collisions are 29±4 mb at 200 GeV and 63±6 mb at 900 GeV, showing an increase compared to lower energy data. The central kaon density is found to increase as a logarithmic function of energy. At 900 GeV, where statistics are sufficient to allow one to draw conclusions, the average transverse momentum is higher in events with large charged multiplicity than in events with low multiplicity. 相似文献
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G. Eckart 《Zeitschrift für Physik A Hadrons and Nuclei》1976,33(4):145-154
The structure of the nucleon generalized optical potential (GOP) is investigated in the framework of Green's function (GF) theory. First an exact relation between its imaginary part and the total reaction cross section is derived. In the second part the GOP is decomposed using a kind of projection formalism which enables to couple in the continuum in successive steps. This is achieved by splitting up the one particle GF into a discrete and a continuous part and by summing up all contributions to the GOP containing a given numbern0 continuum propagators. Three expressions are extracted corresponding to different processes involving the scattering of at most two particles in the continuum in intermediate states. The remaining terms are argued to be small. Further support for retaining only the above three terms is given by evaluating the diagonal element of their imaginary part between the exact eigenstates of the GOP. This is shown to be approximately proportional to the sum of the total inelastic, charge exchange, pick-up and knockout cross sections. The corresponding matrix element of the exact potential is proportional to the total reaction cross section. 相似文献
6.
Alice Merca Jürgen Schnack Joris van Slageren Thorsten Glaser Hartmut Bögge Veronika Hoeke Mechtild Läge Achim Müller Bernt Krebs 《Journal of Cluster Science》2013,24(4):979-988
The gadolinium (Gd) member of a new type of heteropolytungstates that contain one lanthanide and two transition metal ions in a triangular arrangement is reported. The compound NaK6Gd0.33 [((VO)2Gd(H2O)4K2(H2O)2(Na)(H2O)2)(α-B-AsW9O33)2]·24H2O (1) was prepared from acidified aqueous solutions of Na2WO4·2H2O, As2O3 and VOSO4·5H2O to which Gd3+ ions were added. The single crystal X-ray structure analysis (monoclinic, space group P21/m) shows that the anion consists of two [α-B-AsIIIW9O33]9? trilacunary Keggin-type units linked by two VO2+, one Gd3+ as well as weakly by two K+ and one Na+ ions, resulting in a sandwich-type structure with idealized C 2v symmetry. The problem of positioning crystal lattice and special polyoxometalate sites with different cations is discussed also in connection with supramolecular chemistry aspects and as an option for further research. A fit of the magnetic susceptibility yielded exchange coupling constants of J VV = ?2.55 cm?1 (anti-ferromagnetic) between the vanadium ions and J GdV = 0.6 cm?1 (ferromagnetic) between the Gd and each of the two vanadium ions. The complete magnetochemical analysis also revealed a partial occupancy of the Na+ sites in the counter-cation–water system by Gd3+ ions (0.33 Gd3+ ions in total). 相似文献
7.
Combining Complementary Ligands into one Framework for the Construction of a Ferromagnetically Coupled [MnIII12] Wheel 下载免费PDF全文
Dr. Sergio Sanz Jamie M. Frost Thayalan Rajeshkumar Dr. Scott J. Dalgarno Dr. Gopalan Rajaraman Dr. Wolfgang Wernsdorfer Prof. Jürgen Schnack Dr. Paul. J. Lusby Prof. Euan K. Brechin 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(11):3010-3013
Phenolic oxime and diethanolamine moieties have been combined into one organic framework, resulting in the formation of a novel ligand type that can be employed to construct a rare and unusual dodecametallic Mn wheel, within which nearest neighbours are coupled ferromagnetically. 相似文献
8.
Natalie Hell Peter Beiersdorfer Gregory V. Brown Megan E. Eckart Richard L. Kelley Caroline A. Kilbourne Maurice A. Leutenegger Thomas E. Lockard F. Scott Porter Jörn Wilms 《X射线光谱测定》2020,49(1):218-233
X-ray astronomy and ground-based atomic physics have a long history of fruitful collaboration: Sound understanding of the underlying atomic physics is the key to reliable interpretation of the spectra from celestial sources; conversely, astronomical spectra have been used to benchmark and advance atomic physics. This interplay is about to become even more important as we enter a new era of high-resolution X-ray astrophysics with large effective collection area. Although high-resolution observations with the gratings on the Chandra and XMM-Newton observatories continue to drive new science, upcoming planned and proposed missions will open up new discovery space in the near future that is currently challenging to access: high-resolution spectroscopy on extended sources, in the Fe K band, and on short time scales. This review summarizes open questions in these areas and the design parameters for the Hitomi, XRISM, Athena, and Arcus observatories. The expected high quality of spectra taken with these observatories puts new constraints on the accuracy of atomic reference data required to take full advantage of the diagnostic potential of these spectra. 相似文献
9.
We show that the Chern character of a variation of polarized Hodge structures of weight one with nilpotent residues at dies up to torsion in the Chow ring, except in codimension 0. 相似文献
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