100 research outputs found
Nonlocal Excitations and 1/8 Singularity in Cuprates
Momentum-dependent excitation spectra of the two-dimensional Hubbard model on
the square lattice have been investigated at zero temperature on the basis of
the full self-consistent projection operator method in order to clarify
nonlocal effects of electron correlations on the spectra. It is found that
intersite antiferromagnetic correlations cause shadow bands and enhance the
Mott-Hubbard splittings near the half-filling. Furthermore nonlocal excitations
are shown to move the critical doping concentration , at
which the singular quasiparticle peak is located just on the Fermi level, from
(the single-site value) to .
The latter suggests the occurance of an instability such as the stripe at
.Comment: 4 pages, 5 figures; to be published in the Journal of Korean Physical
Society (ICM12
Correlation effects in MgO and CaO: Cohesive energies and lattice constants
A recently proposed computational scheme based on local increments has been
applied to the calculation of correlation contributions to the cohesive energy
of the CaO crystal. Using ab-initio quantum chemical methods for evaluating
individual increments, we obtain 80% of the difference between the experimental
and Hartree-Fock cohesive energies. Lattice constants corrected for correlation
effects deviate by less than 1% from experimental values, in the case of MgO
and CaO.Comment: LaTeX, 4 figure
The registry of the German Network for Systemic Scleroderma: frequency of disease subsets and patterns of organ involvement
Objective. Systemic sclerosis (SSc) is a rare, heterogeneous disease, which affects different organs and therefore requires interdisciplinary diagnostic and therapeutic management. To improve the detection and follow-up of patients presenting with different disease manifestations, an interdisciplinary registry was founded with contributions from different subspecialties involved in the care of patients with SSc
Density Functional Study of the Ground and Excited State Potential Energy Surfaces of a Light-Driven Rotary Molecular Motor (3 R
Spin Symmetry Requirements in Density Functional Theory: The Proper Way to Predict Magnetic Coupling Constants in Molecules and Solids
Welches Implantat an welcher Position? Eine biomechanische Untersuchung an der distalen Fibula
Biomechanical analysis of polyaxial locking vs. non-locking plate fixation of unstable fractures of the distal fibula: A cadaver study with a bone only modelâ
Halogen Bond Asymmetry in Solution
Halogen bonding is the noncovalent interaction of halogen atoms in which they act as electron acceptors. Whereas three-center hydrogen bond complexes, [D center dot center dot center dot H center dot center dot center dot D](+) where D is an electron donor, exist in solution as rapidly equilibrating asymmetric species, the analogous halogen bonds, [D center dot center dot center dot X center dot center dot center dot D](+), have been observed so far only to adopt static and symmetric geometries. Herein, we investigate whether halogen bond asymmetry, i.e., a [D-X center dot center dot center dot D](+) bond geometry, in which one of the D-X bonds is shorter and stronger, could be induced by modulation of electronic or steric factors. We have also attempted to convert a static three-center halogen bond complex into a mixture of rapidly exchanging asymmetric isomers, [D center dot center dot center dot X-D](+) (sic) [D-X center dot center dot center dot D](+), corresponding to the preferred form of the analogous hydrogen bonded complexes. Using N-15 NMR, IPE NMR, and DFT, we prove that a static, asymmetric geometry, [D-X center dot center dot center dot D](+), is obtained upon desymmetrization of the electron density of a complex. We demonstrate computationally that conversion into a dynamic mixture of asymmetric geometries, [D center dot center dot center dot X-D](+) (sic) [D-X center dot center dot center dot D](+), is achievable upon increasing the donor-donor distance. However, due to the high energetic gain upon formation of the three-center-four electron halogen bond, the assessed complex strongly prefers to form a dimer with two static and symmetric three-center halogen bonds over a dynamic and asymmetric halogen bonded form. Our observations indicate a vastly different preference in the secondary bonding of H+ and X+. Understanding the consequences of electronic and steric influences on the strength and geometry of the three-center halogen bond provides useful knowledge on chemical bonding and for the development of improved halonium transfer agents
X-ray fluorescence analysis of metal distributions in cryogenic biological samples using large-acceptance-angle SDD detection and continuous scanning at the Hard X-ray Micro/Nano-Probe beamline P06 at PETRA III
A new Rococoâ
2 X-ray fluorescence detector was implemented into the cryogenic sample environment at the Hard X-ray Micro/Nano-Probe beamline P06 at PETRAâ
III, DESY, Hamburg, Germany. A four sensor-field cloverleaf design is optimized for the investigation of planar samples and operates in a backscattering geometry resulting in a large solid angle of up to 1.1â
steradian. The detector, coupled with the Xspressâ
3 pulse processor, enables measurements at high count rates of up to 106â
counts per second per sensor. The measured energy resolution of âŒ129â
eV (Mn Kα at 10000â
countsâ
sâ1) is only minimally impaired at the highest count rates. The resulting high detection sensitivity allows for an accurate determination of trace element distributions such as in thin frozen hydrated biological specimens. First proof-of-principle measurements using continuous-movement 2D scans of frozen hydrated HeLa cells as a model system are reported to demonstrate the potential of the new detection system
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