95 research outputs found
Differential Form of the Skornyakov--Ter-Martirosyan Equations
The Skornyakov--Ter-Martirosyan three-boson integral equations in momentum
space are transformed into differential equations. This allows us to take into
account quite directly the Danilov condition providing self-adjointness of the
underlying three-body Hamiltonian with zero-range pair interactions. For the
helium trimer the numerical solutions of the resulting differential equations
are compared with those of the Faddeev-type AGS equations.Comment: 4 pages, 2 figure
Benchmark calculations for elastic fermion-dimer scattering
We present continuum and lattice calculations for elastic scattering between
a fermion and a bound dimer in the shallow binding limit. For the continuum
calculation we use the Skorniakov-Ter-Martirosian (STM) integral equation to
determine the scattering length and effective range parameter to high
precision. For the lattice calculation we use the finite-volume method of
L\"uscher. We take into account topological finite-volume corrections to the
dimer binding energy which depend on the momentum of the dimer. After
subtracting these effects, we find from the lattice calculation kappa a_fd =
1.174(9) and kappa r_fd = -0.029(13). These results agree well with the
continuum values kappa a_fd = 1.17907(1) and kappa r_fd = -0.0383(3) obtained
from the STM equation. We discuss applications to cold atomic Fermi gases,
deuteron-neutron scattering in the spin-quartet channel, and lattice
calculations of scattering for nuclei and hadronic molecules at finite volume.Comment: 16 pages, 5 figure
Underthreshold resonances in three-particle molecular systems
To determine the lifetimes of Efimov states of negative two-atomic ions, the
problem of resonance scattering of a light particle on a pair of identical
particles has been considered. An analytic expression has been obtained for
resonance widths in the limit of forces of zero radius and low binding energies
in pairs. Calculations are compared with the numerical solution of the Faddeev
integral equations in a wide region of masses of the light particle. It is
shown that the widths of underthreshold resonances in the scattering amplitude
obtained from the integral equations with the Yamaguchi potential are well
described by the analytic expression, which allows this expression to be used
in the mass region inaccessible for numerical calculations. It has been
concluded that the lifetime of highly excited negative molecular ions with a
binding energy close to the threshold of disintegration is practically
unlimited.Comment: Latex, 15 page
Correlation effects in Ni 3d states of LaNiPO
The electronic structure of the new superconducting material LaNiPO
experimentally probed by soft X-ray spectroscopy and theoretically calculated
by the combination of local density approximation with Dynamical Mean-Field
Theory (LDA+DMFT) are compared herein. We have measured the Ni L2,3 X-ray
emission (XES) and absorption (XAS) spectra which probe the occupied and
unoccupied the Ni 3d states, respectively. In LaNiPO, the Ni 3d states are
strongly renormalized by dynamical correlations and shifted about 1.5 eV lower
in the valence band than the corresponding Fe 3d states in LaFeAsO. We further
obtain a lower Hubbard band at -9 eV below the Fermi level in LaNiPO which
bears striking resemblance to the lower Hubbard band in the correlated oxide
NiO, while no such band is observed in LaFeAsO. These results are also
supported by the intensity ratio between the transition metal L2 and L3 bands
measured experimentally to be higher in LaNiPO than in LaFeAsO, indicating the
presence of the stronger electron correlations in the Ni 3d states in LaNiPO in
comparison with the Fe 3d states in LaFeAsO. These findings are in accordance
with resonantly excited transition metal L3 X-ray emission spectra which probe
occupied metal 3d-states and show the appearance of the lower Hubbard band in
LaNiPO and NiO and its absence in LaFeAsO.Comment: 6 pages, 5 figure
Scattering length for helium atom-diatom collision
We present results on the scattering lengths of ^4He--^4He_2 and ^3He--^4He_2
collisions. We also study the consequence of varying the coupling constant of
the atom-atom interaction.Comment: Contribution to Proceedings of the International Workshop ``Critical
Stability of Few-Body Quantum Systems'' (Dresden, October 17--22, 2005
Construction and Solution of a Wannier-Functions Based Hamiltonian in the Pseudopotential Plane-Wave Framework for Strongly Correlated Materials
Ab initio determination of model Hamiltonian parameters for strongly correlated materials is a key issue in applying many-particle theoretical tools to real narrow-band materials. We propose a selfcontained calculation scheme to construct, with an ab initio approach, and solve such a Hamiltonian. The scheme uses a Wannier-function-basis set, with the Coulomb interaction parameter U obtained specifically for theseWannier functions via constrained Density functional theory (DFT) calculations. The Hamiltonian is solved by Dynamical Mean-Field Theory (DMFT) with the effective impurity problem treated by the Quantum Monte Carlo (QMC) method. Our scheme is based on the pseudopotential plane-wave method, which makes it suitable for developments addressing the challenging problem of crystal structural relaxations and transformations due to correlation effects. We have applied our scheme to the "charge transfer insulator" material nickel oxide and demonstrate a good agreement with the experimental photoemission spectra. © 2008 Springer.This work was supported by the Russian Foundation for Basic Research under the grant RFFI 07-02-00041. We are grateful to Jan Kunes and Dieter Vollhardt for helpful discussions and for supplying the QMC-DMFT computer code. We also acknowledge support for this work by the Light Source Theory Network, LighTnet, of the EU
Microwave-Assisted synthesis and evaluation of antibacterial activity of novel 6-fluoroaryl-[1,2,4]triazolo[1,5-A]pyrimidines
A series of 6-fluoroaryl substituted [1,2,4]triazolo[1,5-A]pyrimidines have been synthesized by using the microwave-Assisted Suzuki cross-coupling reaction from readily available 6-bromo-[1,2,4]triazolo[1,5-A]pyrimidine. The antimicrobial activity of new compounds has been evaluated in vitro against Mycobacterium tuberculosis H37Rv and gram-negative (Neisseria gonorrhoeae ATCC 49226) bacteria. © ARKAT-USA, Inc
Synthesis, X-ray crystal structure and antimycobacterial activity of enantiomerically pure 1-ethyl-2,3-dicyano-5-(het)aryl-6-hetaryl-1,6- dihydropyrazines
The Petasis reaction of 6-alkoxy adducts of 1-alkyl-2,3-dicyano-5- arylpyrazinium salts with aromatic boronic acids, such as 2-thienylboronic, 2-furanylboronic and 3-thienylboronic acids, or their benzo analogs in dichloromethane proceeds smoothly at room temperature with the formation of the corresponding 5-aryl-6-hetaryl substituted 1,6-dihydropyrazine derivatives. All dihydropyrazines were separated as pure enantiomers by chiral HPLC, and their absolute configurations for each pair of enantiomers have been determined by X-ray analysis. Individual enantiomers were screened in vitro for their antimycobacterial activities against Mycobacterium tuberculosis H37Rv, avium, terrae and extensively drug-resistant and multi-drug-resistant strains isolated from tuberculosis patients in Ural region (Russia). It has been shown that several compounds exhibit a good level of antituberculosis activity compared to the reference drugs. © ARKAT-USA, Inc
Electronic structure and possible pseudogap behavior in iron based superconductors
Starting from the simplified analytic model of electronic spectrum of iron -
pnictogen (chalcogen) high - temperature superconductors close to the Fermi
level, we discuss the influence of antiferromagneting (AFM)scattering both for
stoichiometric case and the region of possible short - range order AFM
fluctuations in doped compounds. Qualitative picture of the evolution of
electronic spectrum and Fermi surfaces (FS) for different dopings is presented,
with the aim of comparison with existing and future ARPES experiments. Both
electron and hole dopings are considered and possible pseudogap behavior
connected with partial FS "destruction" is demonstrated, explaining some recent
experiments.Comment: 5 pages, 4 figures, published versio
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