10,729 research outputs found
Frustration-driven QPT in the 1D extended anisotropic Heisenberg model
By using Density Matrix Renormalization Group (DMRG) technique we study the
1D extended anisotropic Heisenberg model. We find that starting from the
ferromagnetic phase, the system undergoes two quantum phase transitions (QPTs)
induced by frustration. By increasing the next-nearest-neighbor (NNN)
interaction, the ground state of the system changes smoothly from a completely
polarized state to a NNN correlated one. On the contrary, letting the in-plane
interaction to be greater than the out-of-plane one, the ground state changes
abruptly.Comment: 4 pages, 4 figures, to be presented at CSMAG-07 Kosice, Slovakia,
July 200
Exact solution of the 1D Hubbard model in the atomic limit with inter-site magnetic coupling
In this paper we present for the first time the exact solution in the
narrow-band limit of the 1D extended Hubbard model with nearest-neighbour
spin-spin interactions described by an exchange constant J. An external
magnetic field h is also taken into account. This result has been obtained in
the framework of the Green's functions formalism, using the Composite Operator
Method. By means of this theoretical background, we have studied some relevant
features such as double occupancy, magnetization, spin-spin and charge-charge
correlation functions and derived a phase diagram for both ferro (J>0) and
anti-ferro (J<0) coupling in the limit of zero temperature. We also report a
study on density of states, specific heat, charge and spin susceptibilities. In
the limit of zero temperature, we show that the model exhibits a very rich
phase diagram characterized by different magnetic orders and by the coexistence
of charge and spin orderings at commensurate filling. Moreover, our analysis at
finite temperature of density of states and response functions shows the
presence of low-temperature charge and spin excitations near the phase
boundaries.Comment: 20 pages, 32 figure
Supplanting crystallography or supplementing microscopy? A combined approach to the study of an enveloped virus
The recent advances in the resolution obtained by single-particle reconstructions from cryo-electron microscopy (cryo-EM) have led to an increase in studies that combine X-ray crystallographic results with those of electron microscopy (EM). Here, such a combination is described in the determination of the structure of an enveloped animal virus, Semliki Forest virus, at 9 Å resolution. The issues of model bias in determination of the structure, the definition of resolution in a single-particle reconstruction, the effect of the correction of the contrast-transfer function on the structure determined and the use of a high-resolution structure of a subunit in the interpretation of the structure of the complex are addressed
Advanced vehicle separation apparatus
A method of obtaining test data from two independent models or bodies in a conventional wind tunnel is described. The system makes efficient use of wind tunnel test time with computer control performing complex coordinate transformations necessary for model positioning. The apparatus is designed to be used in any of the three Unitary Wind Tunnels at NASA-Ames Research Center. Mechanical design details and a brief description of the control system for the separation apparatus are presented
Rotary mechanism for wind tunnel stall/spin studies
The critical problem of stall-spin characteristics of high performance aircraft and the need for experimental data in this area are reviewed. A rotary mechanism for obtaining this aerodynamic data in a conventional wind tunnel is presented. The intricacies of the drive systems and the articulation available through such a mechanism are described
Bosonic sector of the two-dimensional Hubbard model studied within a two-pole approximation
The charge and spin dynamics of the two-dimensional Hubbard model in the
paramagnetic phase is first studied by means of the two-pole approximation
within the framework of the Composite Operator Method. The fully
self-consistent scheme requires: no decoupling, the fulfillment of both Pauli
principle and hydrodynamics constraints, the simultaneous solution of fermionic
and bosonic sectors and a very rich momentum dependence of the response
functions. The temperature and momentum dependencies, as well as the dependency
on the Coulomb repulsion strength and the filling, of the calculated charge and
spin susceptibilities and correlation functions are in very good agreement with
the numerical calculations present in the literature
Quantum State Reconstruction of a Bose-Einstein Condensate
We propose a tomographic scheme to reconstruct the quantum state of a
Bose-Einstein condensate, exploiting the radiation field as a probe and
considering the atomic internal degrees of freedom. The density matrix in the
number state basis can be directly retrieved from the atom counting
probabilities.Comment: 11 pages, LaTeX file, no figures, to appear in Europhysics Letter
Electron-radiation interaction in a Penning trap: beyond the dipole approximation
We investigate the physics of a single trapped electron interacting with a
radiation field without the dipole approximation. This gives new physical
insights in the so-called geonium theory.Comment: 12 pages, RevTeX, 6 figures, Approved for publication in Phys. Rev.
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