10,821 research outputs found
Magnetic behavior of a spin-1 Blume-Emery-Griffiths model
I study the one-dimensional spin-1 Blume-Emery-Griffiths model with bilinear
and biquadratic exchange interactions and single-ion crystal field under an
applied magnetic field. This model can be exactly mapped into a tight-binding
Hubbard model - extended to include intersite interactions - provided one
renormalizes the chemical and the on-site potentials, which become temperature
dependent. After this transformation, I provide the exact solution of the
Blume-Emery-Griffiths model in one dimension by means of the Green's functions
and equations of motion formalism. I investigate the magnetic variations of
physical quantities - such as magnetization, quadrupolar moment, susceptibility
- for different values of the interaction parameters and of the applied field,
focusing on the role played by the biquadratic interaction in the breakdown of
the magnetization plateaus.Comment: 4 pages, 5 figures. ICM 2009 (Karlsruhe) Conference proceeding
An overview of advancements in helicopter transmission design
Development of a high temperature operating helicopter gearbox is discussed
Towards feedback control of entanglement
We provide a model to investigate feedback control of entanglement. It
consists of two distant (two-level) atoms which interact through a radiation
field and becomes entangled. We then show the possibility to stabilize such
entanglement against atomic decay by means of a feedback action.Comment: 6 pages, 4 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 Ã… 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
Equations of motion approach to the spin-1/2 Ising model on the Bethe lattice
We exactly solve the ferromagnetic spin-1/2 Ising model on the Bethe lattice
in the presence of an external magnetic field by means of the equations of
motion method within the Green's function formalism. In particular, such an
approach is applied to an isomorphic model of localized Fermi particles
interacting via an intersite Coulomb interaction. A complete set of
eigenoperators is found together with the corresponding eigenvalues. The
Green's functions and the correlation functions are written in terms of a
finite set of parameters to be self-consistently determined. A procedure is
developed, that allows us to exactly fix the unknown parameters in the case of
a Bethe lattice with any coordination number z. Non-local correlation functions
up to four points are also provided together with a study of the relevant
thermodynamic quantities.Comment: RevTex, 29 pages, 13 figure
High-order correlation effects in the two-dimensional Hubbard model
The electronic states of the two-dimensional Hubbard model are investigated
by means of a 4-pole approximation within the Composite Operator Method. In
addition to the conventional Hubbard operators, we consider other two operators
which come from the hierarchy of the equations of motion and carry information
regarding nearest-neighbor spin and charge configurations. By means of this
operatorial basis, we can study the physics related to the energy scale of
J=4t^2/U in addition to the one of U. Present results show relevant physical
features, well beyond those previously obtained by means of a 2-pole
approximation, such as a four-band structure with shadow bands and a
quasi-particle peak at the Fermi level. The Fermi level stays pinned to the
band flatness located at (pi,0)-point within a wide range of hole-doping (0 <=
delta <= 0.15). A comprehensive analysis of double occupancy, internal energy,
specific heat and entropy features have been also performed. All reported
results are in excellent agreement with the data of numerical simulations.Comment: 13 pages, 8 figure
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 tomography for Dirac spinors
We present a tomographic scheme, based on spacetime symmetries, for the
reconstruction of the internal degrees of freedom of a Dirac spinor. We discuss
the circumstances under which the tomographic group can be taken as SU(2), and
how this crucially depends on the choice of the gamma matrix representation. A
tomographic reconstruction process based on discrete rotations is considered,
as well as a continuous alternative.Comment: 9 pages, LaTeX; v2: minor changes, references added. A slightly
revised version has been accepted for publication in Phys. Lett.
Purification, crystallization and preliminary X-ray analysis of a fusion of the LIM domains of LMO2 and the LID domain of Ldb1
LMO2 (LIM domain only 2), also known as rhombotin-2, is a transcriptional regulator that is essential for normal haematopoietic development. In malignant haematopoiesis, its ectopic expression in T cells is involved in the pathogenesis of leukaemia. LMO2 contains four zinc-finger domains and binds to the ubiquitous nuclear adaptor protein Ldb1 via the LIM-interaction domain (LID). Together, they act as scaffolding proteins and bridge important haematopoietic transcription factors such as SCL/Tal1, E2A and GATA-1. Solving the structure of the LMO2:Ldb1-LID complex would therefore be a first step towards understanding how haematopoietic specific protein complexes form and would also provide an attractive target for drug development in anticancer therapy, especially for T-cell leukaemia. Here, the expression, purification, crystallization and data collection of a fusion protein consisting of the two LIM domains of LMO2 linked to the LID domain of Ldb1 via a flexible linker is reported. The crystals belonged to space group C2, with unit-cell parameters a = 179.9, b = 51.5, c = 114.7 Å, β = 90.1°, and contained five molecules in the asymmetric unit. Multiple-wavelength anomalous dispersion (MAD) data have been collected at the zinc X-ray absorption edge to a resolution of 2.8 Å and the data were used to solve the structure of the LMO2:Ldb1-LID complex. Refinement and analysis of the electron-density map is in progress
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