99 research outputs found
Molecular spintronics using noncollinear magnetic molecules
We investigate the spin transport through strongly anisotropic noncollinear
magnetic molecules and find that the noncollinear magnetization acts as a
spin-switching device for the current. Moreover, spin currents are shown to
offer a viable route to selectively prepare the molecular device in one of two
degenerate noncollinear magnetic states. Spin-currents can be also used to
create a non-zero density of toroidal magnetization in a recently characterized
Dy_3 noncollinear magnet.Comment: 4 pages, 3 figures, submitted to Phys. Rev. Let
Complete spectrum of the infinite- Hubbard ring using group theory
We present a full analytical solution of the multiconfigurational
strongly-correlated mixed-valence problem corresponding to the -Hubbard ring
filled with electrons, and infinite on-site repulsion. While the
eigenvalues and the eigenstates of the model are known already, analytical
determination of their degeneracy is presented here for the first time. The
full solution, including degeneracy count, is achieved for each spin
configuration by mapping the Hubbard model into a set of Huckel-annulene
problems for rings of variable size. The number and size of these effective
Huckel annulenes, both crucial to obtain Hubbard states and their degeneracy,
are determined by solving a well-known combinatorial enumeration problem, the
necklace problem for beads and two colors, within each subgroup of the
permutation group. Symmetry-adapted solution of the necklace
enumeration problem is finally achieved by means of the subduction of coset
representation technique [S. Fujita, Theor. Chim. Acta 76, 247 (1989)], which
provides a general and elegant strategy to solve the one-hole infinite-
Hubbard problem, including degeneracy count, for any ring size. The proposed
group theoretical strategy to solve the infinite- Hubbard problem for
electrons, is easily generalized to the case of arbitrary electron count ,
by analyzing the permutation group and all its subgroups.Comment: 31 pages, 4 figures. Submitte
Lanthanide-radical magnetic coupling in [LnPc]: Competing exchange mechanisms captured via ab initio multi-reference calculations
We present a computational investigation of the intramolecular exchange
coupling in [LnPc] (Ln = Tb, Dy, Ho, and Er) between the Ln 4f
electrons and the spin-1/2 radical on the phthalocyanine ligands. A series of
ab initio multi-configurational/multi-reference Complete/Restricted Active
Space Self-Consistent-Field calculations (CASSCF/RASSCF), including
non-perturbative spin--orbit coupling, were performed on [LnPc] and on
the smaller model compound [LnPz]. We find that the exchange coupling
mechanisms are restricted by symmetry, but also dependent on the spin
polarization effect triggered by the Pc ligands -- excitations.
The calculated exchange splittings are small, amounting to at most a few
cm, in disagreement with previous literature reports of strong
antiferromagnetic coupling, but in good agreement with recent EPR experiments
on [TbPc]. Furthermore, the coupling strength is found to decrease from
[TbPc] to [ErPc], with decreasing number of unpaired electron
spins in the lanthanide ground (Hund's rule) Russell--Saunders term.Comment: 20 pages, 2 figure
Theory of NMR chemical shift in an electronic state with arbitrary degeneracy
We present a theory of nuclear magnetic resonance (NMR) shielding tensors for
electronic states with arbitrary degeneracy. The shieldings are here expressed
in terms of generalized Zeeman () and hyperfine () tensors,
of all ranks allowed by the size of degeneracy. Contrary to recent
proposals [T. O. Pennanen and J. Vaara, Phys. Rev. Lett. 100, 133002 (2008)],
our theory is valid in the strong spin-orbit coupling limit. Ab initio
calculations for the 4-fold degenerate ground state of
lanthanide-doped fluorite crystals CaF:Ln (Ln = Pr, Nd,
Sm, and Dy) show that previously neglected contributions can
account for more than 50% of the paramagnetic shift.Comment: Supporting information included; 5 pages; new figure adde
Direitos humanos e contemporaneidade no Brasil
- Divulgação dos SUMĂRIOS das obras recentemente incorporadas ao acervo da Biblioteca Ministro Oscar Saraiva do STJ. Em respeito Ă Lei de Direitos Autorais, nĂŁo disponibilizamos a obra na Ăntegra.- Localização na estante: 341.231.14(81) D598h- Organizado por: Alessandro Martins Prado, AndrĂ© Luiz da Silva e Guilherme Soncini da Costa
Catastrophic NAD+ Depletion in Activated T Lymphocytes through Nampt Inhibition Reduces Demyelination and Disability in EAE
Nicotinamide phosphoribosyltransferase (Nampt) inhibitors such as FK866 are potent inhibitors of NAD+ synthesis that show promise for the treatment of different forms of cancer. Based on Nampt upregulation in activated T lymphocytes and on preliminary reports of lymphopenia in FK866 treated patients, we have investigated FK866 for its capacity to interfere with T lymphocyte function and survival. Intracellular pyridine nucleotides, ATP, mitochondrial function, viability, proliferation, activation markers and cytokine secretion were assessed in resting and in activated human T lymphocytes. In addition, we used experimental autoimmune encephalomyelitis (EAE) as a model of T-cell mediated autoimmune disease to assess FK866 efficacy in vivo. We show that activated, but not resting, T lymphocytes undergo massive NAD+ depletion upon FK866-mediated Nampt inhibition. As a consequence, impaired proliferation, reduced IFN-γ and TNF-α production, and finally autophagic cell demise result. We demonstrate that upregulation of the NAD+-degrading enzyme poly-(ADP-ribose)-polymerase (PARP) by activated T cells enhances their susceptibility to NAD+ depletion. In addition, we relate defective IFN-γ and TNF-α production in response to FK866 to impaired Sirt6 activity. Finally, we show that FK866 strikingly reduces the neurological damage and the clinical manifestations of EAE. In conclusion, Nampt inhibitors (and possibly Sirt6 inhibitors) could be used to modulate T cell-mediated immune responses and thereby be beneficial in immune-mediated disorders
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