Exact ferromagnetic ground state of pentagon chains

We model conducting pentagon chains with a multi-orbital Hubbard model and prove that well below half filling, exact ferromagnetic ground states appear. The rigorous method we use is based on the transformation of original hamiltonian into positive semidefinite form. This technique is independent of the spatial dimension and does not require integrability of the model. The obtained ferromagnetism is connected to dispersionless bands but in a much broader sense than flat-band ferromagnetism requires, where on every site a Hubbard term is present. In our case, only a small percentage of, even randomly distributed, sites are only interacting.     

Effective Hamiltonian of the two-band Hubbard model: An exact result

An effective Hamiltonian for the two-band Hubbard model was derived by a canonical transformation which was calculated and summed up to infinite order . The transformed Hamiltonian contains terms with strongly renormalized interaction energies. These new interaction energies show sign reversals as a function of the hopping integral in addition to a strong reduction in the charge-transfer gap and a significant increase in the attractive oxygen Hubbard term.     

A new approach to surface photovoltage measurements on hydrogenated microcrystalline silicon layers

A new approach to the surface photovoltage method is demonstrated on thick undoped microcrystalline silicon films grown on different substrates. The model, which includes top as well as bottom space-charge regions, gives a good picture of rather complex experiments and allows good fitting of theoretical curves to experimental results. This method gives us not only the diffusion length of minority carriers but also information on the existence and properties of the space-charge regions in the sample and the results are verified by comparison with the standard procedure.     

Total spin in the density matrix renormalization group algorithm

A new density matrix renormalization group (DMRG) algorithm is presented which conserves the total spin. This is the first time that standard DMRG is extended to exploit fully the symmetries of the Hamiltonian. The obtained general procedure works for any operator, even operators that do not commute with the Hamiltonian. The new method gives substantial improvements over the standard DMRG.     

Experimental determination of trapping efficiency of optical tweezers

We report an experimental determination of trapping efficiency of optical fields acting on spherical particles diluted in viscous fluids. This parameter was derived from experimentally calculated trap stiffness for micron-sized silica beads with particle radii of 1.5 and 4.8 microns, respectively. In order to obtain the trap stiffness, we used the equipartition theorem, and introduced an experimental procedure to calibrate the optical tweezers set-up. The method consists of the calculation of the trapping efficiency by using the curves of the trap stiffness vs. the incident power. Using this approach we measured the efficiency for different values of displacements of the beads in the optical trap, and compared these results with numerical and theoretical calculations reported in the literature, and an excellent agreement was found. We have shown that the ratio of efficiencies is very close to the ratio of the particle radii.     

Variational solution of the one-dimensional t–J model

A new variational scheme based on a modified Bethe–Peierls method is used to study the ground state properties of the one-dimensional t–J model. Expectation values are evaluated by cutting out a four-site cluster from a correlated Fermi sea, the ground state of which is described by a variational trial wave function. We study a generalized Gutzwiller state where nearest-neighbour hole–hole correlations are controlled variationally. From the electron concentration dependence of the ground state energy, we determine the true thermodynamic boundary where segregation into an electron-rich, and purely hole phase sets in. We also determine the spinodal line and pair susceptibilities. The variational method is applied also to an extended t–J–V model, where V is the coupling constant of the charge interaction term.     

My Group's Fate Is My Fate: Identity-Fused Americans and Spaniards Link Personal Life Quality to Outcome of 2008 Elections

People differ in their reactions to the outcomes of their group. Whereas some may revel in victory and mourn in defeat, others may internalize victory but distance themselves from defeat. Here, we sought to relate these divergent reactions to two forms of alignment with groups–identity fusion and group identification. Investigations of the 2008 elections in the United States and Spain revealed that people who were “fused” with their political party internalized both victory and defeat, but highly identified persons internalized only victory. We discuss how these findings bear on the conceptual distinctions between identity fusion and group identification.     

Habituación a largo plazo y claves ambientales en humanos

Resumen

Con objeto de comprobar si, como el modelo de Wagner (1976, 1978) postula, durante la habituación a largo plazo se establece una asociación entre el estímulo habituador y las claves ambientales, se llevaron a cabo dos experimentos en humanos. En el experimento I el cambio de contexto ambiental produjo una rehabituación más rápida y una tendencia a una menor recuperación de la respuesta en la segunda situación (empleando un tono de 105 dbs., comienzo súbito y veinticuatro horas de intervalo entre sesiones). En el experimento II (empleando un tono de 80 dbs., comienzo gradual y cuarenta y ocho horas de intervalo entre sesiones), el cambio de contexto ambiental produjo una menor recuperatión de la respuesta y una tendencia a una mayor tasa de habituación. Las instrucciones «informativas» no produjeron habituación diferente de las «normales». Se consideran estos resultados como acordes con una interpretación atencional tradicional de la habituación más que con el modelo de Wagner.