961 research outputs found
Unusual features of pomoviral RNA movement
This work is partially supported by the Scottish Government’s Rural and Environment Science and Analytical Services (RESAS) DivisionPotato mop-top pomovirus (PMTV) is one of a few viruses that can move systemically in plants in the absence of the capsid protein (CP). Pomoviruses encode the triple gene block genetic module of movement proteins (TGB 1, 2, and 3) and recent research suggests that PMTV RNA is transported either as ribonucleoprotein (RNP) complexes containing TGB1 or encapsidated in virions containing TGB1. Furthermore, there are different requirements for local or systemic (long-distance) movement. Research suggests that nucleolar passage of TGB1 may be important for the long-distance movement of both RNP and virions. Moreover, and uniquely, the long-distance movement of the CP-encoding RNA requires expression of both major and minor CP subunits and is inhibited when only the major CP sub unit is expressed. This paper reviews pomovirus research and presents a current model for RNA movement.Publisher PDFPeer reviewe
Análise da estrutura fatorial dos Testes de Torrance em estudantes portugueses
In order to verify the factorial structures of the Torrance verbal and figural tests, two activities of each instrument were applied with 193 students from the 10th and 12th years of education in Portugal. We tried to demonstrate that the collinearity of the fluency and flexibility variables could create methodological artifacts that hinder the understanding of the internal structure underlying the test. The principal component analysis without control of collinearity indicated a solution composed of four basic factors that separeted activities. Controlling for collinearity, we found a new solution, which also contained four factors that, unlike the previous result, grouped variables with similar processes but of different activities. The verbal and figural content is also an important element in the factor structure. This new arrangement makes more sense with the theory that underlies the instruments separating the different processes and content which are being measured by the activities.Com a finalidade de verificar a estrutura fatorial dos testes de Torrance, duas atividades verbais e duas figurais foram aplicadas em 193
estudantes do 10º e 12º ano do ensino secundário de Portugal. Tentou-se demonstrar que a colinearidade das variáveis fluência e flexibilidade
podem criar artefatos metodológicos que dificultam o entendimento da estrutura interna subjacente ao teste. A análise fatorial dos
componentes principais, sem controle da colinearidade, indicou uma solução composta por quatro fatores que separam basicamente as
atividades. Controlando-se a colinearidade, encontrou-se uma nova solução, também composta por quatro fatores, que, diferentemente
da anterior, organizou variáveis com processos semelhantes, mas de diferentes atividades. O tipo de conteúdo, verbal e figural, mostrou-se
ainda um importante elemento na organização dos fatores. Esse novo arranjo fez mais sentido diante da teoria que embasa os instrumentos,
ao separar os diferentes processos e conteúdos por eles avaliados
Nature of the insulating phases in the half-filled ionic Hubbard model
We investigate the ground-state phase diagram of the one-dimensional "ionic"
Hubbard model with an alternating periodic potential at half-filling by
numerical diagonalization of finite systems with the Lanczos and density matrix
renormalization group (DMRG) methods. We identify an insulator-insulator phase
transition from a band to a correlated insulator with simultaneous charge and
bond-charge order. The transition point is characterized by the vanishing of
the optical excitation gap while simultaneously the charge and spin gaps remain
finite and equal. Indications for a possible second transition into a
Mott-insulator phase are discussed.Comment: final for
Motion of Bound Domain Walls in a Spin Ladder
The elementary excitation spectrum of the spin-
antiferromagnetic (AFM) Heisenberg chain is described in terms of a pair of
freely propagating spinons. In the case of the Ising-like Heisenberg
Hamiltonian spinons can be interpreted as domain walls (DWs) separating
degenerate ground states. In dimension , the issue of spinons as
elementary excitations is still unsettled. In this paper, we study two
spin- AFM ladder models in which the individual chains are
described by the Ising-like Heisenberg Hamiltonian. The rung exchange
interactions are assumed to be pure Ising-type in one case and Ising-like
Heisenberg in the other. Using the low-energy effective Hamiltonian approach in
a perturbative formulation, we show that the spinons are coupled in bound
pairs. In the first model, the bound pairs are delocalized due to a four-spin
ring exchange term in the effective Hamiltonian. The appropriate dynamic
structure factor is calculated and the associated lineshape is found to be
almost symmetric in contrast to the 1d case. In the case of the second model,
the bound pair of spinons lowers its kinetic energy by propagating between
chains. The results obtained are consistent with recent theoretical studies and
experimental observations on ladder-like materials.Comment: 12 pages, 7 figure
Excitation Spectrum of One-dimensional Extended Ionic Hubbard Model
We use Perturbative Continuous Unitary Transformations (PCUT) to study the
one dimensional Extended Ionic Hubbard Model (EIHM) at half-filling in the band
insulator region. The extended ionic Hubbard model, in addition to the usual
ionic Hubbard model, includes an inter-site nearest-neighbor (n.n.) repulsion,
. We consider the ionic potential as unperturbed part of the Hamiltonian,
while the hopping and interaction (quartic) terms are treated as perturbation.
We calculate total energy and ionicity in the ground state. Above the ground
state, (i) we calculate the single particle excitation spectrum by adding an
electron or a hole to the system. (ii) the coherence-length and spectrum of
electron-hole excitation are obtained. Our calculations reveal that for V=0,
there are two triplet bound state modes and three singlet modes, two anti-bound
states and one bound state, while for finite values of there are four
excitonic bound states corresponding to two singlet and two triplet modes. The
major role of on-site Coulomb repulsion is to split singlet and triplet
collective excitation branches, while tends to pull the singlet branches
below the continuum to make them bound states.Comment: 10 eps figure
Effective three-band model for double perovskites
We start from a six-band model describing the transition-metal t2g orbitals
of half-metallic double perovskite systems, such as Sr2FeMoO6, in which only
one of the transition metal ions (Fe) contains important intratomic repulsion
Ufe. By eliminating the Mo orbitals using a low-energy reduction similar to
that used in the cuprates, we construct a Hamiltonian which contains only
effective t2g Fe orbitals. This allows to treat exactly Ufe, and most of the
Fe-Mo hopping. As an application, we treat the effective Hamiltonian in the
slave-boson mean-field approximation and calculate the position of the
metal-insulator transition and other quantities as a function of pressure or
on-site energy difference.Comment: 8 pages, 3 figure
The future problem solving program international: an intervention to promote creative skills in portuguese adolescents
The Future Problem Solving Program International (FPSPI) is an internationally applied educational
program that involves young people. Its theoretical foundation is both the Creative Problem Solving
Model and the Futurist Thinking. It aims to promote creative and critical thinking through a futurist
approach to problems. This study intended to analyze the effects of the program on creative skills evaluated
by the Torrance Tests of Creative Thinking (Figural Version). The participants’ perceptions of the
efficacy of the program were also assessed. This intervention was carried out with 131 adolescents over
a period of 7 months in an extra-curricular context. The evaluation of the program takes into account
periods both before and after interventions, using similar experimental and control groups. The results
showed significant statistical differences for the all skills studied and very positive perceptions of the
efficacy of FPSPI. Two significant gender differences in creative performance were also found. The
results are described and discussed in order to promote awareness for future research concerning this program(undefined)info:eu-repo/semantics/publishedVersio
Spin-orbit coupling in interacting quasi-one-dimensional electron systems
We present a new model for the study of spin-orbit coupling in interacting
quasi-one-dimensional systems and solve it exactly to find the spectral
properties of such systems. We show that the combination of spin-orbit coupling
and electron-electron interactions results in: the replacement of separate spin
and charge excitations with two new kinds of bosonic mixed-spin-charge
excitation, and a characteristic modification of the spectral function and
single-particle density of states. Our results show how manipulation of the
spin-orbit coupling, with external electric fields, can be used for the
experimental determination of microscopic interaction parameters in quantum
wires.Comment: 5 pages including 4 figures; RevTeX; to appear in Phys.Rev.Let
Spin and charge ordering in self-doped Mott insulators
We have investigated possible spin and charge ordered states in 3d
transition-metal oxides with small or negative charge-transfer energy, which
can be regarded as self-doped Mott insulators, using Hartree-Fock calculations
on d-p-type lattice models. It was found that an antiferromagnetic state with
charge ordering in oxygen 2p orbitals is favored for relatively large
charge-transfer energy and may be relevant for PrNiO and NdNiO. On the
other hand, an antiferromagnetic state with charge ordering in transition-metal
3 orbitals tends to be stable for highly negative charge-transfer energy and
can be stabilized by the breathing-type lattice distortion; this is probably
realized in YNiO.Comment: 4 pages, 4 figure
Thermopower in the strongly overdoped region of single-layer Bi2Sr2CuO6+d superconductor
The evolution of the thermoelectric power S(T) with doping, p, of
single-layer Bi2Sr2CuO6+d ceramics in the strongly overdoped region is studied
in detail. Analysis in term of drag and diffusion contributions indicates a
departure of the diffusion from the T-linear metallic behavior. This effect is
increased in the strongly overdoped range (p~0.2-0.28) and should reflect the
proximity of some topological change.Comment: 4 pages, 4 figure
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