9,678 research outputs found
Quantum anisotropic Heisenberg chains with superlattice structure: a DMRG study
Using the density matrix renormalization group technique, we study spin
superlattices composed of a repeated pattern of two spin-1/2 XXZ chains with
different anisotropy parameters. The magnetization curve can exhibit two
plateaus, a non trivial plateau with the magnetization value given by the
relative sizes of the sub-chains and another trivial plateau with zero
magnetization. We find good agreement of the value and the width of the
plateaus with the analytical results obtained previously. In the gapless
regions away from the plateaus, we compare the finite-size spin gap with the
predictions based on bosonization and find reasonable agreement. These results
confirm the validity of the Tomonaga-Luttinger liquid superlattice description
of these systems.Comment: 6 pages, 6 figure
Addressing culture in the EFL classroom: A dialogic proposal built up through dialogism
Language teaching has gone from a linguistic centered approach towards a lingocultural experience in which learning a language goes hand in hand with the understanding of, not only the target culture but the learner’s own culture. This paper intends to describe and reflect upon a collaborative and dialogical experience carried out between two teachers of the Languages Program of Universidad de la Salle. The bilateral enrichment of such a pedagogical experience not only helped the teachers to improve their language teaching contexts but also prompted the construction of a theoretical proposal to enhance intercultural awareness and develop critical intercultural competence in FL learners
Further evidence for linearly-dispersive Cooper pairs
A recent Bose-Einstein condensation (BEC) model of several cuprate
superconductors is based on bosonic Cooper pairs (CPs) moving in 3D with a
quadratic energy-momentum (dispersion) relation. The 3D BEC condensate-fraction
vs. temperature (T/Tc, where Tc is the BEC transition temperature) formula
poorly fits penetration-depth data for two cuprates in the range (1/2, 1]. We
show how these fits are dramatically improved assuming cuprates to be quasi-2D,
and how equally good fits obtain for conventional 3D and quasi-1D nanotube
superconducting data, provided the correct CP dispersion is assumed in BEC at
their assumed corresponding dimensionalities. This is offered as additional
concrete empirical evidence for linearly-dispersive pairs in another recent BEC
scenario of superconductors within which a BCS condensate turns out to be a
very special case.Comment: 9 pages, 1 figur
CP violating anomalous top-quark couplings at the LHC
We study the T odd correlations induced by CP violating anomalous top-quark
couplings at both production and decay level in the process gg --> t t_bar -->
(b mu+ nu_mu) (b_bar mu- nu_mu_bar). We consider several counting asymmetries
at the parton level and find the ones with the most sensitivity to each of
these anomalous couplings at the LHC.Comment: 14 LaTeX Pages, 1 EPS Figure, minor typos correcte
Neighborhood and community interactions determine the spatial pattern of tropical tree seedling survival
Factors affecting survival and recruitment of 3531 individually mapped seedlings of Myristicaceae were examined over three years in a highly diverse neotropical rain forest, at spatial scales of 1–9 m and 25 ha. We found convincing evidence of a community compensatory trend (CCT) in seedling survival (i.e., more abundant species had higher seedling mortality at the 25-ha scale), which suggests that density-dependent mortality may contribute to the spatial dynamics of seedling recruitment. Unlike previous studies, we demonstrate that the CCT was not caused by differences in microhabitat preferences or life history strategy among the study species. In local neighborhood analyses, the spatial autocorrelation of seedling survival was important at small spatial scales (1–5 m) but decayed rapidly with increasing distance. Relative seedling height had the greatest effect on seedling survival. Conspecific seedling density had a more negative effect on survival than heterospecific seedling density and was stronger and extended farther in rare species than in common species. Taken together, the CCT and neighborhood analyses suggest that seedling mortality is coupled more strongly to the landscape-scale abundance of conspecific large trees in common species and the local density of conspecific seedlings in rare species. We conclude that negative density dependence could promote species coexistence in this rain forest community but that the scale dependence of interactions differs between rare and common species
Transition from a phase-segregated state to single-phase incommensurate sodium ordering in Na_xCoO_2 with x \approx 0.53
Synchrotron X-ray diffraction investigations of two single crystals of
Na_xCoO_2 from different batches with composition x = 0.525-0.530 reveal
homogeneous incommensurate sodium ordering with propagation vector (0.53 0.53
0) at room-temperature. The incommensurate (qq0) superstructure exists between
220 K and 430 K. The value of q varies between q = 0.514 and 0.529, showing a
broad plateau at the latter value between 260 K and 360 K. On cooling, unusual
reversible phase segregation into two volume fractions is observed. Below 220
K, one volume fraction shows the well-known commensurate orthorhombic x = 0.50
superstructure, while a second volume fraction with x = 0.55 exhibits another
commensurate superstructure, presumably with a 6a x 6a x c hexagonal supercell.
We argue that the commensurate-to-incommensurate transition is an intrinsic
feature of samples with Na concentrations x = 0.5 + d with d ~ 0.03.Comment: Corrected/improved versio
Spin-dependent beating patterns in thermoelectric properties: Filtering the carriers of the heat flux in a Kondo adatom system
We theoretically investigate the thermoelectric properties of a
spin-polarized two-dimensional electron gas hosting a Kondo adatom hybridized
with an STM tip. Such a setup is treated within the single-impurity Anderson
model in combination with the atomic approach for the Green's functions. Due to
the spin dependence of the Fermi wavenumbers the electrical and thermal
conductances, together with thermopower and Lorenz number reveal beating
patterns as function of the STM tip position in the Kondo regime. In
particular, by tuning the lateral displacement of the tip with respect to the
adatom vicinity, the temperature and the position of the adatom level, one can
change the sign of the Seebeck coefficient through charge and spin. This opens
a possibility of the microscopic control of the heat flux analogously to that
established for the electrical current
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