443 research outputs found
From the triangular to the kagome lattice: Following the footprints of the ordered state
We study the spin-1/2 Heisenberg model in a lattice that interpolates between
the triangular and the kagome lattices. The exchange interaction along the
bonds of the kagome lattice is J, and the one along the bonds connecting kagome
and non-kagome sites is J', so that J'=J corresponds to the triangular limit
and J'=0 to the kagome one. We use variational and exact diagonalization
techniques. We analyze the behavior of the order parameter for the
antiferromagnetic phase of the triangular lattice, the spin gap, and the
structure of the spin excitations as functions of J'/J. Our results indicate
that the antiferromagnetic order is not affected by the reduction of J' down to
J'/J ~ 0.2. Below this value, antiferromagnetic correlations grow weaker, a
description of the ground state in terms of a Neel phase renormalized by
quantum fluctuations becomes inadequate, and the finite-size spectra develop
features that are not compatible with antiferromagnetic ordering. However, this
phase does not appear to be connected to the kagome phase as well, as the
low-energy spectra do not evolve with continuity for J'-> 0 to the kagome
limit. In particular, for any non-zero value of J', the latter interaction sets
the energy scale for the low-lying spin excitations, and a gapless triplet
spectrum, destabilizing the kagome phase, is expected.Comment: 9 pages, 10 Figures. To be published in PR
Detecting Change in the Urban Road Environment Along a Route Based on Traffic Sign and Crossroad Data
Occurrences of traffic signs that belong to certain sign categories and occurrences of crossroads of various topologies are utilized in detecting change in the urban road environment that moves past an ego-car. Three urban environment types, namely downtown, residential and industrial/commercial areas, are considered in the study and changes between these are to be detected. In the preparatory phase, the ego-car is used for traffic sign and crossroads data collection. In the application phase, the ego-car hosts an advanced driver assistance system (ADAS) that captures and analyzes images of the road environment and computes the required input data to the proposed road environment detection (RoED) subsystem. A statistical inference method relying on the minimum description length (MDL) principle was applied to the change detection problem at hand. The above occurrences along a route are seen as a realization of an inhomogeneous marked Poisson process. Page-Hinkley change detectors tuned to empirical data were set to work to detect change in the urban road environment. The process and the quality of the change detection are demonstrated via examples from three urban settlements in Hungary.
Document type: Part of book or chapter of boo
Two-dimensional array of magnetic particles: The role of an interaction cutoff
Based on theoretical results and simulations, in two-dimensional arrangements
of a dense dipolar particle system, there are two relevant local dipole
arrangements: (1) a ferromagnetic state with dipoles organized in a triangular
lattice, and (2) an anti-ferromagnetic state with dipoles organized in a square
lattice. In order to accelerate simulation algorithms we search for the
possibility of cutting off the interaction potential. Simulations on a dipolar
two-line system lead to the observation that the ferromagnetic state is much
more sensitive to the interaction cutoff than the corresponding
anti-ferromagnetic state. For (measured in particle diameters)
there is no substantial change in the energetical balance of the ferromagnetic
and anti-ferromagnetic state and the ferromagnetic state slightly dominates
over the anti-ferromagnetic state, while the situation is changed rapidly for
lower interaction cutoff values, leading to the disappearance of the
ferromagnetic ground state. We studied the effect of bending ferromagnetic and
anti-ferromagnetic two-line systems and we observed that the cutoff has a major
impact on the energetical balance of the ferromagnetic and anti-ferromagnetic
state for . Based on our results we argue that is a
reasonable choice for dipole-dipole interaction cutoff in two-dimensional
dipolar hard sphere systems, if one is interested in local ordering.Comment: 8 page
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Bulk electronic structure of superconducting LaRu2P2 single crystals measured by soft x-ray angle-resolved photoemission spectroscopy
We present a soft X-ray angle-resolved photoemission spectroscopy (SX-ARPES)
study of the stoichiometric pnictide superconductor LaRu2P2. The observed
electronic structure is in good agreement with density functional theory (DFT)
calculations. However, it is significantly different from its counterpart in
high-temperature superconducting Fe-pnictides. In particular the bandwidth
renormalization present in the Fe-pnictides (~2 - 3) is negligible in LaRu2P2
even though the mass enhancement is similar in both systems. Our results
suggest that the superconductivity in LaRu2P2 has a different origin with
respect to the iron pnictides. Finally we demonstrate that the increased
probing depth of SX-ARPES, compared to the widely used ultraviolet ARPES, is
essential in determining the bulk electronic structure in the experiment.Comment: 4 pages, 4 figures, 1 supplemental material. Accepted for publication
in Physical Review Letter
Nonmagnetic Insulating States near the Mott Transitions on Lattices with Geometrical Frustration and Implications for -(ET)Cu
We study phase diagrams of the Hubbard model on anisotropic triangular
lattices, which also represents a model for -type BEDT-TTF compounds.
In contrast with mean-field predictions, path-integral renormalization group
calculations show a universal presence of nonmagnetic insulator sandwitched by
antiferromagnetic insulator and paramagnetic metals. The nonmagnetic phase does
not show a simple translational symmetry breakings such as flux phases,
implying a genuine Mott insulator. We discuss possible relevance on the
nonmagnetic insulating phase found in -(ET)Cu.Comment: 4pages including 7 figure
Surface Modification of Titanium Dental Implants by Excimer Laser
The perfect osseointegration process of the dental implants depends among other factors on the surfact characteristics of the titanium. In this study enlarged mechanical roughness was produced by a laser-based technique, in order to decrease the healing period of the implant. There are different ways of forming laser induced surface
structures. In the case of mask projection techniques the surface can be modified in larger areas and surface patterns. An ArF nanosecond excimer laser was used in the experiments because of the advantageous properties of the excimer beams. Effective polishing by homogeneous laser illumination in the 3-5 J/cm2 fluence range was performed as confirmed by SEM and AFM studies. Holes of about
20 mm diameter and 10 mm in depth, with high aspect ratio and protrusions around the edges were ablated into the titanium surface with subsequent pulses of ns ArF excimer laser. To avoid easily breakable protrusions we applied excimer pulse durations of 0.5 picoseconds. In this case we obtained melting- and ridge-free ablation of titanium. The laser treatment influenced the chemical composition of the surface in two respects. On the one hand it
removed carbonaceous contamination as indicated by XPS and XRD measurements, demonstrating that cleaning of the surface does not alter the original crystalline structure. On the other hand, XPS measurements proved that pulsed laser oxidation in air increased the thickness of the surface oxide layer, promoting better osseointegration
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