101 research outputs found
Assessment of vertical facial and dentoalveolar changes using panoramic radiography
The purpose of the study was to analyse longitudinal vertical facial and dentoalveolar changes using panoramic radiographs (PRs) and to compare the results with measurements on lateral cephalometric radiographs (LCRs) in order to determine whether, under certain circumstances, the radiation dose for a patient may be reduced by taking only a PR instead of a PR and a LCR. Pre- and post-treatment PRs and LCRs of 30 (15 females and 15 males) orthodontically treated adolescents (mean age pre-treatment 10.9 years, post-treatment 13.4 years) were analysed using Pearson's correlation coefficients and gender differences using Fisher's z-transformation. The results revealed that most variables exhibited larger absolute values on PRs than on LCRs. Comparison of dentoskeletal morphology between the LCRs and the PRs revealed moderate to high, mostly statistically significant, interrelations both before and after orthodontic treatment. The lowest correlations were found for the maxillary jaw base angle (NL/H; r= 0.35***) and the highest for the gonial angle (ML/RL; r = 0.90***). However, when assessing the combined growth and treatment changes from before to after treatment, only weak to moderate, not statistically significant, interrelations were found between LCRs and PRs. Anterior face height (AFH; r = 0.43***), the mandibular plane angle (ML/H; r = 0.06*), and the distance of the incisal tip of the most extruded mandibular incisor to the ML-line (ii-ML; r = −0.21*) were the only statistically significant parameters. The average group differences for growth and treatment changes, however, were small for most parameters. Analysis of vertical facial and dentoalveolar parameters on PRs delivers a moderate approximation to the situation depicted on LCRs. However, PRs cannot be recommended for the analysis of individual longitudinal changes in vertical facial and dentoalveolar parameter
Bose-Glass Phases in Disordered Quantum Magnets
In disordered spin systems with antiferromagnetic Heisenberg exchange,
transitions into and out of a magnetic-field-induced ordered phase pass through
a unique regime. Using quantum Monte Carlo simulations to study the
zero-temperature behavior, these intermediate regions are determined to be a
Bose-Glass phase. The localization of field-induced triplons causes a finite
compressibility and hence glassiness in the disordered phase.Comment: 4 pages, 4 figure
Magnetic Bose glass phases of coupled antiferromagnetic dimers with site dilution
We numerically investigate the phase diagram of two-dimensional site-diluted
coupled dimer systems in an external magnetic field. We show that this phase
diagram is characterized by the presence of an extended Bose glass, not
accessible to mean-field approximation, and stemming from the localization of
two distinct species of bosonic quasiparticles appearing in the ground state.
On the one hand, non-magnetic impurities doped into the dimer-singlet phase of
a weakly coupled dimer system are known to free up local magnetic moments. The
deviations of these local moments from full polarization along the field can be
mapped onto a gas of bosonic quasiparticles, which undergo condensation in zero
and very weak magnetic fields, corresponding to transverse long-range
antiferromagnetic order. An increasing magnetic field lowers the density of
such quasiparticles to a critical value at which a quantum phase transition
occurs, corresponding to the quasiparticle localization on clusters of local
magnets (dimers, trimers, etc.) and to the onset of a Bose glass. Strong
finite-size quantum fluctuations hinder further depletion of quasiparticles
from such clusters, and thus lead to the appearance of pseudo-plateaus in the
magnetization curve of the system. On the other hand, site dilution hinders the
field-induced Bose-Einstein condensation of triplet quasiparticles on the
intact dimers, and it introduces instead a Bose glass of triplets. A thorough
numerical investigation of the phase diagram for a planar system of coupled
dimers shows that the two above-mentioned Bose glass phases are continuously
connected, and they overlap in a finite region of parameter space, thus
featuring a two-species Bose glass. The quantum phase transition from Bose
glass to magnetic order in two dimensions is marked by novel universal
exponents.Comment: 15 pages, 16 figure
Uncertain Data Envelopment Analysis
Data Envelopment Analysis (DEA) is a nonparametric, data driven method to conduct relative performance measurements among a set of decision making units (DMUs). Efficiency scores are computed based on assessing input and output data for each DMU by means of linear programming. Traditionally, these data are assumed to be known precisely. We instead consider the situation in which data is uncertain, and in this case, we demonstrate that efficiency scores increase monotonically with uncertainty. This enables inefficient DMUs to leverage uncertainty to counter their assessment of being inefficient. Using the framework of robust optimization, we propose an uncertain DEA (uDEA) model for which an optimal solution determines 1) the maximum possible efficiency score of a DMU over all permissible uncertainties, and 2) the minimal amount of uncertainty that is required to achieve this efficiency score. We show that the uDEA model is a proper generalization of traditional DEA and provide a first-order algorithm to solve the uDEA model with ellipsoidal uncertainty sets. Finally, we present a case study applying uDEA to the problem of deciding efficiency of radiotherapy treatments
A possible scenario for the mechanism of high-Tc superconductivity based on experimental data
The issue of the mechanism of high-Tc superconductivity remains open. In this
contribution, we propose a new scenario for the mechanism of superconductivity
in cuprates based on analysis of experimental data, mainly tunneling, neutron
scattering and muon-spin-relaxation data, made earlier (see e.g. Mod. Phys.
Lett. B 19 (2005) 743). A specific feature of this scenario is the mechanism of
the establishment of long-range phase coherence among Cooper pairs, based on
recent experimental data obtained in nonsuperconducting materials.Comment: 2 pages with 2 figures (Dresden conference
Adaptive design of nano-scale dielectric structures for photonics
Using adaptive algorithms, the design of nano-scale dielectric structures for
photonic applications is explored. Widths of dielectric layers in a linear
array are adjusted to match target responses of optical transmission as a
function of energy. Two complementary approaches are discussed. The first
approach uses adaptive local random updates and progressively adjusts
individual dielectric layer widths. The second approach is based on global
updating functions in which large subgroups of layers are adjusted
simultaneously. Both schemes are applied to obtain specific target responses of
the transmission function within selected energy windows, such as discontinuous
cut-off or power-law decay filters close to a photonic band edge. These
adaptive algorithms are found to be effective tools in the custom design of
nano-scale photonic dielectric structures.Comment: 4 pages Revtex, 4 embedded EPS figure
Quantum Phase Transitions in Coupled Dimer Compounds
We study the critical properties in cubic systems of antiferromagnetically
coupled spin dimers near magnetic-field induced quantum phase transitions. The
quantum critical points in the zero-temperature phase diagrams are determined
from quantum Monte Carlo simulations. Furthermore, scaling properties of the
uniform magnetization and the staggered transverse magnetization across the
quantum phase transition in magnetic fields are calculated. The critical
exponents are derived from Ginzburg-Landau theory. We find excellent agreement
between the quantum Monte Carlo simulations and the analytical results.Comment: 7 pages, 9 eps-figure
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