1,336 research outputs found
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
D3-D7 Holographic dual of a perturbed 3D CFT
An appropriately oriented D3-D7-brane system is the holographic dual of
relativistic Fermions occupying a 2+1-dimensional defect embedded in
3+1-dimensional spacetime. The Fermions interact via fields of
Yang-Mills theory in the 3+1-dimensional bulk. Recently, using internal flux to
stabilize the system in the probe limit, a number of solutions which
are dual to conformal field theories with Fermion content have been found. We
use holographic techniques to study perturbations of a particular one of the
conformal field theories by relevant operators. Generally, the response of a
conformal field theory to such a perturbation grows and becomes nonperturbative
at low energy scales. We shall find that a perturbation which switches on a
background magnetic field and Fermion mass induces a renormalization
group flow that can be studied perturbatively in the limit of small . We
solve the leading order explicitly. We find that, for one particular value of
internal flux, the system exhibits magnetic catalysis, the spontaneous breaking
of chiral symmetry enhanced by the presence of the magnetic field. In the
process, we derive formulae predicting the Debye screening length of the
Fermion-antiFermion plasma at finite density and the diamagnetic moment of the
ground state of the Fermion system in the presence of a magnetic field.Comment: 23 pages, two figures; typos corrected, some comments adde
A Study of Effective Factors on the Behavioural Characteristics of Clayey Sands
As in recent years liquefaction phenomena have occurred in sandy soils containing different amounts of clay contents, it was concluded that in addition to silty sands, clayey sands are also vulnerable to liquefaction phenomenon. So, the urge for comprehensive study aroused to cover the issue. In this paper, the effect of clay content and its plasticity properties on behavioural characteristics of clayey sands under various density and confining pressure values have been investigated. To achieve the goal, about a hundred monotonic triaxial tests were performed on remoulded specimens of sandy soils containing different clay contents with different plasticity values. Based on the results, the latter factors affect peak strength, steady state strength, undrain brittleness and residual shear strength, considerably. Furthermore, great results obtained on the issue of whether clay content or plasticity properties variations is much effective
A numerical scheme for a class of nonlinear Fredholm integral equations of the second kind
AbstractIn this paper an iterative approach for obtaining approximate solutions for a class of nonlinear Fredholm integral equations of the second kind is proposed. The approach contains two steps: at the first one, we define a discretized form of the integral equation and prove that by considering some conditions on the kernel of the integral equation, solution of the discretized form converges to the exact solution of the problem. Following that, in the next step, solution of the discretized form is approximated by an iterative approach. We finally on some examples show the efficiency of the proposed approach
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
Individual Optimization of the Insertion of a Preformed Cochlear Implant Electrode Array
Purpose. The aim of this study was to show that individual adjustment of the curling behaviour of a preformed cochlear implant (CI) electrode array to the patient-specific shape of the cochlea can improve the insertion process in terms of reduced risk of insertion trauma. Methods. Geometry and curling behaviour of preformed, commercially available electrode arrays were modelled. Additionally, the anatomy of each small, medium-sized, and large human cochlea was modelled to consider anatomical variations. Finally, using a custom-made simulation tool, three different insertion strategies (conventional Advanced Off-Stylet (AOS) insertion technique, an automated implementation of the AOS technique, and a manually optimized insertion process) were simulated and compared with respect to the risk of insertion-related trauma. The risk of trauma was evaluated using a newly developed “trauma risk” rating scale. Results. Using this simulation-based approach, it was shown that an individually optimized insertion procedure is advantageous compared with the AOS insertion technique. Conclusion. This finding leads to the conclusion that, in general, consideration of the specific curling behaviour of a CI electrode array is beneficial in terms of less traumatic insertion. Therefore, these results highlight an entirely novel aspect of clinical application of preformed perimodiolar electrode arrays in general
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