Low-Temperature Excitations of Dilute Lattice Spin Glasses

A new approach to exploring low-temperature excitations in finite-dimensional lattice spin glasses is proposed. By focusing on bond-diluted lattices just above the percolation threshold, large system sizes $L$ can be obtained which lead to enhanced scaling regimes and more accurate exponents. Furthermore, this method in principle remains practical for any dimension, yielding exponents that so far have been elusive. This approach is demonstrated by determining the stiffness exponent for dimensions $d=3$, $d=6$ (the upper critical dimension), and $d=7$. Key is the application of an exact reduction algorithm, which eliminates a large fraction of spins, so that the reduced lattices never exceed $\sim10^3$ variables for sizes as large as L=30 in $d=3$, L=9 in $d=6$, or L=8 in $d=7$. Finite size scaling analysis gives $y_3=0.24(1)$ for $d=3$, significantly improving on previous work. The results for $d=6$ and $d=7$, $y_6=1.1(1)$ and $y_7=1.24(5)$, are entirely new and are compared with mean-field predictions made for d>=6.Comment: 7 pages, LaTex, 7 ps-figures included, added result for stiffness in d=7, as to appear in Europhysics Letters (see http://www.physics.emory.edu/faculty/boettcher/ for related information

Damage spreading in two dimensional geometrically frustrated lattices: the triangular and kagome anistropic Heisenberg model

The technique of damage spreading is used to study the phase diagram of the easy axis anisotropic Heisenberg antiferromagnet on two geometrically frustrated lattices. The triangular and kagome systems are built up from triangular units that either share edges or corners respectively. The triangular lattice undergoes two sequential Kosterlitz-Thouless transitions while the kagome lattice undergoes a glassy transition. In both cases, the phase boundaries obtained using damage spreading are in good agreement with those obtained from equilibrium Monte Carlo simulations.Comment: 7 pages, 4 figure

Deep learning to detect macular atrophy in wet age-related macular degeneration using optical coherence tomography

Here, we have developed a deep learning method to fully automatically detect and quantify six main clinically relevant atrophic features associated with macular atrophy (MA) using optical coherence tomography (OCT) analysis of patients with wet age-related macular degeneration (AMD). The development of MA in patients with AMD results in irreversible blindness, and there is currently no effective method of early diagnosis of this condition, despite the recent development of unique treatments. Using OCT dataset of a total of 2211 B-scans from 45 volumetric scans of 8 patients, a convolutional neural network using one-against-all strategy was trained to present all six atrophic features followed by a validation to evaluate the performance of the models. The model predictive performance has achieved a mean dice similarity coefficient score of 0.706 ± 0.039, a mean Precision score of 0.834 ± 0.048, and a mean Sensitivity score of 0.615 ± 0.051. These results show the unique potential of using artificially intelligence-aided methods for early detection and identification of the progression of MA in wet AMD, which can further support and assist clinical decisions

International approaches for delivery of positive newborn bloodspot screening results for CF

BACKGROUND: Newborn bloodspot screening (NBS) for cystic fibrosis (CF) is a well-established public health strategy with international standards. A European survey demonstrated considerable variability in approach to delivering a positive NBS result. We used a mixed methods approach to explore healthcare systems and beliefs around this process. METHODS: We used semi-structured interviews and online questionnaires with a purposive, international sample of health professionals involved in communicating positive NBS results to parents. Data were analysed using thematic analysis and Qualtrics Survey Software. RESULTS: In total, 63 healthcare professionals were approached; 25 interviews were conducted with delegates at the 2017 ECFS conference, 4 online questionnaires were subsequently completed by participants in the EU, 1 from Australia and 33 from the US. Methods used to communicate positive NBS results to families varied considerably. This influenced the quality and quantity of information provided which had the potential to heighten anxiety and affect timely diagnostic testing. Participants identified positive practices including systems to improve the timeliness of screening and processing of results, as well as areas for improvement. Respondents stated that knowledge of CF and familiarity with the family were both important when deciding who should communicate positive NBS results. CONCLUSIONS: Guidance and practice regarding communication of positive NBS results for CF to families varies considerably internationally. Further research is needed to ensure information received is accurate, up-to-date and from the most appropriate person. Also, that all children are followed up in a timely manner to minimise potential negative outcomes for the child and family

Micromagnetic simulations of interacting dipoles on a fcc lattice: Application to nanoparticle assemblies

Micromagnetic simulations are used to examine the effects of cubic and axial anisotropy, magnetostatic interactions and temperature on M-H loops for a collection of magnetic dipoles on fcc and sc lattices. We employ a simple model of interacting dipoles that represent single-domain particles in an attempt to explain recent experimental data on ordered arrays of magnetoferritin nanoparticles that demonstrate the crucial role of interactions between particles in a fcc lattice. Significant agreement between the simulation and experimental results is achieved, and the impact of intra-particle degrees of freedom and surface effects on thermal fluctuations are investigated.Comment: 10 pages, 9 figure

Monte Carlo Simulation of the Heisenberg Antiferromagnet on a Triangular Lattice: Topological Excitations

We have simulated the classical Heisenberg antiferromagnet on a triangular lattice using a local Monte Carlo algorithm. The behavior of the correlation length $\xi$, the susceptibility at the ordering wavevector $\chi(\bf Q)$, and the spin stiffness $\rho$ clearly reflects the existence of two temperature regimes -- a high temperature regime $T > T_{th}$, in which the disordering effect of vortices is dominant, and a low temperature regime $T < T_{th}$, where correlations are controlled by small amplitude spin fluctuations. As has previously been shown, in the last regime, the behavior of the above quantities agrees well with the predictions of a renormalization group treatment of the appropriate nonlinear sigma model. For $T > T_{th}$, a satisfactory fit of the data is achieved, if the temperature dependence of $\xi$ and $\chi(\bf Q)$ is assumed to be of the form predicted by the Kosterlitz--Thouless theory. Surprisingly, the crossover between the two regimes appears to happen in a very narrow temperature interval around $T_{th} \simeq 0.28$.Comment: 13 pages, 8 Postscript figure

A mixed methods study of the administration of flucloxacillin oral liquid; identifying strategies to overcome administration issues of medicines with poor palatability.

BackgroundThe palatability of flucloxacillin oral liquid is poor. Parents/carers use strategies to aid the administration of poorly palatable medicines.AimTo assess views on the palatability of flucloxacillin oral liquid and identify factors associated with successful administration.MethodsA mixed methods study which included a structured review of online forums and a survey of parent/carers of children with cystic fibrosis (CF) to obtain parent/carer views on the administration of flucloxacillin oral liquid.ResultsA total of 18 strategies to aid the administration of flucloxacillin suspension to children were identified on 10 different public online forums. A total of 255 responses to the open online survey were received with 47% of respondents reporting that administration of flucloxacillin was more problematic compared to other medicines and 38% reporting the need to improve the palatability. The brand of flucloxacillin oral liquid significantly influenced the degree of difficulty associated with administration to children. A significant relationship was found between the concentration of flucloxacillin and the reported number of doses successfully administered. The use of food and drink to aid administration was more commonly stated in online forums (44%) compared to the survey data of parents/carers of children with CF (15.9%).ConclusionThe administration of flucloxacillin oral liquid is perceived as a challenge by parent/carers because of palatability. For chronic use, a more concentrated oral liquid and certain brands are likely to improve acceptability

First-Order Transition to Incommensurate Phase with Broken Lattice Rotation Symmetry in Frustrated Heisenberg Model

We study a finite-temperature phase transition in the two-dimensional classical Heisenberg model on a triangular lattice with a ferromagnetic nearest-neighbor interaction $J_1$ and an antiferromagnetic third-nearest-neighbor interaction $J_3$ using a Monte Carlo method. Apart from a trivial degeneracy corresponding to O(3) spin rotations,the ground state for $J_3 \neq 0$ has a threefold degeneracy corresponding to 120 degree lattice rotations. We find that this model exhibits a first-order phase transition with the breaking of the threefold symmetry when the interaction ratio is $J_3/J_1=-3$.Comment: 4pages,5figure

The nature of the different zero-temperature phases in discrete two-dimensional spin glasses: Entropy, universality, chaos and cascades in the renormalization group flow

The properties of discrete two-dimensional spin glasses depend strongly on the way the zero-temperature limit is taken. We discuss this phenomenon in the context of the Migdal-Kadanoff renormalization group. We see, in particular, how these properties are connected with the presence of a cascade of fixed points in the renormalization group flow. Of particular interest are two unstable fixed points that correspond to two different spin-glass phases at zero temperature. We discuss how these phenomena are related with the presence of entropy fluctuations and temperature chaos, and universality in this model.Comment: 14 pages, 5 figures, 2 table