Universality in three-dimensional Ising spin glasses: Nonequilibrium dynamics from Monte Carlo simulations

The non-equilibrium dynamics of the three-dimensional Edwards-Anderson spin-glass model with different bond distributions is investigated by means of Monte Carlo simulation. A numerical method is used to determine the critical temperature and the scaling exponents of the correlation and the integrated response functions. The results obtained agree with those calculated in equilibrium simulations and suggest that the universality class does not depend on the exact form of the bond distribution.Comment: 4 pages, 5 figure

An exploration of change and 'borderline personality disorder (BPD)'

The objective of this study was to explore personal experiences of change of people diagnosed with borderline personality disorder (BPD) who had partaken in psychological therapy. The aim was to develop the first model of change grounded in service user experience so that this could inform recovery-oriented practice in relation to this client group. A constructivist grounded theory design was chosen. Eight people with a diagnosis of BPD who had completed group-based therapy programmes or were currently attending a peer support group were interviewed about their experiences of change using a semi-structured, open-ended format. An initial model was developed and refined through triangulation with three published accounts of experiences of change in the context of a BPD diagnosis. ‘Discovering “new ways of being” in interpersonal space’ was conceptualised as the core process underpinning pertinent activities and experiences relating to change in people diagnosed with BPD. This interactive, relational process was facilitated in environments that were felt to be both containing and open to conflict. It involved increasing levels of self-disclosure, information exchange, exploration of mental states, experimentation with new behaviours and the consolidation of new ways of being. The core process appeared to extend beyond the therapeutic setting if supported through a relationship with a secure base. Regardless of therapeutic allegiance, effective interventions for people diagnosed with BPD might share a common core change process. Further research is required into change processes in the context of individual psychological therapies and negative therapeutic experiences

An aeroacoustic investigation into the effect of self-oscillating trailing edge flaplets

The aeroacoustics of a NACA 0012 aerofoil with an array of self-oscillating flexible flaplets attached on the trailing edge has been investigated at low to moderate chord based Reynolds number (50,000 -- 350,000) and at geometric angles of attack from $\alpha_g = 0^\circ$ -- $20^\circ$. When the aerofoil is untripped, tonal peaks are observed on the baseline aerofoil. When the passive flaplets are attached to the pressure side of the aerofoil, the tonal peak is removed. If the flaplets are then placed on the suction side, the tonal peak is reduced, but not removed. It is therefore hypothesised that the flaplets on the pressure side modifies the laminar separation bubble situated on the pressure side of the aerofoil, a key mechanism for tonal noise. Throughout all cases, both tripped and untripped, a low frequency (0.1 kHz -- 0.6 kHz) noise reduction and a slight increase at higher frequencies (>2 kHz) is seen. This gives an average overall sound pressure level (OSPL) reduction of 1.5 -- 2 dB for the flaplets affixed to the pressure side. The cases where the tonal noise component is removed an OSPL reduction of up to 20 dB can be seen

Vortex Shedding and Modal Behavior of a Circular Cylinder Equipped with Flexible Flaps

When a cylinder is subject to a flow, vortices will be shed that can lead to strong tonal noise. The modification of the cylinder with soft, flexible flaps made of silicone rubber has been shown to affect the vortex shedding cycle in a way that the Strouhal number associated with the vortex shedding suddenly jumps to a higher value at a certain Reynolds number. In the present study, the effect of the flexible flaps on the vortex shedding is further examined by subsequently reducing the number of flaps and additionally shortening their length. Acoustic measurements and camera recordings of the flap motion, performed in an aeroacoustic wind tunnel, suggest that the sudden jump of the Reynolds number is caused by the movement of the outer flaps. A comparison with the eigenfrequencies obtained from a numerical modal analysis of the different flap rings revealed that the cause of the Strouhal number jump is most likely a lock-in of the natural vortex shedding cycle with the next higher eigenfrequency of the outer flaps

Study of the de Almeida-Thouless line using power-law diluted one-dimensional Ising spin glasses

We test for the existence of a spin-glass phase transition, the de Almeida-Thouless line, in an externally-applied (random) magnetic field by performing Monte Carlo simulations on a power-law diluted one-dimensional Ising spin glass for very large system sizes. We find that an Almeida-Thouless line only occurs in the mean field regime, which corresponds, for a short-range spin glass, to dimension d larger than 6.Comment: 4 pages, 2 figures, 1 tabl

Population Annealing with Weighted Averages: A Monte Carlo Method for Rough Free Energy Landscapes

The population annealing algorithm introduced by Hukushima and Iba is described. Population annealing combines simulated annealing and Boltzmann weighted differential reproduction within a population of replicas to sample equilibrium states. Population annealing gives direct access to the free energy. It is shown that unbiased measurements of observables can be obtained by weighted averages over many runs with weight factors related to the free energy estimate from the run. Population annealing is well suited to parallelization and may be a useful alternative to parallel tempering for systems with rough free energy landscapes such as spin glasses. The method is demonstrated for spin glasses.Comment: 9 pages, 5 figures; version 2 has improved figure 5 and new titl

Strengths and Weaknesses of Parallel Tempering

Parallel tempering, also known as replica exchange Monte Carlo, is studied in the context of two simple free energy landscapes. The first is a double well potential defined by two macrostates separated by a barrier. The second is a `golf course' potential defined by microstates having two possible energies with exponentially more high energy states than low energy states. The equilibration time for replica exchange is analyzed for both systems. For the double well system, parallel tempering with a number of replicas that scales as the square root of the barrier height yields exponential speedup of the equilibration time. On the other hand, replica exchange yields only marginal speed-up for the golf course system. For the double well system, the free energy difference between the two wells has a large effect on the equilibration time. Nearly degenerate wells equilibrate much more slowly than strongly asymmetric wells. It is proposed that this difference in equilibration time may lead to a bias in measuring overlaps in spin glasses. These examples illustrate the strengths and weaknesses of replica exchange and may serve as a guide for understanding and improving the method in various applications.Comment: 18 pages, 4 figures. v2: typos fixed and wording changes to improve clarit

Observations of comet Levy 1990c in the (OI) 6300-A line with an imaging Fabry-Perot

We have observed the comet Levy 1990c during 16-25 August 1990 using the MPAE focal reducer system based Fabry-Perot etalon coupled with the 1 meter telescope of the Observatory of Hoher List. The free spectral range and resolution limit of the interferometer was approximately 2.18 A and approximately 0.171 A respectively. Classical Fabry-Perot fringes were recorded on a CCD in the cometary (OI) 6300 A line. They are well resolved from telluric air glow and cometary NH2 emission. Our observations indicate that the (OI) is distributed asymmetrically with respect to the center of the comet. In this paper we report the spatial distribution of (OI) emission and its line width in the coma of comet Levy