An adaptive Metropolis-Hastings scheme: sampling and optimization

We propose an adaptive Metropolis-Hastings algorithm in which sampled data are used to update the proposal distribution. We use the samples found by the algorithm at a particular step to form the information-theoretically optimal mean-field approximation to the target distribution, and update the proposal distribution to be that approximatio. We employ our algorithm to sample the energy distribution for several spin-glasses and we demonstrate the superiority of our algorithm to the conventional MH algorithm in sampling and in annealing optimization.Comment: To appear in Europhysics Letter

Hybrid Local-Order Mechanism for Inversion Symmetry Breaking

Using classical Monte Carlo simulations, we study a simple statistical mechanical model of relevance to the emergence of polarisation from local displacements on the square and cubic lattices. Our model contains two key ingredients: a Kitaev-like orientation-dependent interaction between nearest neighbours, and a steric term that acts between next-nearest neighbours. Taken by themselves, each of these two ingredients is incapable of driving long-range symmetry breaking, despite the presence of a broad feature in the corresponding heat capacity functions. Instead each component results in a "hidden" transition on cooling to a manifold of degenerate states, the two manifolds are different in the sense that they reflect distinct types of local order. Remarkably, their intersection---\emph{i.e.} the ground state when both interaction terms are included in the Hamiltonian---supports a spontaneous polarisation. In this way, our study demonstrates how local ordering mechanisms might be combined to break global inversion symmetry in a manner conceptually similar to that operating in the "hybrid" improper ferroelectrics. We discuss the relevance of our analysis to the emergence of spontaneous polarisation in well-studied ferroelectrics such as BaTiO$_3$ and KNbO$_3$.Comment: 8 pages, 8 figure

Algebraic-geometrical formulation of two-dimensional quantum gravity

We find a volume form on moduli space of double punctured Riemann surfaces whose integral satisfies the Painlev\'e I recursion relations of the genus expansion of the specific heat of 2D gravity. This allows us to express the asymptotic expansion of the specific heat as an integral on an infinite dimensional moduli space in the spirit of Friedan-Shenker approach. We outline a conjectural derivation of such recursion relations using the Duistermaat-Heckman theorem.Comment: 10 pages, Latex fil

The value of the follow-through derives from motor learning depending on future actions.

In ball sports, we are taught to follow through, despite the inability of events after contact or release to influence the outcome [1, 2]. Here we show that the specific motor memory active at any given moment critically depends on the movement that will be made in the near future. We demonstrate that associating a different follow-through movement with two motor skills that normally interfere [3-7] allows them to be learned simultaneously, suggesting that distinct future actions activate separate motor memories. This implies that when learning a skill, a variable follow-through would activate multiple motor memories across practice, whereas a consistent follow-through would activate a single motor memory, resulting in faster learning. We confirm this prediction and show that such follow-through effects influence adaptation over time periods associated with real-world skill learning. Overall, our results indicate that movements made in the immediate future influence the current active motor memory. This suggests that there is a critical time period both before [8] and after the current movement that determines motor memory activation and controls learning.This is the final published version. The article was originally published in Current Biology, Volume 25, Issue 3, p397–401, 2 February 2015, DOI: 10.1016/j.cub.2014.12.03

The challenge of ensuring affordability, sustainability, consistency, and adaptability in the common metrics agenda

Summary Mental health research grapples with research waste and stunted field progression caused by inconsistent outcome measurement across studies and clinical settings, which means there is no common language for considering findings. Although recognising that no gold standard measures exist and that all existing measures are flawed in one way or another, anxiety and depression research is spearheading a common metrics movement to harmonise measurement, with several initiatives over the past 5 years recommending the consistent use of specific scales to allow read-across of measurements between studies. For this approach to flourish, however, common metrics must be acceptable and adaptable to a range of contexts and populations, and global access should be as easy and affordable as possible, including in low-income countries. Within a measurement landscape dominated by fixed proprietary measures and with competing views of what should be measured, achieving this goal poses a range of challenges. In this Personal View, we consider tensions between affordability, sustainability, consistency, and adaptability that, if not addressed, risk undermining the common metrics agenda. We outline a three-pronged way forward that involves funders taking more direct responsibility for measure development and dissemination; a move towards managing measure dissemination and adaptation via open-access measure hubs; and transitioning from fixed questionnaires to item banks. We argue that now is the time to start thinking of mental health metrics as 21st century tools to be co-owned and co-created by the mental health community, with support from dedicated infrastructure, coordinating bodies, and funders

Systematic Review and Meta-Analysis: Outcomes of Routine Specialist Mental Health Care for Young People With Depression and/or Anxiety

Objective: Depression and anxiety are the most prevalent mental health problems in youth, yet almost nothing is known about what outcomes are to be expected at the individual level following routine treatment. This paper sets out to address this gap by undertaking a systematic review of outcomes following treatment as usual (TAU) with a particular focus on individual-level outcomes. / Method: MEDLINE, Embase and PsycInfo were searched for articles published between 1980 and January 2019 that assessed TAU outcomes for youth depression and anxiety accessing specialist mental healthcare. Meta-analysis considered change at both group-level pre-post effect size (ES) and individual-level recovery, reliable change and reliable recovery. Temporal analysis considered stability of primary and secondary outcomes over time. Sub-group analysis considered the moderating effect of informant; presenting problem; study design; study year; mean age of youth; use of medication; intervention dosage and type of treatment offered on outcomes. A protocol was pre-registered on PROSPERO (CRD42017063914). / Results: Initial screening of 6,350 publications resulted in 38 which met the inclusion criteria, and which were subsequently included in meta-analyses. This resulted in a final full pooled sample of 11,739 young people (61% of which were female, mean age 13.8 years). The pre-post ES (Hedges’ g) at first/final outcome (13/ 26 weeks) was -0.74/- 0.87. The individual-level change on measures of self-report was 38% reliable improvement, 44% no reliable change and 6% reliable deterioration. Outcomes varied according to moderators, informant, problem type and dosage. / Conclusion: Poor data quantity and quality are limitations, but this is the first study that indicates likely rates of reliable improvement for those accessing TAU. We propose the need for improved reporting of both individual-level metrics and details of TAU to enable greater understanding of likely current outcomes from routine care for youth with depression and anxiety in order to allow the potential for further improvement of impact

A scoping review and assessment of essential elements of shared decision-making of parent-involved interventions in child and adolescent mental health

Parents play a critical role in child and adolescent mental health care and treatment. With the increasing implementation of shared decision-making (SDM) across health settings, there is a growing need to understand the decision support interventions used to promote SDM in child and adolescent mental health services (CAMHS). The overall aim of this review is to identify and examine the existing decision support interventions available for parents. A broad search was conducted using the key concepts "shared decision-making", "parents" and "child and adolescent mental health". Five electronic databases were searched: PsycInfo, Embase, Medline, Web of Science and the Cochrane Library. In addition to these relevant databases, we searched the Ottawa's Inventory of Decision Aids, Children's Hospital of Eastern Ontario website, Google, Google Play and known CAMHS' websites. The search identified 23 interventions available for use with parents. These interventions targeted parents providing care for children with ADHD, ASD, emotional and behavioural problems including depression (EBD), self-harm or universal mental health care. Various modalities including face-to-face, digital and paper-based versions were adopted. The majority of the interventions were able to "present options" (87%) and "discuss the pros and cons" (83%) of treatment. Time, accessibility and appropriateness of the intervention emerged as factors influencing usage and implementation of interventions. Our findings suggest that SDM interventions involving parents have been implemented differently across various presenting mental health difficulties in CAMHS. This review brings awareness of existing parent-involved interventions and has implications for the development, implementation and usage of new interventions

Black Hole Thermodynamics and Riemann Surfaces

We use the analytic continuation procedure proposed in our earlier works to study the thermodynamics of black holes in 2+1 dimensions. A general black hole in 2+1 dimensions has g handles hidden behind h horizons. The result of the analytic continuation is a hyperbolic 3-manifold having the topology of a handlebody. The boundary of this handlebody is a compact Riemann surface of genus G=2g+h-1. Conformal moduli of this surface encode in a simple way the physical characteristics of the black hole. The moduli space of black holes of a given type (g,h) is then the Schottky space at genus G. The (logarithm of the) thermodynamic partition function of the hole is the Kaehler potential for the Weil-Peterson metric on the Schottky space. Bekenstein bound on the black hole entropy leads us to conjecture a new strong bound on this Kaehler potential.Comment: 17+1 pages, 9 figure

Integration of visual and joint information to enable linear reaching motions

A new dynamics-driven control law was developed for a robot arm, based on the feedback control law which uses the linear transformation directly from work space to joint space. This was validated using a simulation of a two-joint planar robot arm and an optimisation algorithm was used to find the optimum matrix to generate straight trajectories of the end-effector in the work space. We found that this linear matrix can be decomposed into the rotation matrix representing the orientation of the goal direction and the joint relation matrix (MJRM) representing the joint response to errors in the Cartesian work space. The decomposition of the linear matrix indicates the separation of path planning in terms of the direction of the reaching motion and the synergies of joint coordination. Once the MJRM is numerically obtained, the feedfoward planning of reaching direction allows us to provide asymptotically stable, linear trajectories in the entire work space through rotational transformation, completely avoiding the use of inverse kinematics. Our dynamics-driven control law suggests an interesting framework for interpreting human reaching motion control alternative to the dominant inverse method based explanations, avoiding expensive computation of the inverse kinematics and the point-to-point control along the desired trajectories

A simple two-module problem to exemplify building-block assembly under crossover

Theoretically and empirically it is clear that a genetic algorithm with crossover will outperform a genetic algorithm without crossover in some fitness landscapes, and vice versa in other landscapes. Despite an extensive literature on the subject, and recent proofs of a principled distinction in the abilities of crossover and non-crossover algorithms for a particular theoretical landscape, building general intuitions about when and why crossover performs well when it does is a different matter. In particular, the proposal that crossover might enable the assembly of good building-blocks has been difficult to verify despite many attempts at idealized building-block landscapes. Here we show the first example of a two-module problem that shows a principled advantage for cross-over. This allows us to understand building-block assembly under crossover quite straightforwardly and build intuition about more general landscape classes favoring crossover or disfavoring it