The Breakdown of Linear Elastic Fracture Mechanics near the Tip of a Rapid Crack

We present high resolution measurements of the displacement and strain fields near the tip of a dynamic (Mode I) crack. The experiments are performed on polyacrylamide gels, brittle elastomers whose fracture dynamics mirror those of typical brittle amorphous materials. Over a wide range of propagation velocities ($0.2-0.8c_s$), we compare linear elastic fracture mechanics (LEFM) to the measured near-tip fields. We find that, sufficiently near the tip, the measured stress intensity factor appears to be non-unique, the crack tip significantly deviates from its predicted parabolic form, and the strains ahead of the tip are more singular than the $r^{-1/2}$ divergence predicted by LEFM. These results show how LEFM breaks down as the crack tip is approached.Comment: 4 pages, 4 figures, first of a two-paper series (experiments); no change in content, minor textual revision

A Computational Account of Borderline Personality Disorder: Impaired Predictive Learning about Self and Others Through Bodily Simulation

Social dysfunction is a prominent and disabling aspect of borderline personality disorder. We reconsider traditional explanations for this problem, especially early disruption in the way an infant feels physical care from its mother, in terms of recent developments in computational psychiatry. In particular, social learning may depend on reinforcement learning though embodied simulations. Such modeling involves calculations based on structures outside the brain such as face and hands, calculations on one\u27s own body that are used to make inferences about others. We discuss ways to test the role of embodied simulation in BPD and potential implications for treatment

Crack Front Waves and the dynamics of a rapidly moving crack

Crack front waves are localized waves that propagate along the leading edge of a crack. They are generated by the interaction of a crack with a localized material inhomogeneity. We show that front waves are nonlinear entities that transport energy, generate surface structure and lead to localized velocity fluctuations. Their existence locally imparts inertia, which is not incorporated in current theories of fracture, to initially "massless" cracks. This, coupled to crack instabilities, yields both inhomogeneity and scaling behavior within fracture surface structure.Comment: Embedded Latex file including 4 figure

Phase-Field Model of Mode III Dynamic Fracture

We introduce a phenomenological continuum model for mode III dynamic fracture that is based on the phase-field methodology used extensively to model interfacial pattern formation. We couple a scalar field, which distinguishes between ``broken'' and ``unbroken'' states of the system, to the displacement field in a way that consistently includes both macroscopic elasticity and a simple rotationally invariant short scale description of breaking. We report two-dimensional simulations that yield steady-state crack motion in a strip geometry above the Griffith threshold.Comment: submitted to PR

Repetitive transcranial magnetic stimulation (r-TMS) and selective serotonin reuptake inhibitor-resistance in obsessive-compulsive disorder: A meta-analysis and clinical implications

Introduction: Despite promising results from several randomized controlled trials (RCTs) and meta-analyses, the efficacy of r-TMS as a treatment for OCD remains controversial, at least in part owing to inconsistency in the trial methodologies and heterogeneity in the trial outcomes. This meta-analysis attempts to explain some of this heterogeneity by comparing the efficacy of r-TMS in patients with or without resistance to treatment with selective serotonin reuptake inhibitors (SSRI), defined using standardized criteria. Methods: We conducted a pre-registered (PROSPERO ID: 241381) systematic review and meta-analysis. English language articles reporting blinded RCTs were retrieved from searches using MEDLINE, PsycINFO, and Cochrane Library databases. Studies were subjected to subgroup analysis based on four stages of treatment resistance, defined using an adaptation of published criteria (1 = not treatment resistant, 2 = one SSRI trial failed, 3 = two SSRI trials failed, 4 = two SSRI trials failed plus one or more CBT trial failed). Meta-regression analyses investigated patient and methodological factors (age, duration of OCD, illness severity, stage of treatment-resistance, or researcher allegiance) as possible moderators of effect size. Results: Twenty-five independent comparisons (23 studies) were included. Overall, r-TMS showed a medium-sized reduction of Yale-Brown Obsessive-Compulsive Scale (Y-BOCS) scores (Hedge's g: -0.47; 95%CI: - 0.67 to −0.27) with moderate heterogeneity (I2 = 39.8%). Assessment of publication bias using Trim and Fill analysis suggested a reduced effect size that remained significant (g: -0.29; 95%CI: −0.51 to −0.07). Subgroup analysis found that those studies including patients non-resistant to SSRI (stage 1) (g: -0.65; 95%CI: −1.05 to −0.25, k = 7) or with low SSRI-resistance (stage 2) (g:-0.47; 95%CI: −0.86 to −0.09, k = 6) produced statistically significant results with low heterogeneity, while studies including more highly resistant patients at stage 3 (g: −0.39; 95%CI: −0.90 to 0.11, k = 4) and stage 4 (g: -0.36; 95%CI: −0.75 to 0.03, k = 8) did not. Intriguingly, the only significant moderator of the effect size found by meta-regression was the severity of baseline depressive symptoms. All trials showed evidence of researcher allegiance in favour of the intervention and therefore caution is required in interpreting the reported effect sizes. Conclusion: This meta-analysis shows that r-TMS is an effective treatment for OCD, but largely for those not resistant to SSRI or failing to respond to only one SSRI trial. As a consequence, r-TMS may be best implemented earlier in the care pathway. These findings would have major implications for clinical service development, but further well-powered RCTs, which eliminate bias from researcher allegiance, are needed before definitive conclusions can be drawn

Screening and assessment tools for gaming disorder: A comprehensive systematic review

The inclusion of gaming disorder (GD) as an official diagnosis in the ICD-11 was a significant milestone for the field. However, the optimal measurement approaches for GD are currently unclear. This comprehensive systematic review aimed to identify and evaluate all available English-language GD tools and their corresponding evidence. A search of PsychINFO, PsychArticles, ScienceDirect, Scopus, Web of Science, and Google Scholar identified 32 tools employed in 320 studies (N = 462,249 participants). The evaluation framework examined tools in relation to: (1) conceptual and practical considerations; (2) alignment with DSM-5 and ICD-11 criteria; (3) type and quantity of studies and samples; and (4) psychometric properties. The evaluation showed that GD instrumentation has proliferated, with 2.5 tools, on average, published annually since 2013. Coverage of DSM-5 and ICD-11 criteria was inconsistent, especially for the criterion of continued use despite harm. Tools converge on the importance of screening for impaired control over gaming and functional impairment. Overall, no single tool was found to be clearly superior, but the AICA-Sgaming, GAS-7, IGDT-10, IGDS9-SF, and Lemmens IGD-9 scales had greater evidential support for their psychometric properties. The GD field would benefit from a standard international tool to identify gaming-related harms across the spectrum of maladaptive gaming behaviors.Peer reviewedFinal Accepted Versio

Meta-analysis of cognitive behaviour therapy and selective serotonin reuptake inhibitors for the treatment of hypochondriasis: Implications for trial design

Background: Classification of hypochondriasis as an obsessive-compulsive and related disorder in the International Classification of Diseases 11th Revision (ICD-11) has generated new heuristics for treatment of this common, chronic and disabling disorder. Standard treatment involves cognitive behaviour therapy (CBT) or selective serotonin reuptake inhibitors (SSRIs), but no meta-analysis has so far considered hypochondriasis as a structured diagnosis or assessed the role of medication. A clearer understanding of the relative effectiveness of these interventions and identification of clinically relevant factors moderating the treatment response is needed for clinical guideline development. Methods: The current systematic review and meta-analysis of interventions for hypochondriasis was preregistered on PROSPERO (CRD42020185768) and follows PRISMA guidelines. We searched MEDLINE, PsycINFO, and Cochrane Library databases until July 2021 for randomized controlled trials (RCTs) of interventions for patients diagnosed with hypochondriasis (or historical diagnostic equivalents). We assessed aspects of study quality using: the CONSORT Checklist for evaluation of RCTs, the Cochrane Risk of Bias 2 tool, researcher allegiance and treatment fidelity. The primary outcome was improvement in hypochondriasis symptoms, comparing intervention and control groups at trial endpoint. Moderator variables were assessed using subgroup and meta-regression analyses. Results: Searches identified 13 randomised controlled trials (RCTs) (N = 1405); 12 included CBT (N = 1212) and three included SSRI (N = 193) arms as the experimental intervention. Random effects meta-analysis yielded a moderate-to-large effect size for CBT versus all controls (g = −0.70 [95% CI -0.99 to −0.41], k = 18, I2 = 81.1%). Funnel plot asymmetry indicated possible publication bias and two potentially missing trials, reducing the effect size (g = −0.60 [95% CI -0.88 to −0.32]). Subgroup analysis showed that choice of control significantly moderated effect size, with those in CBT vs. wait-list (g = −1.32 [95% CI -1.75 to −0.90], k = 7, I2 = 0%) being double those of CBT vs. psychological or pharmacological placebo controls (g = −0.58 [95% CI -0.95 to −0.22], k = 7, I2 = 82%). Analysis of studies directly comparing CBT and SSRIs found a numerical, but not statistical advantage for SSRIs (g = 0.21 [95% CI -0.46 to 0.87], k = 2, I2 = 58.34%) and a modest effect size emerged for SSRIs vs. pill placebo (g = −0.29 [95% CI -0.57 to −0.01], k = 3, I2 = 0%). Most studies (11/13) were rated as high on potential researcher allegiance bias in favour of CBT. Meta-regressions revealed that effect sizes were larger in younger participants, and smaller in better quality and more recent RCTs and those with greater CBT fidelity. Conclusion: CBT and SSRIs are effective in the acute treatment of hypochondriasis, with some indication that intervention at a younger age produces better outcomes for CBT. In the case of CBT, effect sizes appear to have been significantly inflated by the use of wait list controls, and researcher allegiance bias. We recommend that a definitive, adequately controlled trial, designed with respect to the methodological issues raised in this meta-analysis, is needed to determine the magnitude effects for CBT and SSRIs with confidence and the long-term effect of treatments, to inform mental health service provision for this overlooked patient group

Continuum field description of crack propagation

We develop continuum field model for crack propagation in brittle amorphous solids. The model is represented by equations for elastic displacements combined with the order parameter equation which accounts for the dynamics of defects. This model captures all important phenomenology of crack propagation: crack initiation, propagation, dynamic fracture instability, sound emission, crack branching and fragmentation.Comment: 4 pages, 5 figures, submitted to Phys. Rev. Lett. Additional information can be obtained from http://gershwin.msd.anl.gov/theor