A geometrically exact formulation of peridynamics Javili, Ali; McBride, Andrew T.; Steinmann, Paul
Theoretical and applied fracture mechanics,
February 2021, 2021-02-00, 20210201, Letnik:
111
Journal Article
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•The proposed formulation accounts for large deformations.•The proposed formulation is variationally consistent.•The proposed strategy is fully implicit.•The quadratic rate of convergence of the ...Newton–Raphson scheme is obtained.•The capabilities of the framework are illustrated via examples at large deformations.
The main objective of this contribution is to develop a geometrically exact peridynamics (PD) formulation wherein the basic elements of continuum kinematics are preserved. The proposed formulation accounts for large deformations and is variationally consistent. We distinguish between one-, two- and three-neighbour interactions. One-neighbour interactions recover the original (bond-based) PD formalism. Two- and three-neighbour interactions are fundamentally different to state-based PD. We account for material frame indifference and provide a set of appropriate arguments for objective interaction potentials accordingly. This contribution is presented in a manner such that the established theory is immediately suitable for computational implementation. From a computational perspective, the proposed strategy is fully implicit and the quadratic rate of convergence associated with the Newton–Raphson scheme is observed. Finally, we demonstrate the capability of our proposed framework via a series of numerical examples at large deformations.
The most common complication with reverse shoulder arthroplasty Grammont based design with a 155° neck shaft angle (NSA) is scapular notching. Scapular notching has been associated with reduced ...clinical outcomes. Reducing the humeral NSA from 155° has been shown to reduce the incidence of scapular notching however it is unknown whether there is a difference in scapular notching between a 145° and 135° NSA. The purpose of this study was to evaluate the effect of decreasing the NSA on scapular notching rate and postoperative range of motion comparing 145° and 135° NSA stems at minimum 2 yr of follow-up.
Consecutive patients undergoing primary reverse shoulder arthroplasty with a NSA of either 145° or 135° between January 2014 and February 2019 were retrospectively reviewed. Patients were included if they were over the age of 18, had minimum clinical follow-up of 24 mo with true postoperative anteroposterior radiographic view.
One hundred and three patients were included for the final analysis: 73 with a 145° NSA and 30 with a 135° NSA stem. The mean age and mean follow-up were respectively 70.9 yr (range, 52.0-89.0) and 32.1 mo. The overall incidence of scapular notching was 46.6 %. There was a statistically significant difference in scapular notching between the 145° (53.4%) and 135° (30%) NSA groups (P = .028). There was no difference in terms of postoperative Constant–Murley Score (mean, 66.1 vs. 68.2; P = .395), Subjective Shoulder Value (mean, 76.5 vs. 83.1%, P = .167), forward flexion (mean, 140° vs. 142°, P = .704), abduction (mean, 123.2° vs. 121.5°, P = .771), external rotation with the arm at the side (mean, 34.1° vs. 37.3°, P = .341) and internal rotation (mean, 5.3 vs. 5.4 pts P = .336) between the 2 groups.
This is the first study to compare the effect of a 145° vs. 135° NSA on scapular notching rates. The key finding of this study is that scapular notching rate was significantly reduced from 53% to 30% in 135° NSA compared to 145° NSA, after at least 24 mo of follow-up. Our data also show that glenoid lateralization and inferiorization has an influence on scapular notching. We are unable to state that the reduced scapular notching rate was due to a reduction in NSA alone. Despite a lower rate of scapular notching, the 135° NSA group has not shown any significant better clinical and functional outcomes.
Previous research has indicated that two components of reaching behavior, initiation time and reach curvature, exhibit distinct patterns of trial sequence effects in congruency tasks. The observed ...patterns have been proposed to reflect two dissociable processes underlying decision behavior, with initiation times capturing the functioning of a threshold adjustment process involving the temporary inhibition of motor output, and reach curvatures reflecting a controlled selection process that supports goal-driven stimulus–response translation. The tasks used in previous studies, however, did not control for a range of associative-priming confounds commonly featured in congruency tasks. Consequently, the extent to which the observed patterns reflected the proposed processes or associative-priming confounds remained unclear. We therefore presented 45 adult participants with a reach-tracking version of the Stroop task that featured both confound-minimized and confound-laden trials. Initiation times revealed main effects of previous and current congruency on both confound-minimized and confound-laden trials, consistent with the claim that initiation times can be used to target the functioning of the threshold adjustment process. Conversely, reach curvatures exhibited a clear sensitivity to associative-priming effects, revealing a congruency sequence effect on confound-laden but not on confound-minimized trials. This finding is consistent with the claim that reach curvatures can be used to target the functioning of the controlled selection process. Thus, by directly evaluating the influence of associative-priming confounds, the present study revealed the strongest evidence to date that decision behavior in tasks involving conflict is fundamentally structured by the functioning of two dissociable processes.
The treatment of shoulder osteoarthritis in the young patient remains challenging. The higher functional demands and higher expectations of the young patient cohort are often coupled with increased ...failure and revision rates. Consequently, shoulder surgeons are faced with a unique challenge with implant selection. The aim of this study was to compare the survivorship and reasons for revision of 5 classes of shoulder arthroplasty in patients aged <55 years with a primary diagnosis of osteoarthritis by use of data from a large national arthroplasty registry.
The study population included all primary shoulder arthroplasty procedures undertaken for osteoarthritis in patients aged <55 years and reported to the registry between September 1999 and December 2021. Procedures were grouped into the following classes: total shoulder arthroplasty (TSA), hemiarthroplasty resurfacing (HRA), hemiarthroplasty stemmed metallic head (HSMH), hemiarthroplasty stemmed pyrocarbon head (HSPH), and reverse total shoulder arthroplasty (RTSA). The outcome measure was the cumulative percent revision, which was defined using Kaplan-Meier estimates of survivorship to describe the time to the first revision. Hazard ratios (HRs) were calculated from Cox proportional hazards models, adjusting for age and sex, to compare revision rates among groups.
There were 1564 shoulder arthroplasty procedures in patients aged <55 years, of which 361 (23.1%) were HRA, 70 (4.5%) were HSMH, 159 (10.2%) were HSPH, 714 (45.7%) were TSA, and 260 (16.6%) were RTSA. HRA had a higher rate of revision than RTSA after 1 year (HRA = 2.51 (95% CI 1.30, 4.83), P = .005), with no difference prior to that time. In addition, HSMH had a higher rate of revision than RTSA for the entire period (HR, 2.69 95% confidence interval, 1.28-5.63, P = .008). There was no significant difference in the rate of revision for HSPH and TSA when they were compared with RTSA. Glenoid erosion was the most common cause of revision for HRA (28.6% of revisions) and HSMH (50%). Instability/dislocation was the leading cause of revision for RTSA (41.7%) and HSPH (28.6%), and for TSA, the majority of revisions were for either instability/dislocation (20.6%) or loosening (18.6%).
These results should be interpreted within the context of the lack of availability of long-term data on RTSA and HSPH stems. RTSA outperforms all implants regarding revision rates at mid-term follow-up. The high early dislocation rate associated with RTSA, as well as the lack of revision options available to address this, indicates that careful selection of patients and a greater appreciation of anatomic risk factors are needed in the future.
A new class of implicit‐explicit (IMEX) methods combined with a p$$ p $$‐adaptive mixed finite element formulation is proposed to simulate the diffusion of reacting species. Hierarchical polynomial ...functions are used to construct a conforming base for the flux vectors, and a non‐conforming base for the mass concentration of the species. The mixed formulation captures the distinct nonlinearities associated with the flux constitutive equations and the reaction terms. The IMEX method conveniently treats these two sources of nonlinearity implicitly and explicitly, respectively, within a single time‐stepping framework. A reliable a posteriori error estimate is proposed and analyzed. A p$$ p $$‐adaptive algorithm based on the proposed a posteriori error estimate is also constructed. The combination of the proposed residual‐based a posteriori error estimate and hierarchical finite element spaces allows for the formulation of an efficient p$$ p $$‐adaptive algorithm. A series of numerical examples demonstrate the performance of the approach for problems involving travelling waves, and possessing discontinuities and singularities. The flexibility of the formulation is illustrated via selected applications in pattern formation and electrophysiology.
Standard low-order finite elements, which perform well for problems involving compressible elastic materials, are known to under-perform when nearly incompressible materials are involved, commonly ...exhibiting the locking phenomenon. Interior penalty (IP) discontinuous Galerkin methods have been shown to circumvent locking when simplicial elements are used. The same IP methods, however, result in locking on meshes of quadrilaterals. The authors have shown in earlier work that under-integration of specified terms in the IP formulation eliminates the locking problem for rectangular elements. Here it is demonstrated through an extensive numerical investigation that the effect of using under-integration carries over successfully to meshes of more general quadrilateral elements, as would likely be used in practical applications, and results in accurate displacement approximations. Uniform convergence with respect to the compressibility parameter is shown numerically. Additionally, a stress approximation obtained here by postprocessing shows good convergence in the incompressible limit.
•A discontinuous Galerkin method to overcome volumetric locking is analysed•Extensive numerical examples are given for quadrilateral/hexahedral meshes•Uniform convergence with respect to element shape regularity is observed•Stress fields obtained by postprocessing yield good convergence results
A novel implicit integration scheme for the Discrete Element Method (DEM) based on the variational integrator approach is presented. The numerical solver provides a fully dynamical description that, ...notably, reduces to an energy minimisation scheme in the quasi-static limit. A detailed derivation of the numerical method is presented for the Hookean contact model and tested against an established open source DEM package that uses the velocity-Verlet integration scheme. These tests compare results for a single collision, long-term stability and statistical quantities of ensembles of particles. Numerically, the proposed integration method demonstrates equivalent accuracy to the velocity-Verlet method.
•An implicit integration scheme for the Discrete Element Method based on the variational integrator approach is presented.•Numerically, the proposed integration method demonstrates equivalent accuracy to the established methods.•This work is inspired by the Quasicontinuum Method and is seen as a crucial step towards a granular Quasicontinuum Method.
Stress fractures of the upper limb affect athletes from a wide range of sports. Athletes involved in throwing sports are particularly susceptible along with athletes from sports involving high ...repetitive and compressive loads such as gymnastics. Diagnosis can be made from clinical history, examination and radiography in some cases however MRI imaging is often required for definitive diagnosis. The mainstay of management is rest and activity modification however advanced pathology often requires surgical management for successful resolution and return to play. In the elbow, the bones susceptible to excessive stress in sport are the distal humerus, the olecranon process of the ulna, the coronoid process of the ulna, the sublime tubercle and the radial head. In immature patients, medial epicondyle apophysis is the most common location. The article presents a narrative review of the literature.
Steroid concentrations within tissues are modulated by intracellular enzymes. Such "steroid intracrinology" influences hormone-dependent cancers and obesity and provides targets for pharmacological ...inhibition. However, no high resolution methods exist to quantify steroids within target tissues. We developed mass spectrometry imaging (MSI), combining matrix assisted laser desorption ionization with on-tissue derivatization with Girard T and Fourier transform ion cyclotron resonance mass spectrometry, to quantify substrate and product (11-dehydrocorticosterone and corticosterone) of the glucocorticoid-amplifying enzyme 11β-HSD1. Regional steroid distribution was imaged at 150-200 μm resolution in rat adrenal gland and mouse brain sections and confirmed with collision induced dissociation/liquid extraction surface analysis. In brains of mice with 11β-HSD1 deficiency or inhibition, MSI quantified changes in subregional corticosterone/11-dehydrocorticosterone ratio, distribution of inhibitor, and accumulation of the alternative 11β-HSD1 substrate, 7-ketocholesterol. MSI data correlated well with LC-MS/MS in whole brain homogenates. MSI with derivatization is a powerful new tool to investigate steroid biology within tissues.
Stimulant psychosis: systematic review Curran, Catherine; Byrappa, Neetha; McBride, Andrew
British journal of psychiatry,
09/2004, Letnik:
185
Journal Article
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Psychosis associated with stimulant use is an increasing problem, but there is little research evidence about the nature of the problem and its management.
To critically review the literature on ...stimulant psychosis and sensitisation.
Systematic review of studies that have investigated stimulant use and psychosis in humans. The main outcome measures were increases in psychosis with stimulant use, and differences between stimulant users and non-users.
Fifty-four studies met the inclusion criteria. Experimental studies show that a single dose of a stimulant drug can produce a brief increase in psychosis ratings (a "response") in 50-70% of participants with schizophrenia and pre-existing acute psychotic symptoms, unaffected by the presence of antipsychotic medication. Those with schizophrenia who do not have acute psychotic symptoms respond, but less frequently (30%). There has been little research into the longer-term effects of use.
Compliance with antipsychotic medication by someone with schizophrenia will not prevent a relapse or worsening of psychotic symptoms if stimulants are used. Low-dose antipsychotic treatment may be beneficial in stimulant users, to prevent sensitisation.
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