Numerical analysis of a transmission problem with Signorini contact using mixed-FEM and BEM

© EDP Sciences, SMAI 2011This paper is concerned with the dual formulation of the interface problem consisting of a linear partial differential equation with variable coefficients in some bounded Lipschitz domain Ω in Rn (n ≥ 2) and the Laplace equation with some radiation condition in the unbounded exterior domain Ωc := Rn\￣Ω. The two problems are coupled by transmission and Signorini contact conditions on the interface Γ = ∂Ω. The exterior part of the interface problem is rewritten using a Neumann to Dirichlet mapping (NtD) given in terms of boundary integral operators. The resulting variational formulation becomes a variational inequality with a linear operator. Then we treat the corresponding numerical scheme and discuss an approximation of the NtD mapping with an appropriate discretization of the inverse Poincar´e-Steklov operator. In particular, assuming some abstract approximation properties and a discrete inf-sup condition, we show unique solvability of the discrete scheme and obtain the corresponding a-priori error estimate. Next, we prove that these assumptions are satisfied with Raviart- Thomas elements and piecewise constants in Ω, and continuous piecewise linear functions on Γ. We suggest a solver based on a modified Uzawa algorithm and show convergence. Finally we present some numerical results illustrating our theory

Complex instantons in sigma models with chemical potential

We analyze two-dimensional nonlinear sigma models at nonzero chemical potentials, which are governed by a complex action. In the spirit of contour deformations (thimbles), we extend the fields into the complex plane, which allows us to incorporate the chemical potentials mu as twisted boundary conditions. We write down the equations of motion and find exact BPS-like solutions in terms of pairs of (anti) holomorphic functions, in particular generalizations of unit charge and fractional instantons to generic mu. The decay of these solutions is controlled by the imaginary part of mu and a vanishing imaginary part causes jumps in the action. We analyze how the total charge is distributed into localized objects and to what extent these are characterized by topology

Generalizability and reach of a randomized controlled trial to improve oral health among home care recipients: comparing participants and nonparticipants at baseline and during follow-up

Background The generalizability of randomized controlled trials (RCTs) with a low response can be limited by systematic differences between participants and nonparticipants. This participation bias, however, is rarely investigated because data on nonparticipants is usually not available. The purpose of this article is to compare all participants and nonparticipants of a RCT to improve oral health among home care recipients at baseline and during follow-up using claims data. Methods Seven German statutory health and long-term care insurance funds invited 9656 home care recipients to participate in the RCT MundPflege. Claims data for all participants (n = 527, 5.5% response) and nonparticipants (n = 9129) were analyzed. Associations between trial participation and sex, age, care dependency, number of Elixhauser diseases, and dementia, as well as nursing, medical, and dental care utilization at baseline, were investigated using multivariable logistic regression. Associations between trial participation and the probability of (a) moving into a nursing home, (b) being hospitalized, and (c) death during 1 year of follow-up were examined via Cox proportional hazards regressions, controlling for baseline variables. Results At baseline, trial participation was positively associated with male sex (odds ratio 1.29 [95% confidence interval 1.08–1.54]), high (vs. low 1.46 [1.15–1.86]) care dependency, receiving occasional in-kind benefits to relieve caring relatives (1.45 [1.15–1.84]), having a referral by a general practitioner to a medical specialist (1.62 [1.21–2.18]), and dental care utilization (2.02 [1.67–2.45]). It was negatively associated with being 75–84 (vs. < 60 0.67 [0.50–0.90]) and 85 + (0.50 [0.37–0.69]) years old. For morbidity, hospitalizations, and formal, respite, short-term, and day or night care, no associations were found. During follow-up, participants were less likely to move into a nursing home than nonparticipants (hazard ratio 0.50 [0.32–0.79]). For hospitalizations and mortality, no associations were found. Conclusions For half of the comparisons, differences between participants and nonparticipants were observed. The RCT’s generalizability is limited, but to a smaller extent than one would expect because of the low response. Routine data provide a valuable source for investigating potential differences between trial participants and nonparticipants, which might be used by future RCTs to evaluate the generalizability of their findings. Trial registrati German Clinical Trials Register DRKS00013517. Retrospectively registered on June 11, 2018

Image fusion of coronary CT angiography and cardiac perfusion MRI: a pilot study

Objective: To develop a tool for the image fusion of computed tomography coronary angiography (CTCA) and cardiac magnetic resonance imaging (CMR). Methods: Surface representations and volume-rendered images from fused CTCA/CMR data of five patients with significant coronary artery disease (CAD) on CTCA and perfusion deficits on CMR were generated using a newly developed software prototype. The spatial relationship of significant coronary artery stenosis at CTCA and myocardial defects at CMR was evaluated. Results: Registration of CTCA and CMR images was possible in all patients. The comprehensive three-dimensional visualisation of fused CTCA and CMR data accurately demonstrated the relationship between coronary artery stenoses and myocardial defects in all patients. Conclusion: The introduced tool enables image fusion of CTCA and CMR data sets and allows for correct superposition of the coronary arteries derived from CTCA onto the corresponding myocardial segments derived from CMR. The method facilitates the comprehensive assessment of the functionally relevant CAD by the exact allocation of culprit coronary stenoses to corresponding myocardial defects at a low radiation dos

Total arterial off-pump surgery provides excellent outcomes and does not compromise complete revascularization†

OBJECTIVES The combination of aortic ‘no-touch' off-pump surgery (OPCAB) and total arterial revascularization (TAR) can reduce peri-procedural morbidity and yields excellent long-term outcomes albeit at a reported risk of incomplete revascularization. The feasibility of OPCAB-TAR with specific regards to the complete revascularization (CR) in patients with multi-vessel disease was evaluated. METHODS From 2003 to 2010, 712 patients underwent TAR including 526 patients who had OPCAB-TAR and 186 patients who received on-pump TAR [(ONCAB grafting (ONCABG)-TAR)]. Of these, 52% (n=272; OPCAB) vs. 83% (n=155; ONCABG) had triple-vessel disease (TVD). To balance patient characteristics, a non-parsimonious, propensity score (PS) model was applied. Endpoints evaluated were mortality, stroke, major adverse cardiac and cerebrovascular events (MACCE). To evaluate CR, an ‘Index of CR' (ICOR) was calculated, defined as the number of distal anastomoses divided by the number of the diseased coronary vessels. CR was assumed when the following requirements were fulfilled: the number of distal anastomoses was equal to or higher than that of diseased vessels (ICOR≥1), and all affected coronary territories (left anterior descending, circumflex artery and/or right coronary artery) were grafted. RESULTS Mortality was comparable between groups, whereas OPCAB patients suffered from significantly decreased rates of MACCE [3.0 vs. 7.0%; propensity-adjusted odd ratio (PAOR)=0.24; confidence interval (CI) 95% 0.08-0.66; P=0.006] including a clear trend towards reduced stroke and myocardial infarction. In the subgroup with TVD, OPCAB patients presented with significantly reduced rates for MACCE (1.8 vs. 5.8%; PAOR=0.07; CI 95% 0.01-0.65; P=0.02), including a significantly lower rate for stroke. For all-comers, the number of diseased vessels was lower after OPCAB (2.36±0.73 vs. 2.87±0.39; P<0.001) and consequently, these patients received an overall lower number of distal anastomoses (2.42±1.15 vs. 3.06±0.98; P<0.001). Although the ICOR was slightly lower (1.04±0.37 vs. 1.07±0.37; P=0.02), CR was achieved more frequently in OPCAB patients (82.1 vs. 73.1%; P=0.01). In the subgroup with TVD, the number of distal anastomoses (2.99±1.14 vs. 3.10±0.98; P=0.19) and the ICOR (1.00±0.38 vs. 1.03±0.33; P=0.19) was comparable between groups. The frequency of CR was slightly higher (75 vs. 67.7%; P=0.11), and the proportion of complete in situ grafting was significantly higher after OPCAB (37.1 vs. 23.9%; P=0.005). CONCLUSIONS Aortic ‘no-touch' OPCAB-TAR leads to a significant reduction of MACCE. It does not compromise CR in patients with TVD and thus can be safely applied to these patient

Total arterial off-pump surgery provides excellent outcomes and does not compromise complete revascularization†

OBJECTIVES The combination of aortic ‘no-touch' off-pump surgery (OPCAB) and total arterial revascularization (TAR) can reduce peri-procedural morbidity and yields excellent long-term outcomes albeit at a reported risk of incomplete revascularization. The feasibility of OPCAB-TAR with specific regards to the complete revascularization (CR) in patients with multi-vessel disease was evaluated. METHODS From 2003 to 2010, 712 patients underwent TAR including 526 patients who had OPCAB-TAR and 186 patients who received on-pump TAR [(ONCAB grafting (ONCABG)-TAR)]. Of these, 52% (n=272; OPCAB) vs. 83% (n=155; ONCABG) had triple-vessel disease (TVD). To balance patient characteristics, a non-parsimonious, propensity score (PS) model was applied. Endpoints evaluated were mortality, stroke, major adverse cardiac and cerebrovascular events (MACCE). To evaluate CR, an ‘Index of CR' (ICOR) was calculated, defined as the number of distal anastomoses divided by the number of the diseased coronary vessels. CR was assumed when the following requirements were fulfilled: the number of distal anastomoses was equal to or higher than that of diseased vessels (ICOR≥1), and all affected coronary territories (left anterior descending, circumflex artery and/or right coronary artery) were grafted. RESULTS Mortality was comparable between groups, whereas OPCAB patients suffered from significantly decreased rates of MACCE [3.0 vs. 7.0%; propensity-adjusted odd ratio (PAOR)=0.24; confidence interval (CI) 95% 0.08-0.66; P=0.006] including a clear trend towards reduced stroke and myocardial infarction. In the subgroup with TVD, OPCAB patients presented with significantly reduced rates for MACCE (1.8 vs. 5.8%; PAOR=0.07; CI 95% 0.01-0.65; P=0.02), including a significantly lower rate for stroke. For all-comers, the number of diseased vessels was lower after OPCAB (2.36±0.73 vs. 2.87±0.39; P<0.001) and consequently, these patients received an overall lower number of distal anastomoses (2.42±1.15 vs. 3.06±0.98; P<0.001). Although the ICOR was slightly lower (1.04±0.37 vs. 1.07±0.37; P=0.02), CR was achieved more frequently in OPCAB patients (82.1 vs. 73.1%; P=0.01). In the subgroup with TVD, the number of distal anastomoses (2.99±1.14 vs. 3.10±0.98; P=0.19) and the ICOR (1.00±0.38 vs. 1.03±0.33; P=0.19) was comparable between groups. The frequency of CR was slightly higher (75 vs. 67.7%; P=0.11), and the proportion of complete in situ grafting was significantly higher after OPCAB (37.1 vs. 23.9%; P=0.005). CONCLUSIONS Aortic ‘no-touch' OPCAB-TAR leads to a significant reduction of MACCE. It does not compromise CR in patients with TVD and thus can be safely applied to these patient