Coarse Grained Computations for a Micellar System

We establish, through coarse-grained computation, a connection between traditional, continuum numerical algorithms (initial value problems as well as fixed point algorithms) and atomistic simulations of the Larson model of micelle formation. The procedure hinges on the (expected) evolution of a few slow, coarse-grained mesoscopic observables of the MC simulation, and on (computational) time scale separation between these and the remaining "slaved", fast variables. Short bursts of appropriately initialized atomistic simulation are used to estimate the (coarse-grained, deterministic) local dynamics of the evolution of the observables. These estimates are then in turn used to accelerate the evolution to computational stationarity through traditional continuum algorithms (forward Euler integration, Newton-Raphson fixed point computation). This "equation-free" framework, bypassing the derivation of explicit, closed equations for the observables (e.g. equations of state) may provide a computational bridge between direct atomistic / stochastic simulation and the analysis of its macroscopic, system-level consequences

Coarse-Grained Kinetic Computations for Rare Events: Application to Micelle Formation

We discuss a coarse-grained approach to the computation of rare events in the context of grand canonical Monte Carlo (GCMC) simulations of self-assembly of surfactant molecules into micelles. The basic assumption is that the {\it computational} system dynamics can be decomposed into two parts -- fast (noise) and slow (reaction coordinates) dynamics, so that the system can be described by an effective, coarse grained Fokker-Planck (FP) equation. While such an assumption may be valid in many circumstances, an explicit form of FP equation is not always available. In our computations we bypass the analytic derivation of such an effective FP equation. The effective free energy gradient and the state-dependent magnitude of the random noise, which are necessary to formulate the effective Fokker-Planck equation, are obtained from ensembles of short bursts of microscopic simulations {\it with judiciously chosen initial conditions}. The reaction coordinate in our micelle formation problem is taken to be the size of a cluster of surfactant molecules. We test the validity of the effective FP description in this system and reconstruct a coarse-grained free energy surface in good agreement with full-scale GCMC simulations. We also show that, for very small clusters, the cluster size seizes to be a good reaction coordinate for a one-dimensional effective description. We discuss possible ways to improve the current model and to take higher-dimensional coarse-grained dynamics into account

Stretching Method-Based Operational Modal Analysis of An Old Masonry Lighthouse.

We present in this paper a structural health monitoring study of the Egyptian lighthouse of Rethymnon in Crete, Greece. Using structural vibration data collected on a limited number of sensors during a 3-month period, we illustrate the potential of the stretching method for monitoring variations in the natural frequencies of the structure. The stretching method compares two signals, the current that refers to the actual state of the structure, with the reference one that characterizes the structure at a reference healthy condition. For the structure under study, an 8-day time interval is used for the reference quantity while the current quantity is computed using a time window of 24 h. Our results indicate that frequency shifts of 1% can be detected with high accuracy allowing for early damage assessment. We also provide a simple numerical model that is calibrated to match the natural frequencies estimated using the stretching method. The model is used to produce possible damage scenarios that correspond to 1% shift in the first natural frequencies. Although simple in nature, this model seems to deliver a realistic response of the structure. This is shown by comparing the response at the top of the structure to the actual measurement during a small earthquake. This is a preliminary study indicating the potential of the stretching method for structural health monitoring of historical monuments. The results are very promising. Further analysis is necessary requiring the deployment of the instrumentation (possibly with additional instruments) for a longer period of time

L1(0) ordering and magnetic interactions in FePt nanoparticles embedded in MgO and SiO2 shell matrices

FePt nanoparticles have been encapsulated in insulating and protective MgO shells, using a two step chemical process, in order to prevent sintering during the heat-treatment process required for the L1(0) ordering. The FePt nanoparticles were initially prepared using a standard polyol process and then dispersed in a magnesium oxide solution. As a basis for comparison FePt/SiO2 nanocomposites have been also synthesized using a modified aqueous sol-gel route as the second step. The magnetic and microstructural properties of FePt/MgO and FePt/SiO2 nanocomposites are compared with those of FePt nanoparticles. The presence of oxide matrices leads to more homogeneous microstructures and better magnetic properties. While higher coercivity values have been obtained in FePt/SiO2, the MgO matrix is proven to provide better physical and magnetic isolations of the FePt nanoparticles. However, for FePt:MgO molar ratios exceeding 1:20 no L1(0) ordering has been achieved

Flow modeling in Pelton turbines by an accurate Eulerian and a fast Lagrangian evaluation method

The recent development of Computational Fluids Dynamics (CFD) has allowed the flow modeling in impulse hydro turbines that includes complex phenomena like free surface flow, multi fluid interaction, and unsteady, time dependent flow. Some commercial and open-source CFD codes, which implement Eulerian solving methods, have been validated against experimental results showing satisfactory accuracy. Nevertheless, further improvement of the flow analysis accuracy is still a challenge, while the computational cost is very high and unaffordable for multi-parametric design optimization of the turbine’s runner. In the present work, a CFD Eulerian approach is applied at first, in order to simulate the flow in the runner of a Pelton turbine model installed at the laboratory. Then, a particulate method, the Fast Lagrangian Simulation (FLS), is used for the same case, which is much faster than the Eulerian approach, and hence potentially suitable for numerical design optimization, providing that it can achieve adequate accuracy. The results of both methods for various operation conditions of the turbine, as also for modified runner and bucket designs, are presented and discussed in the paper. In all examined cases the FLS method shows very good accuracy in predicting the hydraulic efficiency of the runner, although the computed flow evolution and torque curve during the jet-runner interaction exhibit some systematic differences from the Eulerian results

Compound and acutely ruptured false aneurysm of the brachial artery: a case report

<p>Abstract</p> <p>Introduction</p> <p>A patient with a neglected, compound acutely ruptured false aneurysm of the brachial artery which developed after a periprosthetic fracture of the right humerus, is reported.</p> <p>Case presentation</p> <p>An 84-year-old Greek woman underwent right shoulder hemiarthroplasty 2 years before a periprosthetic fracture which was treated conservatively in another hospital. After removing the U-slab herself, she noticed the development of an ulcer on the mid-humerus, with continuous oozing but no fever. This led to above-elbow amputation in an attempt to save the patient's life.</p> <p>Conclusion</p> <p>It is hoped that by awareness of such a possibility coupled with an early diagnosis based on the clinical picture and imaging modalities, such unfortunate results can be avoided in the future. In case of increasing displacement at the fracture site and excessive local swelling, the possibility of the presence of a false brachial aneurysm should be ruled out despite the presence of normal perfusion of the hand and palpable radial and ulnar pulses.</p

Aortic Isthmus Pseudoaneurysm After Coarctation Repair as a Source of Thromboembolism

A 60 year old male, smoker with a past medical history of moderate hypertension, hypercholesterolemia, bronchial asthma and surgically corrected aortic coarctation with interposition grafting at the age of 17, was presented with four episodes of post-exercise lower limb thromboembolism within a period of two years. The electrocardiogram was normal and multiple Holter recordings showed no rhythm abnormalities. The cardiac transthoracic echocardiogram showed normal left ventricular dimensions and systolic function, normal right ventricle, bicuspid aortic valve with moderate insufficiency and mild stenosis, ascending aorta with a diameter of 46mm, and a pressure gradient across the aortic isthmus of 20mmHg. The cardiac transesophageal echocardiogram revealed no intracardiac thrombi or shunts and in addition neither dissection nor thrombus in the descending thoracic aorta was detected. Although the patient was subjected to multiple diagnostic imaging examinations, it was the Dual Source Computed Tomography with three-dimensional image reconstruction of the aorta that disclosed the detachment of the graft’s wall inner surface at the site of its proximal anastomosis with the descending thoracic aorta, just distal to the origin of the left subclavian artery, that resulted in the formation of a pseudoaneurysm which served as the source of distally embolizing thrombi. Moreover, in the distal thoracic aorta just after the graft’s distal anastomosis, a mild stenosis occurred due to intense intramural calcification. Although various therapeutic approaches were considered, the patient was finally taken to the operating theatre, where, via a left lateral thoracotomy, the preoperative findings were confirmed and the lesions successfully repaired

Mid-term outcomes in the treatment of retroperitoneal sarcomas: a 12-year single-institution experience

Aim To present the experience from collective data regarding patients with retroperitoneal sarcomas that have been operated in and followed up by the University General Hospital of Patras in Rion, Greece, between 2009 and 2020. Methods A retrospective analysis of adult patients treated at our hospital with a diagnosis of primary retroperitoneal sarcoma who underwent tumour resection. Results Data from 29 patients were analysed. The mean age at diagnosis was 56.1 years; 55.2% of patients were male (n=16). Liposarcomas (on histology) were identified in 19 (65.5%) patients, leiomyosarcoma six (20.7%), and other histologic subtypes in four (13.8%) patients. Tumours >5cm were presented in 27 (93.1%) patients. Negative margins were attained in 13 (44.8%) of all patients who underwent surgical resection. Five (17.2%) patients received neoadjuvant radiation, four (13.8%) postoperative radiation, and three (10.3%) patients received both chemotherapy and radiation prior to surgery with the rest of the patients being treated with surgical excision alone. A 3-year follow-up was successful in 21 (72.4%) patients; five (23.8%) patients died. In total, 16 (55.2%) patients were found to have a local recurrence, with no significant difference in patients' age, gender, tumour size, histology, negative surgical margin (Ro) resection, neoadjuvant chemotherapy, or radiation therapy. There was a significant difference in the 3-year survival rate between patients having positive or negative surgical margins (p=0.027). Conclusion The higher 3-year survival rate in patients with retroperitoneal sarcomas when achieving Ro resection warrant further investigation with a larger sample size across different institutions