Decomposing the High School Timetable Problem

The process of timetable construction is a common and repetitive task for High Schools worldwide. In this paper a generic approach is presented for Greek High Schools organized around the idea of solving a significant number of tractable Integer Programming problems. Variables of the underlying mathematical model correspond to daily teacher schedules while a number of hard and soft constraints are included so as for the model to handle practical aspects that manifest themselves in Greek High Schools. By selecting better teacher schedules that exist in subproblems the quality of the overall solution gradually improves. The collected results which are obtained within reasonable time are most promising. The strength of the approach is supported by the fact that it managed to find the best known results for two public instance problems included in the Benchmarking Project for High School Timetabling (XHSTT-2012 1 )

Perspective Chapter: Moderate Aortic Stenosis and Heart Failure With Reduced Ejection Fraction; Early Replacement or Conservative Treatment?

Aortic stenosis (AS) is the most common valve lesion among the continuously aging population with serious effect on the left ventricular ejection fraction (LVEF). If left untreated, it is associated with serious complications such as heart failure (HF), pulmonary hypertension, thromboembolic events, and even sudden death. Early diagnosis and treatment is of outmost importance to avoid the above complications but also to maintain the patient’s normal heart function. Echocardiography is the key examination that assesses the severity of the stenosis, valve calcification, left ventricular (LV) function, and wall thickness. Also new imaging methods such as cardiac computed tomography (CT) and cardiac magnetic resonance imaging (MRI) help in assessing the severity of aortic valve stenosis when echocardiography has limitations. Based on the categorization of the severity of the stenosis, its treatment is determined. Although things are clear in cases of asymptomatic disease and severe stenosis, this is not the case in moderate disease. Experts and clinical trials do not define clearly which cases can be treated conservatively and which need surgical or transcatheter intervention. The purpose of this article is to gather all the latest data on the treatment of moderate aortic stenosis, especially in patients with heart failure and low ejection fraction

Near-unity broadband omnidirectional emissivity via femtosecond laser surface processing

It is very challenging to achieve near perfect absorption/emission that is both broadband and omnidirectional while utilizing a scalable fabrication process. Femtosecond laser surface processing is an emerging low-cost and large-scale manufacturing technique used to directly and permanently modify the surface properties of a material. The versatility of this technique to produce tailored surface properties has resulted in a rapidly growing number of applications. Here, we demonstrate near perfect, broadband, omnidirectional emissivity from aluminum surfaces by tuning the laser surface processing parameters including fluence, pulse count, and the ambient gas. Full-wave simulations and experimental results prove that the obtained increase in emissivity is mainly a result of two distinct features produced by femtosecond laser surface processing: the introduction of microscale surface features and the thick oxide layer. This technique leads to functionalized metallic surfaces that are ideal for emerging applications, such as passive radiative cooling and thermal management of spacecraft

TREM-1 expression on neutrophils and monocytes of septic patients: relation to the underlying infection and the implicated pathogen

<p>Abstract</p> <p>Background</p> <p>Current knowledge on the exact ligand causing expression of TREM-1 on neutrophils and monocytes is limited. The present study aimed at the role of underlying infection and of the causative pathogen in the expression of TREM-1 in sepsis.</p> <p>Methods</p> <p>Peripheral venous blood was sampled from 125 patients with sepsis and 88 with severe sepsis/septic shock. The causative pathogen was isolated in 91 patients. Patients were suffering from acute pyelonephritis, community-acquired pneumonia (CAP), intra-abdominal infections (IAIs), primary bacteremia and ventilator-associated pneumonia or hospital-acquired pneumonia (VAP/HAP). Blood monocytes and neutrophils were isolated. Flow cytometry was used to estimate the TREM-1 expression from septic patients.</p> <p>Results</p> <p>Within patients bearing intrabdominal infections, expression of TREM-1 was significantly lower on neutrophils and on monocytes at severe sepsis/shock than at sepsis. That was also the case for severe sepsis/shock developed in the field of VAP/HAP. Among patients who suffered infections by Gram-negative community-acquired pathogens or among patients who suffered polymicrobial infections, expression of TREM-1 on monocytes was significantly lower at the stage of severe sepsis/shock than at the stage of sepsis.</p> <p>Conclusions</p> <p>Decrease of the expression of TREM-1 on the membrane of monocytes and neutrophils upon transition from sepsis to severe sepsis/septic shock depends on the underlying type of infection and the causative pathogen.</p

Solving the Distributed Permutation Flow-Shop Scheduling Problem Using Constrained Programming

The permutation flow-shop scheduling problem is a classical problem in scheduling that aims at identifying the optimal sequence of jobs that should be processed in a number of machines in an effort to minimize makespan or some other performance criterion. The distributed permutation flow-shop scheduling problem adds multiple factories where copies of the machines exist and asks for minimizing the makespan on the longest-running location. In this paper, the problem is approached using Constraint Programming and its specialized scheduling features, such as interval variables and non-overlap constraints, while a novel heuristic is proposed for computing lower bounds. Two constraint programming models are proposed: one that solves the Distributed Permutation Flow-shop Scheduling problem, and another one that drops the constraint of processing jobs under the same order for all machines of each factory. The experiments use an extended public dataset of problem instances to validate the approach’s effectiveness. In the process, optimality is proved for many problem instances known in the literature but has yet to be proven optimal. Moreover, a high speed of reaching optimal solutions is achieved for many problems, even with moderate big sizes (e.g., seven factories, 20 machines, and 20 jobs). The critical role that the number of jobs plays in the complexity of the problem is identified and discussed. In conclusion, this paper demonstrates the great benefits of scheduling problems that stem from using state-of-the-art constraint programming solvers and models that capture the problem tightly

Η επίπτωση των κολπικών έκτακτων συστολών σε ασθενείς με κρυπτογενές αγγειακό εγκεφαλικό επεισόδιο και η εμφάνιση κολπικής μαρμαρυγής κατά τη διάρκεια παρακολούθησης

Εισαγωγή: Η κολπική μαρμαρυγή (ΚΜ) αποτελεί μια από τις κύριες αιτίες αγγειακών εγκεφαλικών επεισοδίων (ΑΕΕ). Σκοπός: Η προγνωστική αξία της αυξημένης κολπικής δραστηριότητας (ΑΚΔ) στην μετέπειτα παρουσία κολπικής μαρμαρυγής σε ασθενείς με κρυπτογενές ΑΕΕ. Υλικό και Μέθοδος: Μελετήθηκαν αναδρομικά 124 ασθενείς οι οποίοι νοσηλεύτηκαν τη χρονική περίοδο 2014-2015 ως κρυπτογενές ΑΕΕ. Στο Holter 24ώρου το οποίο είχε τοποθετηθεί κατά τη νοσηλεία τους, καταγράφηκαν οι εκτακτες κολπικές συστολές/ώρα (PACs/h) και τα επεισόδια βραχείας διάρκειας (&lt;30 sec) ριπών κολπικών έκτακτων συστολών. Μετρήθηκε η διάρκεια σε δευτερόλεπτα και εκτιμήθηκε η διάρκεια του μεγαλύτερου επεισοδίου (longest SVR). Ως τελική έκβαση ορίστηκε η εμφάνιση ΚΜ. Αποτελέσματα: Παρακολουθήθηκαν 124 ασθενείς με μέση περίοδο παρακολούθησης 5 έτη, εκ των οποίων οι 35 (28.2%) ήταν γυναίκες. Από το σύνολο των 111 ασθενών που επέζησαν (89,5%), οι 13 (10.5%) εμφάνισαν ΚΜ. Η διάμεση ηλικία ήταν 56 (IQR = 49 – 61.75) έτη και διέφερε μεταξύ των ασθενών με ΚΜ (ομάδα AF) και χωρίς ΚΜ (ομάδα non-AF), (60 vs. 54 έτη, αντίστοιχα, p=0.01). Τα υπόλοιπα χαρακτηριστικά (κάπνισμα, σακχαρώδης διαβήτης, δυσλιπιδαιμία και υπέρταση) δεν διέφεραν μεταξύ των δύο ομάδων (p&gt;0.05). Η διάμεση τιμή του CHA2DS2-VASc score ήταν 3 (IQR = 3 – 4), χωρίς να διαφέρει για τις δύο ομάδες (p=0.252). Το σύνολο των ασθενών εμφάνισε 0.42 (IQR = 0.04 – 1.29) PACs/h, ο αριθμός των οποίων διέφερε σημαντικά μεταξύ των ομάδων AF και non-AF (23.96 vs. 0.21, αντίστοιχα, p&lt;0.001). Από σύνολο των ασθενών το (76.6%) δεν είχε καμία SVR, όπως επίσης και από την ομάδα non-AF. Αντίθετα, η ομάδα AF εμφάνισε σημαντικά μεγαλύτερη “longest SVR” (3, IQR=0.75 – 5, p&lt;0.001). Αναδείχθηκε η συσχέτιση μεταξύ “PACs/h” και “longest SVR” (p&lt;0.001). Πολλαπλά μοντέλα λογιστικής παλινδρόμησης έδειξαν την ισχυρή, ανεξάρτητη συσχέτιση της AF με τις μεταβλητές “PACs/h” και “longest SVR” (p≤0.001). Μελέτη ROC ανέδειξε τη σημαντική διαγνωστική αξία των μεταβλητών “PACs/h” και “longest SVR” όσον αφορά στην ΚΜ. Συμπεράσματα: Η ανεύρεση (ΑΚΔ) στο Holter 24ώρου σε ασθενείς με κρυπτογενές ΑΕΕ, αποτελεί έναν ισχυρό προγνωστικό δείκτη μελλοντικής εμφάνισης ΚΜ στην 5ετίαObjective: Atrial fibrillation (AF) is a leading preventable cause of ischemic stroke. The aim of this study was the prognostic role of Excessive supraventricular ectopic activity (ESVEA) in the subsequent presence of atrial fibrillation in patients with cryptogenic stroke. Design and method: We retrospectively evaluated 124 patients who were hospitalized during 2014 and 2015 with cryptogenic stroke. The premature atrial complexes/ hour (PACs/h) and the longest supraventricular run (&lt;30sec) (longest SVR) have been recorded, from the 24-Hour Holter monitoring during their hospitalization. As primary outcome has been defined the presence of subsequent AF. Results: One hundred and twenty-four patients were studied during a mean 5 years follow-up. The median age was 56 (IQR = 49 – 61.75) years and 35 (28,8%) were women. The mean age of AF group was 60 years vs. 54 years in non-AF group (p=0,01). There was no difference between the remaining variables (smoking, diabetes mellitus, dyslipidemia and hypertension) of the two groups (p&gt;0.05). The median value of CHA2DS2-VASc score was 3 (IQR = 3 – 4) and was similar in the two groups (p=0.252). The AF group had significant more number of PACs/h, than the non-AF group (23.96/ h vs. 0.21/ h, p&lt;0.001). No episodes of SVR was recorded in 76,6% of all patients and in all non-AF group patients. In contrast, the AF group had significantly longer “longest SVR” (3 sec. IQR=0.75 – 5, p&lt;0.001). The association between PACs/h and “longest SVR” (p&lt;0.001) has been showed. Different multiple logistic regression models demonstrated the strong independent correlation between AF and the variables “PACs/h” and “longest SVR” (p≤0.001). ROC curve demonstrated the significant diagnostic value of “PACs/h” and “longest SVR” variates regarding AF . Conclusions: The presence of ESVEA measured with 24h-Holter in patients with cryptogenic stroke, is associated with increased risk of AF

Combinatorial optimization algorithms with emphasis on metaheuristic techniques

The main topic of this thesis is the combination of metaheuristics and other methods for solving combinatorial optimization problems (COPs). In particular, focus is given in a special category of COPs known as timetabling problems. Timetabling problems belong in general to the class of NP-hard problems meaning that exact methods are usually unable to solve problem instances with sizes of practical importance. In the first three chapters optimization problems are analyzed and four major disciplines regarding optimization approaches are examined: Mathematical Programming, Artificial Intelligence, Computational Intelligence and Metaheuristics. Borders are not always clear between them while a recent trend is to hybridize approaches originating from the same or different disciplines. Even with the progress in optimization that occurred during the last decades programming successful optimization application still is an intricate mission. Nevertheless, software developing techniques, open source software and exploitation of the processing power of modern hardware can assist in constructing applications that are expected to be of much benefit for their users. Key ideas of achieving this are described in Chapter 4. The first application, presented in Chapter 5, is a pump scheduling system for a water distribution network. The objective is to achieve a way of operation for the pumps of each reservoir that results in diminished electricity cost. A model of the problem was constructed and the metaheuristic technique of genetic algorithms with the addition of several heuristics solved the problem. The second application, presented in Chapter 6, is the examination timetabling problem for Universities. Educational timetabling problems in general attract much interest from the scientific community. Our approach targeted various models of the examination timetabling problem and constituted by two major phases: construction and improvement. A number of metaheuristics were hybridized (Simulated Annealing, GRASP, VNS, Taboo Search and others) while certain sub-problems were solved using exact methods (Integer Programming). The results that we achieved in known datasets for evaluating the performance of such methods were most promising. In particular, for the publicly available datasets of the second International Timetabling Competition our approach achieved the best published score for 6 out of 8 datasets. The third application, presented in Chapter 7, is the construction of timetables for Greek high schools. A model of the problem that had publicly available problem instances and published results was used. Better results were able to be obtained by reformulating the problem and subsequently using a branch and cut approach implemented using entirely open source software. In summary, successful results of our approaches suggest that metaheuristics and hybridized metaheuristics with other metaheuristic or exact methods appears to be a promising research direction for handling complex combinatorial optimization problems

Δίκαιη κατανομή μετοχών στούς πελάτες μιάς χρηματιστηριακής. Μιά εφαρμογή βελτιστοποίησης στην εκκαθάριση.

Abstract We present how a standard task in the clearance of financial brokers can find new creative, integer optimization, computerized solutions. The broker makes wholesome massive transactions of Stock Exchange securities and then wants to distribute them in a fair way to the retail customers, so that each one has almost the same average price of buying or selling