Latent Gaussian Count Time Series Modeling

This paper develops theory and methods for the copula modeling of stationary count time series. The techniques use a latent Gaussian process and a distributional transformation to construct stationary series with very flexible correlation features that can have any pre-specified marginal distribution, including the classical Poisson, generalized Poisson, negative binomial, and binomial count structures. A Gaussian pseudo-likelihood estimation paradigm, based only on the mean and autocovariance function of the count series, is developed via some new Hermite expansions. Particle filtering methods are studied to approximate the true likelihood of the count series. Here, connections to hidden Markov models and other copula likelihood approximations are made. The efficacy of the approach is demonstrated and the methods are used to analyze a count series containing the annual number of no-hitter baseball games pitched in major league baseball since 1893

Studies in Multidimensional Stochastic Processes: Multivariate Long-Range Dependence and Synthesis of Gaussian Random Fields

This thesis is concerned with the study of multidimensional stochastic processes with special dependence structures. It is comprised of 3 parts. The first two parts concern multivariate long-range dependent time series. These are stationary multivariate time series exhibiting long-range dependence in the sense that the impact of past values of the series to the future ones dies out slowly with the increasing lag. In contrast to the univariate case, where long-range dependent time series are well understood and applied across a number of research areas such as Economics, Finance, Computer Networks, Physics, Climate Sciences and many others, the study of multivariate long-range dependent time series has not matured yet. This thesis sets proper theoretical foundations of such series and examines their statistical inference under novel models. The third part of the thesis is concerned with two-dimensional stationary Gaussian random fields. In particular, a fast algorithm is proposed for exact synthesis of such fields based on convex optimization and is shown to outperform existing approaches.Doctor of Philosoph

Correction to: Two years later: Is the SARS-CoV-2 pandemic still having an impact on emergency surgery? An international cross-sectional survey among WSES members

Background: The SARS-CoV-2 pandemic is still ongoing and a major challenge for health care services worldwide. In the first WSES COVID-19 emergency surgery survey, a strong negative impact on emergency surgery (ES) had been described already early in the pandemic situation. However, the knowledge is limited about current effects of the pandemic on patient flow through emergency rooms, daily routine and decision making in ES as well as their changes over time during the last two pandemic years. This second WSES COVID-19 emergency surgery survey investigates the impact of the SARS-CoV-2 pandemic on ES during the course of the pandemic. Methods: A web survey had been distributed to medical specialists in ES during a four-week period from January 2022, investigating the impact of the pandemic on patients and septic diseases both requiring ES, structural problems due to the pandemic and time-to-intervention in ES routine. Results: 367 collaborators from 59 countries responded to the survey. The majority indicated that the pandemic still significantly impacts on treatment and outcome of surgical emergency patients (83.1% and 78.5%, respectively). As reasons, the collaborators reported decreased case load in ES (44.7%), but patients presenting with more prolonged and severe diseases, especially concerning perforated appendicitis (62.1%) and diverticulitis (57.5%). Otherwise, approximately 50% of the participants still observe a delay in time-to-intervention in ES compared with the situation before the pandemic. Relevant causes leading to enlarged time-to-intervention in ES during the pandemic are persistent problems with in-hospital logistics, lacks in medical staff as well as operating room and intensive care capacities during the pandemic. This leads not only to the need for triage or transferring of ES patients to other hospitals, reported by 64.0% and 48.8% of the collaborators, respectively, but also to paradigm shifts in treatment modalities to non-operative approaches reported by 67.3% of the participants, especially in uncomplicated appendicitis, cholecystitis and multiple-recurrent diverticulitis. Conclusions: The SARS-CoV-2 pandemic still significantly impacts on care and outcome of patients in ES. Well-known problems with in-hospital logistics are not sufficiently resolved by now; however, medical staff shortages and reduced capacities have been dramatically aggravated over last two pandemic years

Μελέτες στις πολυδιάστατες στοχαστικές διαδικασίες: πολυμεταβλητή εξάρτηση μακράς διάρκειας και σύνθεση τυχαίων πεδίων Gauss

This thesis is concerned with the study of multidimensional stochastic processes with special dependence structures. It is comprised of 3 parts. The first two parts concern multivariate long-range dependent time series. These are stationary multivariate time series exhibiting long-range dependence in the sense that the impact of past values of the series to the future ones dies out slowly with the increasing lag. In contrast to the univariate case, where long-range dependent time series are well understood and applied across a number of research areas such as Economics, Finance, Computer Networks, Physics, Climate Sciences and many others, the study of multivariate long-range dependent time series has not matured yet. This thesis sets proper theoretical foundations of such series and examines their statistical inference under novel models. The third part of the thesis is concerned with two-dimensional stationary Gaussian random fields. In particular, a fast algorithm is proposed for exact synthesis of such fields based on convex optimization and is shown to outperform existing approaches.Η παρούσα διατριβή ασχολείται με τη μελέτη πολυδιάστατων στοχαστικών διαδικασιών που διέπονται από ειδικές σχέσεις εξάρτησης. Η διατριβή αποτελείται από 3 μέρη. Τα δύο πρώτα αφορούν πολυμεταβλητές χρονοσειρές μακράς εξάρτησης. Πρόκειται για στάσιμες πολυμεταβλητές χρονοσειρές που έχουν μακρά «μνήμη», με την έννοια ότι η επίδραση των παρελθοντικές τιμών της σειράς στις μελλοντικές τιμές, μειώνεται με αργό ρυθμό καθώς αυξάνεται η υστέρηση μεταξύ τους. Σε αντίθεση με το μονομεταβλητή περίπτωση, όπου οι χρονοσειρές μακράς εξάρτησης έχουν κατανοηθεί επαρκώς και εφαρμόζονται σε ποικίλες ερευνητικές περιοχές όπως Οικονομικά, Χρηματοοικονομικά, Δίκτυα Υπολογιστών, Φυσική, Κλιματικές Επιστήμες και πολλές άλλες, η μελέτη των πολυμεταβλητών χρονοσειρών μακράς εξάρτησης δεν έχει ωριμάσει πλήρως. Η παρούσα διατριβή θέτει τα κατάλληλα θεωρητικά θεμέλια για τη μελέτη τέτοιων χρονοσειρών, και εξετάζει τη στατιστική συμπερασματολογία τους κάτω από καινοφανή μοντέλα. Το τρίτο μέρος της διατριβής αφορά δισδιάστατα στάσιμα τυχαία πεδία Gauss. Πιο συγκεκριμένα, προτείνεται ένας γρήγορος αλγόριθμος για την ακριβή σύνθεση τέτοιων πεδίων μέσα από μεθόδους κυρτή βελτιστοποίησης και αναδεικνύεται η ανωτερότητα του σε σύγκριση με υφιστάμενες προσεγγίσεις

Affordable Biocidal Ultraviolet Cured Cuprous Oxide Filled Vat Photopolymerization Resin Nanocomposites with Enhanced Mechanical Properties

In this study, Cuprous Oxide (Cu2O), known for its mechanism against bacteria, was used as filler to induce biocidal properties on a common commercial resin stereolithography (SLA) 3D printing resin. The aim was to develop nanocomposites suitable for the SLA process with a low-cost process that mimic host defense peptides (HDPs). Such materials have a huge economic and societal influence on the global technological war on illness and exploiting 3D printing characteristics is an additional asset for these materials. Their mechanical performance was also investigated with tensile, flexural, Charpy’s impact, and Vickers microhardness tests. Morphological analysis was performed through scanning electron microscopy (SEM), atomic force microscopy (AFM), and energy-dispersive X-ray spectroscopy (EDS) analysis, while the thermal behavior was studied through Thermogravimetric Analysis (TGA). The antibacterial activity of the fabricated nanocomposites was investigated using a screening agar well diffusion method, for a gram-negative and a gram-positive bacterium. Three-dimensional printed nanocomposites exhibited antibacterial performance in all loadings studied, while their mechanical enhancement was approximately 20% even at low filler loadings, revealing a multi-functional performance and a potential of Cuprous Oxide implementation in SLA resin matrices for engineering and medical applications

Two years later: Is the SARS-CoV-2 pandemic still having an impact on emergency surgery? An international cross-sectional survey among WSES members

Background The SARS-CoV-2 pandemic is still ongoing and a major challenge for health care services worldwide. In the first WSES COVID-19 emergency surgery survey , a strong negative impact on emergency surgery (ES) had been described already early in the pandemic situation. However, the knowledge is limited about current effects of the pandemic on patient flow through emergency rooms, daily routine and decision making in ES as well as their changes over time during the last two pandemic years. This second WSES COVID-19 emergency surgery survey investigates the impact of the SARS-CoV-2 pandemic on ES during the course of the pandemic. Methods A web survey had been distributed to medical specialists in ES during a four-week period from January 2022, investigating the impact of the pandemic on patients and septic diseases both requiring ES, structural problems due to the pandemic and time-to-intervention in ES routine. Results 367 collaborators from 59 countries responded to the survey. The majority indicated that the pandemic still significantly impacts on treatment and outcome of surgical emergency patients (83.1% and 78.5%, respectively). As reasons, the collaborators reported decreased case load in ES (44.7%), but patients presenting with more prolonged and severe diseases, especially concerning perforated appendicitis (62.1%) and diverticulitis (57.5%). Otherwise, approximately 50% of the participants still observe a delay in time-to-intervention in ES compared with the situation before the pandemic. Relevant causes leading to enlarged time-to-intervention in ES during the pandemic are persistent problems with in-hospital logistics, lacks in medical staff as well as operating room and intensive care capacities during the pandemic. This leads not only to the need for triage or transferring of ES patients to other hospitals, reported by 64.0% and 48.8% of the collaborators, respectively, but also to paradigm shifts in treatment modalities to non-operative approaches reported by 67.3% of the participants, especially in uncomplicated appendicitis, cholecystitis and multiple-recurrent diverticulitis. Conclusions The SARS-CoV-2 pandemic still significantly impacts on care and outcome of patients in ES. Well-known problems with in-hospital logistics are not sufficiently resolved by now; however, medical staff shortages and reduced capacities have been dramatically aggravated over last two pandemic years

Evaluation of a quality improvement intervention to reduce anastomotic leak following right colectomy (EAGLE): pragmatic, batched stepped-wedge, cluster-randomized trial in 64 countries

Background Anastomotic leak affects 8 per cent of patients after right colectomy with a 10-fold increased risk of postoperative death. The EAGLE study aimed to develop and test whether an international, standardized quality improvement intervention could reduce anastomotic leaks. Methods The internationally intended protocol, iteratively co-developed by a multistage Delphi process, comprised an online educational module introducing risk stratification, an intraoperative checklist, and harmonized surgical techniques. Clusters (hospital teams) were randomized to one of three arms with varied sequences of intervention/data collection by a derived stepped-wedge batch design (at least 18 hospital teams per batch). Patients were blinded to the study allocation. Low- and middle-income country enrolment was encouraged. The primary outcome (assessed by intention to treat) was anastomotic leak rate, and subgroup analyses by module completion (at least 80 per cent of surgeons, high engagement; less than 50 per cent, low engagement) were preplanned. Results A total 355 hospital teams registered, with 332 from 64 countries (39.2 per cent low and middle income) included in the final analysis. The online modules were completed by half of the surgeons (2143 of 4411). The primary analysis included 3039 of the 3268 patients recruited (206 patients had no anastomosis and 23 were lost to follow-up), with anastomotic leaks arising before and after the intervention in 10.1 and 9.6 per cent respectively (adjusted OR 0.87, 95 per cent c.i. 0.59 to 1.30; P = 0.498). The proportion of surgeons completing the educational modules was an influence: the leak rate decreased from 12.2 per cent (61 of 500) before intervention to 5.1 per cent (24 of 473) after intervention in high-engagement centres (adjusted OR 0.36, 0.20 to 0.64; P < 0.001), but this was not observed in low-engagement hospitals (8.3 per cent (59 of 714) and 13.8 per cent (61 of 443) respectively; adjusted OR 2.09, 1.31 to 3.31). Conclusion Completion of globally available digital training by engaged teams can alter anastomotic leak rates. Registration number: NCT04270721 (http://www.clinicaltrials.gov)