138 research outputs found
Microvessel Density in Patients with Cutaneous Melanoma: An Up-to-Date Systematic Review and Meta-Analysis
No full textBackground. We conducted a meta-analysis, in order to appraise the effect of microvessel density (MVD) on the survival of patients with cutaneous melanoma. Methods. This study was conducted according to the PRISMA guidelines and the Cochrane Handbook for Systematic Reviews of Interventions. A systematic literature search in electronic databases (MEDLINE, Web of Science, and Cochrane Central Register of Controlled Clinical Trials) was performed. Fixed Effects or Random Effects model was used, based on the Cochran Q test. Results. In total 9 studies (903 patients) were included. Pooled HR for overall survival (OS) and disease-free survival (DFS) were 2.62 (95% CI: 0.71-9.60, p=0.15) and 2.64 (95% CI: 0.82-8.47, p=0.10), respectively. Odds ratios of overall survival between high and low MVD groups, at 12 (1.45, 95% CI: 0.16-13.24), 36 (2.93, 95% CI: 0.63-13.59), and 60 (4.09, 95% CI: 0.85-19.77) months did not reach statistical significance. Significant superiority of low MVD group, in terms of DFS, at all time intervals (OR: 4.69, p<0.0001; OR: 2.18, p=0.004; OR: 7.46, p=0.01, resp.) was documented. Discussion. MVD does not affect the HR of OS and DFS. A strong correlation with DFS rates at 12, 36, and 60 months was recorded. © 2017 Konstantinos Perivoliotis et al
Pancreatogastrostomy versus Pancreatojejunostomy: An Up-to-Date Meta-Analysis of RCTs
No full textBackground. A meta-analysis was conducted in order to provide an up-to-date comparison of pancreatogastrostomy (PG) and pancreatojejunostomy (PJ), after pancreatoduodenectomy (PD), in terms of clinically significant postoperative pancreatic fistula (POPF) and other postoperative complications. Methods. This meta-analysis was conducted according to the PRISMA guidelines and the Cochrane Handbook for Systematic Reviews of Interventions. A systematic literature search in MEDLINE and Cochrane Central Register of Controlled Clinical Trials was performed. Fixed Effects or Random Effects model was used, based on the Cochran Q test. Results. In total, 10 studies (1629 patients) were included. There was no statistical significance between PG and PJ regarding the rate of clinically significant POPF (OR: 0.70, 95%CI: 0.46-1.06). PG was associated with a higher rate of postpancreatoduodenectomy haemorrhage (PPH) (OR: 1.52, 95%CI: 1.08-2.14). There was no difference between the two techniques in terms of clinically significant PPH (OR: 1.35, 95%CI: 0.95-1.93) and clinically significant postoperative delayed gastric emptying (DGE) (OR: 0.98, 95%CI: 0.59-1.63). Discussion. There is no difference between the two anastomotic techniques regarding the rate of clinically significant POPF. Given several limitations, more large scale high quality RCTs are required. © 2017 Konstantinos Perivoliotis et al
Toxicity determinants of multi-walled carbon nanotubes: The relationship between functionalization and agglomeration
No full textThe elucidation of toxicity determinants of multi-walled carbon nanotubes (MWCNT) is still incomplete. Functionalization with carboxyl groups is, however, commonly used to mitigate MWCNT toxicity, although the rationale for the mitigating effect has not been fully clarified yet. In this work, two optimized chemical vapor deposition methods were employed to obtain MWCNT of comparable length but different diameter, which were subsequently functionalized. For MWCNT of diameter larger than 40. nm, no detrimental effects on cell viability of macrophages were observed, while mild cytotoxicity was recorded for diameters between 15 and 40. nm, with a mitigating effect of functionalization. To investigate the factors responsible for the mitigation, we used the thinnest MWCNT preparation on different cell models, evaluating several endpoints, such as viability, production of nitric oxide (NO), expression of pro-inflammatory markers, the Trans-Epithelial Electrical Resistance (TEER), and clonogenic activity. Substantial mitigation of the changes caused by pristine MWCNT was observed not only with carboxyl- but also with amino-functionalized MWCNT, suggesting that negative or positive surface charge was not the main factor responsible for the effect. Instead, either functionalized preparation exhibited a stronger tendency to agglomerate that was strictly dependent on the presence of proteins. Moreover, we found that either carboxyl- or amino-functionalized MWCNT adsorbed a larger amount of serum proteins than pristine counterparts, with a distinctive pattern for each type of MWCNT. We propose, therefore, that the formation of larger agglomerates, dependent upon different protein coronae, contributes to mitigate the biological effects of functionalized MWCNT in protein-rich biological media
Oil spill forecasting (prediction)
No full textOil spills in the ocean are a matter of concern due to the damaging effect they can have on coastal and offshore resources. This work presents a review of present-day modeling techniques used in the mitigation of oil spills by booms, skimmers, chemical dispersants, and other equipment and the importance of the controlling parameters of these techniques. Three basic questions need to be addressed by oil spill models: (1) where the spill will move, (2) when will the spill get to the modeled endpoints, and (3) what will be its state when it arrives. The first two questions are relatively urgent, as far as response measures are concerned, and depend closely on the use of accurate data on winds, sea currents, and wave action as oil spill accidents evolve. Obtaining a reasonable answer to the third question lies in the use of reliable fate algorithms. Oil spill models can be divided in two types: Euleurian and Langragian. Adding to information regarding the oil type and its initial location, all oil spill models require data for the wind fields, sea state, sea-surface temperature, and currents, as well as other environmental parameters, if available. Such reliable data suit the needs of oil spill modeling predictions and are available daily at global, regional, and coastal scales within the broader scope of operational oceanography. Advanced oil spill models available at present use satellite synthetic aperture radar (SAR) images/data to detect possible oil slicks and assimilate slick and drifter observations to correct slick predictions. The emphasis of research and governmental institutions has been on improving 4D predictions obtained through simulation of oil spills backward in time to track the slicks back to their source. Such backward simulations, when integrated with ships’ Automatic Identification Systems (AIS), will be used to locate the sources of oil slicks around the world’s oceans and seas. © 2017 George Zodiatis, Robin Lardner, Tiago M. Alves, Yiannis Krestenitis, Leonidas Perivoliotis, Sarantis Sofianos, and Katerina Spanoudaki
Marine SAR Analysis and Interpretation System - MARSAIS
No full textThere is a growing need for better monitoring and managing of the marine coastal zone environment. The parameters and features most frequently required for their relevance and importance include: (a) surface waves and high-resolution wind fields; (b) surface current strength and variability; and (c) identification and location of pollutant material including toxic algae bloom and oil spill. Remote sensing observations play a valuable role in this context. Mature algorithms and synthetic aperture radar (SAR) imaging models are integrated and supplemented by complementary thermal and visible sensor data. This paper outlines how a system like MARSAIS can guide and help non-experts in exploring SAR imaging data for coastal ocean monitoring
Circulation and hydrological characteristics of the North Aegean Sea: a contribution from real-time buoy measurements
No full textIn the framework of the POSEIDON Project, a network of open sea oceanographic buoys equipped with meteorological and oceanographic sensors has been operational in the Aegean Sea since 1998. The analysis of upper-ocean physical data (currents at 3m, temperature and salinity at 3-40m depths) collected during the last 2 years from the stations of the North Aegean basin indicates a strong temporal variability of flow field and hydrological characteristics in both synoptic and seasonal time scales. The northern part of the basin is mainly influenced by the Black Sea Water outflow and the mesoscale variability of the corresponding thermohaline fronts, while the southern stations are influenced by the general circulation of the Aegean Sea with strong modulations caused by the seasonally varying atmospheric forcing
Cecorectal (CRA) versus ileorectal (IRA) anastomosis after colectomy for slow transit constipation (STC): a meta-analysis
No full textIntroduction: We conducted this meta-analysis, to compare cecorectal (CRA) and ileorectal anastomosis (IRA), regarding perioperative safety and efficacy, in patients submitted to colectomy for refractory slow transit constipation (STC). Methods: This study followed the Cochrane Handbook for Systematic Reviews of Interventions and the PRISMA guidelines. To identify all eligible records, a systematic literature search in the electronic scholar databases (Medline, Scopus, Web of Science) was performed. Results: Overall, 5 trials and 291 patients were included in this meta-analysis. Pooled comparisons confirmed the comparability of the two techniques regarding perioperative complications (p = 0.55). CRA was associated with a shorter operation (p = 0.0004) and hospitalization duration (p = 0.001). Although there was no difference in terms of gastrointestinal symptoms, functional outcomes, and patient satisfaction, CRA resulted in lower long-term Wexner scores (p < 0.0001). Conclusion: Due to several study limitations, further large-scale RCTs are required to verify the findings of the present meta-analysis. © 2022, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature
Σύνθεση και χαρακτηρισμός νανοσύνθετων κεραμικών επιστρώσεων οργανικά τροποποιημένων πυριτικών ενώσεων στο κράμα του αλουμινίου 2024-Τ3
No full text128 σ.Στην παρούσα διπλωματική εργασία μελετήθηκε η ανάπτυξη συστημάτων προστασίας του κράματος του αλουμινίου 2024 – Τ3. Το κράμα αυτό είναι από τα πλέον συχνά χρησιμοποιούμενα κράματα στην αεροναυπηγική βιομηχανία λόγω των εξαιρετικών μηχανικών ιδιοτήτων που παρουσιάζει σε συνδυασμό με το χαμηλό του κόστος. Διερευνήθηκε η αντιδιαβρωτική ικανότητα καθώς και οι μηχανικές ιδιότητες ενός sol gel συστήματος προστασίας βασιζόμενο 3-γλυσιδοξυ-προπυλ-τριμεθοξυ-σιλάνιο (GPTMS) που περιέχει κεραμικά νανοδοχεία οξειδίου του δημητρίου/μολυβδαινίου (CeMo) πληρωμένα με τον αναστολέα διάβρωσης 2 – μερκαπτοβενζοθιαζόλη (2-MBT). Για λόγους σύγκρισης μελετήθηκε επιπλέον το σύστημα της επίστρωσης το οποίο όμως περιείχε άδεια νανοδοχεία CeMo καθώς και το σύστημα που δεν περιείχε ούτε νανοδοχεία ούτε αναστολέα. Όλες οι επιστρώσεις εναποτέθηκαν με την τεχνική της εμβάπτισης (dip coating). Οι αντιδιαβρωτικές ιδιότητες των επιστρώσεων μελετήθηκαν αρχικά ως συνάρτηση της θερμοκρασίας ξήρανσης. Η έκταση της αντιδιαβρωτικής προστασίας των συντεθειμένων επιστρώσεων εξετάστηκε ηλεκτροχημικά χρησιμοποιώντας EIS. Στα ίδια δείγματα, η σύσταση και η δομή μελετήθηκαν με FT-IR, EDX και SEM. Οι νανομηχανικές και νανοτριβολογικές ιδιότητες όλων των επιστρώσεων διερευνήθηκαν με νανοσκληρομέρηση. Τα πειράματα που πραγματοποιήθηκαν έδειξαν ότι η καταλληλότερη θερμοκρασία γήρανσης ήταν 100ο C για 36 ώρες παραμονής στον φούρνο. Επιπλέον, αποδείχθηκε ότι η επίστρωση με τα πληρωμένα με αναστολέα νανοδοχεία παρείχε την καλύτερη αντιδιαβρωτική προστασία ενώ η επίστρωση με τα άδεια νανοδοχεία παρουσίασε την χειρότερη αντιδιαβρωτική συμπεριφορά. Τέλος, διερευνήθηκε η ικανότητα μερικής αποκατάστασης (partial recovery) της επίστρωσης με τα πληρωμένα νανοδοχεία η οποία υποδηλώνει φαινόμενα αυτοΐασης (self-healing). Αυτή η νέα τεχνολογία παρουσιάζει ένα δυνητικό υποψήφιο για την αντικατάσταση των χρωμικών επικαλύψεων που χρησιμοποιούνται σήμερα καθώς το χρώμιο δεν είναι φιλικό προς το περιβάλλον ενώ παράλληλα προκαλεί καρκινογένεσεις στον ανθρώπινο οργανισμό και η χρήση του έχει απαγορευτεί.The thesis presented investigates the development of inorganic-organic hybrid coatings by sol-gel process, aiming at the corrosion protection of aluminum alloy 2024-T3. Due to its excellent mechanical properties and low cost, this alloy has been widely used in advanced applications of the aerospace industry. The present work aims at producing and assessing the corrosion protection conferred to the aluminium alloy 2024-T3 by hybrid sol gel films based on 3-glycidoxypropyltrimethoxy silane (GPTMS) which includes CeMo nanocontainers loaded with the anodic corrosion inhibitor 2-mercaptobenzothiazole (2-MBT). Furthermore, for comparison, the anticorrosion properties of coatings of the same composition with empty nanocontainers as well as the coatings without nanocontainers were investigated. All coatings were deposited via the dip-coating process. Extent of the anti-corrosion protection of the formed coatings was examined electrochemically using EIS. In the same samples, the composition and structure were investigated by FT-IR, EDX and SEM. The anti-corrosion properties of the coatings were investigated as a function of the temperature. Also, the nanomechanical properties of the coatings were also examined via nanoindentation technique. The results showed that the most suited drying was 100 οC for 36 hours. Additionally, we demonstrated that coating with ceramic nanocontainers loaded with inhibitor performs better than the other coatings. Finally, artificial defects were made onto the coating which includes CeMo nanocontainers loaded with corrosion inhibitor 2-MBT in order for the possible self-healing properties to be estimated. This new technology presents a potential candidate for substitution of the chromate pretreatmens, since hexavalent chromium is carcinogenic and has been forbidden from corrosion protection applications.Δημήτριος Κ. Περιβολιώτη
Synthesis of carbon nanotubes via chemical vapor deposition method for advanced applications
No full text86 σ.Εθνικό Μετσόβιο Πολυτεχνείο--Μεταπτυχιακή Εργασία. Διεπιστημονικό-Διατμηματικό Πρόγραμμα Μεταπτυχιακών Σπουδών (Δ.Π.Μ.Σ.) “Επιστήμη και Τεχνολογία Υλικών”Οι νανοσωλήνες άνθρακα (CNTs) βρίσκουν πληθώρα προηγμένων εφαρμογών, λόγω των εξαιρετικών δομικών, ηλεκτρικών και μηχανικών ιδιοτήτων τους. Ο κύριος στόχος της συγκεκριμένης μεταπτυχιακής εργασίας είναι η σύνθεση νανοσωλήνων άνθρακα μέσω χημικής απόθεσης ατμών για προηγμένες εφαρμογές. Η παρούσα εργασία αποτελείται από τρία κύρια μέρη.
Το πρώτο μέρος ασχολείται με την σύνθεση νανοσωλήνων άνθρακα μέσω χημικής απόθεσης ατμών, χρησιμοποιώντας καμφορά (C10H16O) ως πηγή άνθρακα και φερροκένιο ως καταλύτη. Μελετήθηκε η επίδραση της θερμοκρασίας ανάπτυξης καθώς και της ροής του φέροντος αερίου στην ποιότητα του ανθρακούχου υλικού που αποτέθηκε. Ηλεκτρονική μικροσκοπία σάρωσης (SEM), περίθλαση ακτινών Χ (XRD), θερμοσταθμική ανάλυση (TGA) και φασματοσκοπία Raman χρησιμοποιήθηκαν με σκοπό να διερευνηθούν οι βέλτιστες συνθήκες για την ανάπτυξη των CNTs. Στα πλαίσια των συγκεκριμένων πειραματικών συνθηκών που μελετήθηκαν, παραγωγή CNTs (διάμετρος ~60nm) επιτεύχθηκε για θερμοκρασία ανάπτυξης 800o C, ροή φέροντος αερίου 330 ml/min και αναλογία καμφοράς/φερροκένιου ίση με 20:1. Οι CNTs που παρήχθησαν παρουσίασαν μικρότερο βαθμό κρυσταλλικότητας σε σύγκριση με δείγμα εμπορικών CNTs.
Το δεύτερο μέρος ασχολείται με την μελέτη της μικροδομής και των μηχανικών ιδιοτήτων συγκολλημένων δια τριβής μέσω ανάδευσης (FSW) ανόμοιων κραμάτων του αλουμινίου (AA5083-H111 και AA6082-T6) χρησιμοποιώντας νανοσωλήνες άνθρακα (CNTs) ως μέσο ενίσχυσης, με την τεχνική της νανοδιείσδυσης. Η διασπορά των CNTs στην μήτρα ήταν σχεδόν ομοιόμορφη. Η μέση τιμή της κατανομής του μέτρου ελαστικότητας ήταν κοντά σε αυτή των μετάλλων βάσης. Στην ζώνη ανάδευσης, παρατηρήθηκαν αυξημένες κατά ~10% τιμές σκληρότητας λόγω της παρουσίας του μέσου ενίσχυσης.
Το τρίτο μέρος ασχολείται με την μελέτη των νανομηχανικών ιδιοτήτων πολυστρωματικών υβριδικών νανοσυνθέτων υλικών. Πειράματα νανοδιείσδυσης πραγματοποιήθηκαν σε διαφορετικούς τύπους πολυστρωματικών νανοσυνθέτων και τα αποτελέσματα έδειξαν ότι η μηχανική απόκριση του συνθέτου εξαρτάται από την φύση των εσωτερικών στρωμάτων. Συγκεκριμένα, το TNTs (primer layer)–Epoxy–CNTs (external layer) νανοσύνθετο παρουσίασε βελτιωμένες μηχανικές ιδιότητες συγκρινόμενο με τους άλλους συνδυασμούς και μπορεί να θεωρηθεί η πιο λειτουργική δομή.Carbon nanotubes (CNTs) have received a great deal of attention due to their various advanced potential applications, deriving from their extraordinary structural, electronic and mechanical properties. The main objective of this thesis is the synthesis of carbon nanotubes (CNTs) via chemical deposition (CVD) method for advanced applications. This thesis consists of three main parts.
In the first part, CNTs were synthesized via chemical vapor deposition using camphor (C10H16O) as carbon source and ferrocene as catalyst compound. The influence of growth temperature and carrier gas (N2) flow on quality of carbonaceous material deposited was studied. Scanning Electron Microscopy (SEM), X-Ray analysis (XRD), Thermogravimetric analysis (TGA) and Raman spectroscopy are used in order to investigate the optimum conditions for the CNTs growth. Under the present experimental conditions, production of CNTs (mean external diameter ~60nm) was obtained at 800o C growth temperature, 330 ml/min carrier gas flow and 20:1 camphor/ferrocene mass ratio. The synthesized CNTs exhibit lower crystallinity and purity compared with the reference sample of commercial CNTs.
In the second part the microstructural and mechanical properties of dissimilar friction stir butt welds of AA5083-H111 and AA6082-T6 plates using CNTs as reinforcements were investigated, through nano- indentation technique. The distribution of CNTs in the weld region was quasi-homogeneous. The mean average young’s modulus distribution was near to this of the parent materials. However, the stir zone exhibit 10% higher nano-hardness values than the AA5083-H111 parent material, due to the CNTs addition.
In the third part, the aim was the investigation of nanomechanical properties of multilayered hybrid nanocomposites. Nanoindentation tests were performed on the different multilayered types of nanocomposites and the results showed that the measured properties depended on the type of the underlying substrates. The TNTs (primer layer)–Epoxy–CNTs (external layer) nanocomposite presented improved mechanical properties in comparison to all other combinations and it can be considered the most efficient structure.Δημήτριος Κ. Περιβολιώτη
The role of percutaneous tibial nerve stimulation (PTNS) in the treatment of chronic anal fissure: a systematic review
No full textPurpose: This study was designed to summarize the current evidence regarding the role of percutaneous tibial nerve stimulation (PTNS) in the treatment of chronic anal fissure (CAF). Methods: The present systematic review of the literature was conducted on the basis of the PRISMA guidelines and the Cochrane Handbook for Systematic Reviews of Interventions. The primary endpoint of our study was the CAF recurrence rate. Quality assessment was based on the RoB 2 tool and the Case Series Quality Checklist. Results: Overall, 5 studies and 102 patients were included. A considerably heterogeneity in the neuromodulation technique and setting was identified. The pooled recurrence rate was estimated at the level of 19% (16/84). Post-interventional pain and Wexner scores were considerably reduced. The 2-month healing rate was 72% (18/25), whereas 73.6% of patients were symptom-free at 6 months. Conclusions: PTNS is an effective alternative for the non-operative management of CAF. Due to several limitations further larger and higher quality studies are required. © 2021, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature
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