Ανάπτυξη φωτονικού βιοαισθητήρα με την τεχνική LIFT

Εθνικό Μετσόβιο Πολυτεχνείο--Μεταπτυχιακή Εργασία. Διεπιστημονικό-Διατμηματικό Πρόγραμμα Μεταπτυχιακών Σπουδών (Δ.Π.Μ.Σ.) “Μικροσυστήματα και Νανοδιατάξεις

Διατάξεις εγκλωβισμού και διασποράς του φωτός σε μικρό-δομημένες οπτικές ίνες

Whispering gallery mode (WGMs) resonances are useful for various applications due to their unique characteristics, such as high Q-factor and sensitivity to changes in refractive index. This thesis explores the potential of utilizing whispering gallery mode resonances to study amorphous materials such as ion-rich glass and silk fibroin protein and to correlate the behavior of the spectral resonances with their specific optical and mechanical properties.Whispering gallery mode resonances in thermally polarized glass hetero-fibers with radial symmetry are studied for the first time. In comparison to the spectral behavior of the fibers in their pristine state, the TE and TM polarized responses go through a spectral "cleaning" process; higher-order radial modes are suppressed or eliminated because of radially oriented thermal poling. The thermally poled hetero-fiber WGM cavities have been rigorously simulated utilizing the finite element method. The calculated modal eigenstates and transmission spectra have affirmed the mode selection mechanism introduced by the azimuthally symmetric thermal polling procedure. To reveal the spatial profile of the structural and optical changes introduced to the thermally poled hetero-fibers and correlate them with the WGM spectral measurements, second-harmonic generation (SHG) microscopy, energy dispersive x-ray spectroscopy (EDX), and micro-Raman (μRaman) measurements were carried out.During this research, cylindrical resonators made of silk fibroin were developed and attached to silica glass microfibers. For modal excitation, we employ a technique known as evanescent coupling, which uses optical fiber tapers. In addition, we investigate and analyze the optical birefringence properties of these resonators in the 1.5-micrometer spectral band. Through thermal annealing, silk fibroin undergoes a unique structural transformation from Silk I (amorphous) to Silk II (semi-crystalline). The increase of nano-crystalline sheet structures in Silk II is accompanied by several modifications to this biomaterial's physical (wettability) and optical (birefringence) properties. The photoelasticity of amorphous (Silk I) and semicrystalline Silk (Silk II) is attributed to the emergence of the β-sheet conformations that dominate the Silk II structure. Photo-elastic experiments are performed, tracing the TE and TM shifts of the whispering gallery mode resonances upon applying an axial strain. The strain optical coefficient K’ for Silk I fibroin was found to be 0.059±0.004, with the corresponding value for Silk II being 0.129±0.004.Οι τρόποι εγκλωβισμού ψιθυρισμού του φωτός είναι χρήσιμοι σε διάφορες εφαρμογές λόγω των μοναδικών χαρακτηριστικών τους, όπως ο υψηλός συντελεστής ποιότητας (Q-factor) και η ευαισθησία στις αλλαγές του δείκτη διάθλασης. Η παρούσα διατριβή εξετάζει τη δυνατότητα της αξιοποίησης των τρόποι εγκλωβισμού συντονισμού του φωτός σε κοιλότητες κυλινδρικής συμμετρίας για τη μελέτη άμορφων υλικών, όπως το θερμικά πολωμένου γυαλιού Duran και της αναγεννημένης φιμπροίνης του μεταξιού, και τη σύνδεση αυτών των συντονισμών με τις συγκεκριμένες οπτικές και μηχανικές τους ιδιότητες.Στο πρώτο μέρος της διδακτορικής διατριβής παρουσιάζεται η μελέτη που πραγματοποιήθηκε με τη μέθοδο των τρόπων εγκλωβισμού ψιθυρισμού σε ηλεκτρικά πολωμένες υάλινες οπτικές έτερο-ίνες. Οι ΤΕ και ΤΜ ρυθμοί ανώτερης της μονάδας τάξης των ηλεκτρικά πολωμένων έτερο-ινών υφίστανται έναν φασματικό “καθαρισμό” σε σύγκριση με τη φασματική απόκριση των αρχικών έτερο-ινών. Η συγκεκριμένη φασματική συμπεριφορά των ηλεκτρικά πολωμένων έτερο-ινών αποδίδεται σε αλλαγές του δείκτη διάθλασης οι οποίες λαμβάνουν χώρα κοντά στην περιφέρεια της έτερο-ίνας. Αυτές οι αλλαγές συνδέονται με ακτινικά συμμετρική ανακατανομή των ιόντων που προϋπάρχουν μέσα στην ύαλο, όπως αυτό προέκυψε από την διαδικασία της θερμικής πόλωσης. Οι φασματικές αποκρίσεις των ηλεκτρικά πολωμένων οπτικών κοιλοτήτων προσομοιώθηκαν χρησιμοποιώντας τη μέθοδο πεπερασμένων στοιχείων. Για να διερευνηθούν οι χωρικές αλλαγές της κατανομής των ιόντων και της δομής της ύαλου που λαμβάνουν χώρα στις ηλεκτρικά πολωμένες έτερο-ίνες πραγματοποιήθηκαν μια σειρά από επιπλέον μετρήσεις χαρακτηρισμού της μορφής της ύαλου. Αυτές ήταν οι εξής: μικροσκοπία δεύτερης αρμονικής τάξης (SGH), φασματοσκοπία διασποράς ενέργειας ακτίνων Χ (EDX) και φασματοσκοπία μ-Raman. Οι παραπάνω μετρήσεις αποκάλυψαν ότι υπάρχει μεταβολή στην συγκέντρωση των ιόντων μετά την διαδικασία της θερμικής πόλωσης της υάλου η οποία επιφέρει αλλαγές στην δομή της καθώς και στην συμμετρία του πλέγματος της. Σε αυτήν τη μελέτη αναπτύχθηκαν οπτικές κοιλότητες κατασκευασμένες από φιμπροίνη, οι οποίες υποστηρίζουν τρόπους εγκλωβισμού ψιθυρισμού, εναποτεθειμένες σε γυάλινες οπτικές ίνες. Για την διέγερση των οπτικών αντηχείων μεταξιού χρησιμοποιήθηκαν θερμικά εφελκυσμένες οπτικές ίνες γυαλιού μικρής διαμέτρου (2 μm). Ο οπτικός χαρακτηρισμός των συγκεκριμένων οπτικών αντηχείων μεταξιού έγινε στο φασματικό εύρος των 1.5 μm. Μέσω θερμικής ανόπτησης το μετάξι υφίσταται μια δομική μεταμόρφωση από την άμορφη κατάσταση (μετάξι τύπου I) σε μια ημικρυσταλλική κατάσταση (μετάξι τύπου IΙ). Αυτός ο μετασχηματισμός συνοδεύεται από αρκετές ευδιάκριτες αλλαγές στις οπτικές ιδιότητες αυτού του βιοϋλικού, επιπλέον της αύξησης των δομών νάνο-κρυσταλλικών β-φύλλων στο μετάξι τύπου ΙΙ. Τα φωτοελαστικά πειράματα πραγματοποιήθηκαν καταγράφοντας τις φασματικές μετατοπίσεις των TE και ΤΜ τρόπων εγκλωβισμού ψιθυρισμού καθώς εφαρμόζαμε αξονική τάση στο σύστημα. Από τις παραπάνω μετρήσεις και την οπτική και μηχανική ανάλυση τους προέκυψε ότι ο φωτοελαστικός οπτικός συντελεστής K για το μετάξι τύπου Ι είναι 0.059±0.004 με την αντίστοιχη τιμή για το μετάξι τύπου ΙΙ να είναι 0.129±0.004

Βιβλιογραφική επισκόπηση πρόβλεψη τουριστικών αφίξεων

Περίληψη: Καταγραφή σε πίνακες μεθόδων πρόβλεψης τουριστικών αφίξεων σε σημαντικούς παγκόσμιους τουριστικούς προορισμού

Type 1 Diabetes Mellitus in the SARS-CoV-2 Pandemic: Oxidative Stress as a Major Pathophysiological Mechanism Linked to Adverse Clinical Outcomes

Recent reports have demonstrated the association between type 1 diabetes mellitus (T1DM) and increased morbidity and mortality rates during coronavirus disease (COVID-19) infection, setting a priority of these patients for vaccination. Impaired innate and adaptive immunity observed in T1DM seem to play a major role. Severe, life-threatening COVID-19 disease is characterized by the excessive release of pro-inflammatory cytokines, known as a “cytokine storm”. Patients with T1DM present elevated levels of cytokines including interleukin-1a (IL), IL-1β, IL-2, IL-6 and tumor necrosis factor alpha (TNF-α), suggesting the pre-existence of chronic inflammation, which, in turn, has been considered the major risk factor of adverse COVID-19 outcomes in many cohorts. Even more importantly, oxidative stress is a key player in COVID-19 pathogenesis and determines disease severity. It is well-known that extreme glucose excursions, the prominent feature of T1DM, are a potent mediator of oxidative stress through several pathways including the activation of protein kinase C (PKC) and the increased production of advanced glycation end products (AGEs). Additionally, chronic endothelial dysfunction and the hypercoagulant state observed in T1DM, in combination with the direct damage of endothelial cells by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), may result in endothelial and microcirculation impairment, which contribute to the pathogenesis of acute respiratory syndrome and multi-organ failure. The binding of SARS-CoV-2 to angiotensin converting enzyme 2 (ACE2) receptors in pancreatic b-cells permits the direct destruction of b-cells, which contributes to the development of new-onset diabetes and the induction of diabetic ketoacidosis (DKA) in patients with T1DM. Large clinical studies are required to clarify the exact pathways through which T1DM results in worse COVID-19 outcomes

Plasma nesfatin-1 and DDP-4 levels in patients with coronary artery disease: Kozani study

Background Nesfatin-1, a novel adipokine and dipeptidyl peptidase-4 (DPP4), a mam malian serine protease, are potent factors of atherosclerosis. In the present cross-sectional study, we investigated whether the plasma nesfatin-1 and DPP4 is associated with the prevalence and severity of coronary artery disease (CAD) with and without diabetes mellitus (DM). Methods We consecutively enrolled a total of 240 patients with significant CAD (previous revascularization or angiographically-proven coronary artery stenosis > 50%) presented with either unstable angina (UA, N = 76) or stable chronic CAD (SCAD, N = 165). 85 patients with at least 2 classical cardiovascular risk factors but without significant CAD served as controls. The severity of CAD was assessed using coronary angiography by the Gensini score. Clinical parameters, glycemic and lipid profile, high-sensitivity CRP (hsCRP), nesfatin-1 and DPP4 levels were assayed. Results No differences were found for age, sex, hypertension and diabetes distribution between groups. Low nesfatin-1 levels were found in both CAD groups (UA & SCAD) with respect to controls. The difference between UA and SCAD groups was marginally non-significant. There was a significant increase of DPP4 along UA to SCAD and control groups. Differences between groups remained unchanged in non-diabetic participants. Nesfatin-1 significantly correlated to hsCRP (r = - 0.287, p = 0.036), HOMA-IR (r = - 0.587, p = 0.007) and hyperlipidemia (r = - 0.331, p = 0.034). DPP4 was significantly associated with hs-CRP (r = 0.353 p < 0.001) and FPG (r = 0.202, p = 0.020) in univariate analysis, but those correlations were lost in multiple regression analysis. There was a negative correlation between nesfatin-1 and the severity of CAD, quantified by the Gensini score (r = - 0.511, p < 0.001), but no association was found for DPP4. Conclusions Serum DPP4 levels are increased in patients with CAD, while serum nesfatin-1 levels have a negative association with both the incidence and the severity of CAD. These results are independent of the presence of diabetes mellitus. In addition, both peptides have a strong association with hsCRP. Trial registration ClinicalTrials.gov Identifier: NCT0030617

Whispering gallery mode resonances in thermally poled borosilicate glass optical microcavities

Three-dimensional control in the tuning of the linear and nonlinear properties of optical materials can catalyse the design of new photonic devices. Glasses being the backbone materials for drawing optical fibres, are inherently centrosymmetric, so their nonlinear dielectric susceptibility χ(2) is zero; thermal poling has been used for breaking the symmetry of such amorphous matrixes

The prognostic role of RBP-4 and adiponectin in patients with peripheral arterial disease undergoing lower limb endovascular revascularization

Background RBP4 is an adipokine with an established role in atherosclerosis, while adiponectin has unique anti-inflammatory properties. We investigated the association of RBP4 and adiponectin with the presence of symptomatic peripheral artery disease (PAD) and their possible prognostic role in major adverse cardiovascular events (MACE). Methods We enrolled 168 consecutive patients with symptomatic, established PAD, requiring revascularization by endovascular means of any or both of their lower limbs. 88 age- and sex-matched subjects with less than 2 classical cardiovascular risk factors served as controls. Clinical parameters, glycemic and lipid profile, RBP4 and adiponectin levels were assayed. The occurrence of MACE was recorded during the 6-month follow-up and patients were assigned to MACE and non-MACE subgroups. Results The presence of symptomatic PAD was significantly correlated with age, diabetes, hsCRP, RBP4 and low adiponectin levels (p < 0.05). After adjustment for age, RBP4 (beta = 0.498, p < 0.001), and adiponectin (beta = -0.288, p < 0.001) levels remained as independent predictors of PAD presence in the whole study cohort. At baseline, MACE subgroup appeared with higher RBP-4 and hsCRP serum levels than non-MACE subgroup (p < 0.001), but no differences were detected for adiponectin (p = 0.758). Serum RBP4 levels remained independent predictor of MACE (beta = 0.455, p < 0.001) after adjustment for traditional cardiovascular risk factors. Conclusions High RBP4 and low adiponectin serum levels are independently associated with PAD presence. In addition, RBP4 is an independent predictor of MACE incidence in symptomatic PAD patients

Whispering gallery mode resonances in thermally poled borosilicate glass hetero-fibers

Whispering gallery mode (WGM) resonances in radially, thermally poled glass hetero-fibers, are investigated for the first time. Upon radially oriented thermal poling, both TE and TM polarized responses undergoing a spectral 'cleaning' process, namely higher-order radial modes are being suppressed, or even fully annihilated, compared to the spectral behavior of the pristine fibers. Second-harmonic generation (SHG) microscopy, Energy Dispersive X-Ray Spectroscopy (EDX) and micro-Raman (μ-Raman) measurements were conducted in order to reveal the spatial profile of the structural and optical changes introduced to the thermally poled hetero-fibers, and correlate them with the WGM spectral measurements. The specific selective, mode cleaning behavior is attributed to refractive index changes generated in proximity to the fiber's circumference, which are associated with radially-symmetric ionic re-distribution. The thermally poled hetero-fiber WGM cavities have been rigorously simulated using the finite element method, the calculated modal eigenstates and transmission spectra, further confirm the specific mode selection mechanism, introduced by the azimuthally symmetric thermal, poling process

Prevalence and Prognostic Factors of Stress Hyperglycemia in a Pediatric Population with Acute Illness in Greece—A Prospective Observational Study

Background: stress hyperglycemia (SH) is a relatively frequent finding in pediatric patients. The purpose of this prospective observational study was to identify the prevalence of pediatric SH and its associated risk factors in Greece. Methods: A total of 1005 patients without diabetes who were admitted consecutively for acute illness in a Pediatric Emergency Department were included in the study. Medical history, anthropometric measurements, blood glucose levels, and the medication administered were recorded. A questionnaire was distributed to parents regarding medical and perinatal history and sociodemographic characteristics. Results: There were 72 cases of SH on admission (7.2%) and 39 (3.9%) during hospitalization. Mean age was 6.4 years; 50.3% were male. SH on admission was associated with oral corticosteroid therapy (21.1% vs. 4.7%, p < 0.001), inhaled corticosteroids (12.7% vs. 3%, p < 0.001), and inhaled β2-agonists (30.6% vs. 10.7%, p < 0.001). In-hospital hyperglycemia was associated with oral corticosteroids (adjusted OR = 3.32), inhaled corticosteroids (OR = 10.03) and inhaled β2-agonists (OR = 5.01). Children with asthma were 5.58 and 7.86 times more likely to present admission and in-hospital hyperglycemia, respectively. Conclusions: This is the first report of SH prevalence in pediatric patients in Greece. Asthma, corticosteroids, and β2-agonists significantly increase the risk of SH. No parental factors seem to predispose to SH

The Effects of Different Hormones on Supraventricular and Ventricular Premature Contractions in Healthy Premenopausal Women

Background and Objectives: The effects of gender differences on cardiac parameters have been well-established. In this study, we aimed to evaluate the possible associations of plasma levels of different sex hormones with premature atrial or ventricular contractions in premenopausal women. Materials and Methods: We conducted a prospective study which included women in late reproductive age who presented with palpitations during an eight-month period. A 12-lead electrocardiography, a transthoracic echocardiogram, blood samples, and 24-hour rhythm Holter were conducted on the third day of the menstrual cycle. Results Overall, 93 healthy premenopausal women with a median age of 42 years were enrolled. QTc interval was within normal limits in all patients. The 24 h range of premature atrial contractions (PACs) and premature ventricular contractions (PVCs) was 0–6450 and was 0–21,230, respectively. The median number of PVCs was 540 and the median number of PACs was 212, respectively. In total, 51 patients (54.8%) had a frequency of PVCs > 500/24 h and 37 patients (39.8%) had a frequency of PACs > 500/24 h, respectively. No statistically significant association was shown between any hormone and the frequency of PACs. Regarding PVCs, patients with a PVCs frequency > 500/24 h had higher estradiol levels compared to patients with PVCs less than 500/24 h (median 60 pg/mL versus 42 pg/mL, p = 0.02, OR: 1.01). No association was found between PVCs and other hormones. Conclusions: In premenopausal healthy women, higher estradiol levels are independently associated with increased PVCs. This suggests that estradiol in late reproductive stages may exert proarrhythmic effects