Stimulation experiments on the design of highway variable message signs (VMS)

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1996.Includes bibliographical references (leaves 68-69).by Michalis Stavrou Kilaras.M.S

Non-linear optical properties of two-dimensional nanomaterials and other photonic materials

Nonlinear optical (NLO) materials have spanned a wide range of scientific and technological fields, constituting the elementary cornerstones of prominent photonic and optoelectronic devices. Among them, two-dimensional (2D) materials have currently stimulated a dramatically increasing interest owing to their striking optoelectronic characteristics, which endow them with great possibilities in a plethora of pivotal scientific areas, including ultrafast lasing, optical limiting, catalysis, telecommunications, optical information processing and storage, optical computing, to name a few. The pioneer of 2D materials, graphene, being characterized by chemical inertness, zero bandgap and exhibiting dispersibility problems, is of limited use in photonics and optoelectronics. However, there are some graphene derivatives, such as graphene oxide (GO) and graphene acid (GA), being readily dispersible in aqueous and/or other common organic solvents and exhibiting non-zero energy bandgap. They can behave from semiconductors to conductors depending on the ratio of sp2 and sp3 hybridization regions. Thus, the controlled modification of the degree of oxidization and doping with heteroatoms, such as boron and nitrogen, which result in the variation of sp2/sp3 ratio, allow for the tuning of the electronic and optical properties of oxidized graphene, and therefore their nonlinear optical properties. The popularity of graphene has triggered the interest for other graphene-like 2D materials based on other IVA group elements (Si, Ge, Sn, Pb). Among them, the silicon-based counterpart of graphene, namely silicene, has gained great interest as it shares some of the outstanding properties envisaged for graphene. Worth noting, functionalized silicene nanosheets have revealed comparable and even larger NLO response than graphene, emphasizing their potential for 2D-material-based photonics and optoelectronic applications and devices.During last years, 2D materials of the type MX2, with M a transition-metal atom (Mo, W, etc.) and X a chalcogen atom (S, Se, or Te), also known as transition metal dichalcogenides (TMDs), have also triggered the research interest, for their potential for micro-electronics and nano-photonics applications. Layered TMDs, depending on their structural phases (trigonal prismatic-2H or octahedral-1T) exhibit semiconducting or metallic properties. The diversity of crystalline structure and structural phase of the d electrons, as well as the number and type of layer stacking sequences of TMDs, result in a broad range of opto-electronic properties of these van der Waals nanostructures. Consequently, it is reasonably expected that the engineering of crystalline structure of TMDs can modify their NLO response as well. Another class of emerging 2D materials, with very interesting optoelectronic properties is some atomically thin non-van der Waals layered nanostructures, i.e., featuring covalent out-of-plane bonding, which have been successfully exfoliated from naturally grown bulk metal minerals. Among them, hematene and magnetene, the two archetype 2D iron-ore magnetic materials presenting thicknesses down to the atomically thin sheets have very recently attracted the research interest. However, investigations pertaining to their NLO response are still at their early stages. Apart from 2D materials, the last decades have witnessed a great research interest in copper oxide nanohybrids in a dielectric medium. In addition to the outstanding electronic, mechanical, magnetic, and optical properties of these nanohybrids, for excitations close to the surface plasmon frequency, a very large enhancement of the third-order susceptibility is achieved. These properties make these materials suitable for applications in optoelectronics, such as in optical switch devices, detectors, etc. In this dissertation, the nonlinear optical properties of these nanostructures are studied. More specifically, some 2D nanostructures, such as N and/or B-doped graphene oxides, silicon nanosheets, metallic and semiconducting phase TMDs, non-van der Waals layered iron oxides, and copper oxide based nanohybrids were synthesized and characterized using different spectroscopic methods. Then, the NLO response of these nanostructures was investigated in time scales from ns to fs, using Z-scan and pump-probe Optical Kerr effect (OKE) techniques. The results showed that the type and amount of heteroatom doping, the type of functional groups, the crystalline phase, the quantum confinement effects, and the number of layers affect the nonlinear optical response of these systems.Τα υλικά που επιδεικνύουν ισχυρή μη γραμμική οπτική απόκριση (NLO) βρίσκουν εφαρμογή σε ένα ευρύ φάσμα επιστημονικών και τεχνολογικών πεδίων, αποτελώντας τους ακρογωνιαίους λίθους σημαντικών φωτονικών και οπτοηλεκτρονικών διατάξεων. Μεταξύ αυτών, τα δισδιάστατα (2D) υλικά έχουν προσελκύσει ένα εξαιρετικά αυξανόμενο ενδιαφέρον εξαιτίας των εντυπωσιακών οπτοηλεκτρονικών χαρακτηριστικών τους, που τους προσδίδουν εξαιρετικές δυνατότητες σε μία πληθώρα εφαρμογών, όπως π.χ. την παραγωγή υπερβραχέων παλμών λέιζερ, τον οπτικό περιορισμό, την κατάλυση, τις τηλεπικοινωνίες, την οπτική επεξεργασία και αποθήκευση πληροφοριών, την οπτική πληροφορική, κ.α. Tο γραφένιο, το πρώτο 2D υλικό που ανακαλύφθηκε, παρουσιάζει χημική αδράνεια, μηδενικό ενεργειακό χάσμα και έχει περιορισμένη διαλυτότητα σε οργανικούς διαλύτες και στο νερό, χαρακτηριστικά που παρεμποδίζουν την πρακτική εφαρμογή του σε διατάξεις οπτοηλεκτρονικής και φωτονικής. Ωστόσο, υπάρχουν ορισμένα παράγωγα του γραφενίου, όπως το οξείδιο του γραφενίου (GO) και το οξύ του γραφενίου (GA), τα οποία διαλύονται ευκολότερα και παρουσιάζουν διαπερατό ενεργειακό χάσμα. Αυτά μπορούν να συμπεριφέρονται από ημιαγωγοί έως αγωγοί ανάλογα με το ποσοστό των sp2 και sp3 υβριδισμένων ατόμων άνθρακα. Έτσι, η ελεγχόμενη μεταβολή του βαθμού οξείδωσης και η πρόσμιξη με ετεροάτομα βορίου ή/και αζώτου, που οδηγούν σε μεταβολή του λόγου sp2/sp3, μπορεί να επιφέρει σημαντικές αλλαγές στις ηλεκτρικές και οπτικές ιδιότητές τους, και συνεπώς στη μη γραμμική οπτική απόκρισή τους. Η ανακάλυψη του γραφενίου έχει προκαλέσει το ενδιαφέρον για άλλα 2D υλικά που εμφανίζουν παρόμοια δομή με το γραφένιο και αποτελούνται από άλλα στοιχεία της IVΑ ομάδας (Si, Ge, Sn, Pb) του περιοδικού πίνακα. Μεταξύ αυτών, το ανάλογο του γραφενίου με βάση το Si, που ονομάζεται πυριτένιο, έχει κεντρίσει το μεγαλύτερο ενδιαφέρον, καθώς παρουσιάζει ορισμένες από τις μοναδικές ιδιότητες που συναντώνται στο γραφένιο. Μάλιστα, πρόσφατα έχει δειχθεί ότι το πυριτένιο παρουσιάζει συγκρίσιμη ή/και ακόμη ισχυρότερη μη γραμμική οπτική απόκριση από το γραφένιο μέσω της χημικής του τροποποίησης, με αποτέλεσμα να επιδεικνύει καλύτερες προοπτικές για διάφορες εφαρμογές οπτοηλεκτρονικής και φωτονικής. Τα τελευταία χρόνια, τα δισδιάστατα υλικά με χημικό τύπο MX2, όπου με Μ συμβολίζεται ένα άτομο μετάλλου μετάπτωσης (Mo, W, κ.λπ.) και με Χ ένα άτομο χαλκογόνου (S, Se ή Te), γνωστά και ως διχαλκογενίδια των μετάλλων μετάπτωσης (TMDs), έχουν επίσης προσελκύσει το ερευνητικό ενδιαφέρον, εξαιτίας των δυνατοτήτων τους στον τομέα της νανοτεχνολογίας. Αξίζει να σημειωθεί ότι τα TMDs παρουσιάζουν, σε μεγάλο βαθμό, μεταβλητές οπτικές και ηλεκτρονικές ιδιότητες, που καθορίζονται από τον πολυμορφισμό της κρυσταλλικής δομής τους και τον αριθμό των d-ηλεκτρονίων των μετάλλων μετάπτωσης. Επομένως, αναμένεται εύλογα ότι η τροποποίηση της κρυσταλλικής δομής των TMDs μπορεί επίσης να επιφέρει τη δραστική μεταβολή της μη γραμμικής τους απόκρισης. Μια ξεχωριστή κατηγορία αναδυόμενων υλικών είναι τα non-van der Waals 2D υλικά. Αυτές οι 2D νανοδομές έχουν αποφλοιωθεί επιτυχώς από μεταλλεύματα μετάλλων των οποίων τα γειτονικά ατομικά επίπεδα συνδέονται μεταξύ τους με ομοιοπολικούς δεσμούς. Tο αιματένιο και το μαγνητένιο, τα δύο αρχέτυπα 2D μαγνητικά υλικά που παρουσιάζουν ατομικό πάχος, έχουν προσελκύσει πολύ πρόσφατα το ερευνητικό ενδιαφέρον. Ωστόσο, η μελέτη των μη γραμμικών οπτικών ιδιοτήτων τους βρίσκεται ακόμη σε πολύ πρώιμο στάδιο.Εκτός από τα δισδιάστατα υλικά, τις τελευταίες δεκαετίες παρατηρείται μεγάλο ερευνητικό ενδιαφέρον για τα νανοσωματίδια οξειδίου του χαλκού σε διηλεκτρικό μέσο. Εκτός από τις εξαιρετικές ηλεκτρικές, μηχανικές, μαγνητικές και οπτικές ιδιότητες αυτών των υλικών, για διεγέρσεις κοντά στη συχνότητα των επιφανειακών πλασμονίων, επιτυγχάνεται πολύ μεγάλη ενίσχυση της επιδεκτικότητας τρίτης τάξης. Οι ιδιότητες αυτές καθιστούν τα υλικά αυτά κατάλληλα για εφαρμογές σε διατάξεις οπτικού διακόπτη, ανιχνευτές κ.λπ. Στην παρούσα διδακτορική διατριβή διερευνώνται οι μη γραμμικές οπτικές ιδιότητες αυτών των νανοδομών. Πιο συγκεκριμένα, σε αυτή τη μελέτη συντέθηκαν και χαρακτηρίστηκαν με διάφορες φασματοσκοπικές μεθόδους, οξείδια του γραφενίου με διαφορετικά ποσοστά προσμίξεων Β ή/και Ν, χημικά τροποποιημένα πυριτένια, ορισμένα TMDs μεταλλικής και ημιαγώγιμης φάσης, ορισμένα non-van der Waals 2D υλικά και ορισμένα νανοσωματίδια οξειδίου του χαλκού. Έπειτα, χρησιμοποιήθηκαν παλμικές οπτικές διεγέρσεις σε διαφορετικές χρονικές κλίμακες εκτεινόμενες από ns (10-9s) έως fs (10-15s) για την μελέτη των μη γραμμικών οπτικών ιδιοτήτων τους μέσω των τεχνικών Z-scan και οπτικού φαινομένου Kerr (OKE). Τα αποτελέσματα έδειξαν ότι διάφοροι παράγοντες όπως το είδος και το ποσοστό των προσμίξεων ετεροατόμων, το είδος της χημικής τροποποίησης, η κρυσταλλική φάση, τα φαινόμενα κβαντικού περιορισμού και ο αριθμός των φύλλων, επηρεάζουν τη μη γραμμική οπτική απόκριση αυτών των συστημάτων

N-doped graphene and N-doped graphene acid: Heteroatom doping for very efficient broad-band optical limiting performance from UV to NIR

The present work reports on the exceptional optical limiting performance of some recently synthesized nitrogen-doped graphene derivatives (NGs) by substitutional heteroatom doping. In particular, the optical limiting performance of NGs having different nitrogen contents and some NG-based quantum dots is investigated in a broad-band spectral range, from 355 to 1850 nm, using 4 ns laser pulses. The obtained results show that the present N-doped graphene derivatives exhibit very efficient broad-band optical limiting performance, attaining record low values of optical limiting onset (OLon), in particular for NIR wavelengths, significantly lower than those of other previously studied graphene derivatives and other families of benchmark materials for optical limiting. The present results demonstrate that tuning the N-doping of graphene acid is a very powerful and efficient strategy for the enhancement of the OL action of graphene, rendering it the strongest currently known optical limiting material, improving dramatically its potential for various optoelectronic and photonic applications.Web of Science12633143451433

Crystalline phase effects on the nonlinear optical response of MoS2 and WS2 nanosheets: Implications for photonic and optoelectronic applications

In the present work, some MoS2 and WS2 nanosheets were prepared and characterized. Depending on the preparation procedures, trigonal prismatic (2H) or octahedral (1T) coordination of the metal atoms was obtained, exhibiting metallic (1T) or semiconducting (2H) character. Both MoS2 and WS2 nanosheets were found exhibiting large nonlinear optical (NLO) responses, strongly dependent on their metallic (1T) or semiconducting (2H) character. Therefore, the semiconducting character of MoS2 and WS2 exhibits positive nonlinear absorption and strong self-focusing behavior, while their metallic character counterparts exhibit strong negative nonlinear absorption and important self-defocusing behavior. In addition, the semiconducting MoS2 and WS2 were found exhibiting important and very broadband optical limiting (OL) action extending from 450 to 1750 nm. Therefore, by selecting the crystalline phase of the nanosheets, that is, their semiconduction/metallic character, their NLO response can be greatly modulated. The results of the present work demonstrate unambiguously that the control of the crystalline phase of MoS2 and WS2 provides an efficient strategy for 2D nanostructures with custom-made NLO properties for specific optoelectronic and photonic applications such as OL, saturable absorption, and optical switching.M.S. acknowledges support from the Hellenic Foundation for Research and Innovation (HFRI) under the HFRI PhD Fellowship grant (number: 83656). Financial support to N.T. by the Hellenic Foundation for Research and Innovation HFRI under the “2nd Call for HFRI Research Projects to support Faculty Members and Researchers” (Project number: 2482) is acknowledged. TEM studies were performed in Laboratorio de Microscopias Avanzadas (LMA), Universidad de Zaragoza, Spain. R.A. acknowledges support from Spanish MICINN (PID2019-104739GB–100/AEI/10.13039/501100011033), Government of Aragon (projects DGA E13-20R), and from EU H2020 “ESTEEM3” (Grant number 823717) and Graphene Flagship (Grant number 881603).Peer reviewe

Silicon Nanosheets: An Emerging 2D Photonic Material with a Large Transient Nonlinear Optical Response beyond Graphene

The present work reports on the transient nonlinear optical (NLO) responses of two different types of 2D silicon nanosheets (SiNSs), namely hydride-terminated silicon nanosheets (SiNS–H) and 1-dodecene-functionalized silicon nanosheets (SiNS–dodecene). The main motivation of this study was to extend the knowledge regarding the NLO properties of these Si–based materials, for which very few published studies exist so far. For that purpose, the NLO responses of SiNS–H and SiNS–dodecene were investigated experimentally in the nanosecond regime at 532 and 1064 nm using the Z-scan technique, while the obtained results were compared to those of certain recently studied graphene nanosheets. SiNS–dodecene was found to exhibit the largest third-order susceptibility χ(3) values at both excitation wavelengths, most probably ascribed to the presence of point defects, indicating the importance of chemical functionalization for the efficient enhancement and tailoring of the NLO properties of these emerging 2D Si-based materials. Most importantly, the results demonstrated that the present silicon nanosheets revealed comparable and even larger NLO responses than graphene nanosheets. Undoubtedly, SiNSs could be strong competitors of graphene for applications in 2D-material-based photonics and optoelectronics

COL4A5 and LAMA5 variants co-inherited in familial hematuria: digenic inheritance or genetic modifier effect?

Abstract Background About 40–50% of patients with familial microscopic hematuria (FMH) caused by thin basement membrane nephropathy (TBMN) inherit heterozygous mutations in collagen IV genes (COL4A3, COL4A4). On long follow-up, the full phenotypic spectrum of these patients varies a lot, ranging from isolated MH or MH plus low-grade proteinuria to chronic renal failure of variable degree, including end-stage renal disease (ESRD). Methods Here, we performed Whole Exome Sequencing (WES) in patients of six families, presenting with autosomal dominant FMH, with or without progression to proteinuria and loss of renal function, all previously found negative for severe collagen IV mutations. Hierarchical filtering of the WES data was performed, followed by mutation prediction analysis, Sanger sequencing and genetic segregation analysis. Results In one family with four patients, we found evidence for the contribution of two co-inherited variants in two crucial genes expressed in the glomerular basement membrane (GBM); LAMA5-p.Pro1243Leu and COL4A5-p.Asp654Tyr. Mutations in COL4A5 cause classical X-linked Alport Syndrome, while rare mutations in the LAMA5 have been reported in patients with focal segmental glomerulosclerosis. The phenotypic spectrum of the patients includes hematuria, proteinuria, focal segmental glomerulosclerosis, loss of kidney function and renal cortical cysts. Conclusions A modifier role of LAMA5 on the background of a hypomorphic Alport syndrome causing mutation is a possible explanation of our findings. Digenic inheritance is another scenario, following the concept that mutations at both loci more accurately explain the spectrum of symptoms, but further investigation is needed under this concept. This is the third report linking a LAMA5 variant with human renal disease and expanding the spectrum of genes involved in glomerular pathologies accompanied by familial hematurias. The cystic phenotype overlaps with that of a mouse model, which carried a Lama5 hypomorphic mutation that caused severely reduced Lama5 protein levels and produced kidney cysts

Supervised Versus Unsupervised Pulmonary Rehabilitation in Patients with Pulmonary Embolism: A Valuable Alternative in COVID Era

The aim of our study was to assess the effect of 8 weeks of pulmonary rehabilitation (PR) in patients with pulmonary embolism (PE) during unsupervised PR (unSPRgroup) versus supervised PR (SPRgroup) on cardiopulmonary exercise testing (CPET) parameters, sleep quality, quality of life and cardiac biomarkers (NT-pro-BNP). Fourteen patients with PE (unSPRgroup, n = 7, vs. SPRgroup, n = 7) were included in our study (age, 50.7 ± 15.1 years; BMI, 30.0 ± 3.3 kg/m2). We recorded anthropometric characteristics and questionnaires (Quality of life (SF-36) and Pittsburg sleep quality index (PSQI)), we performed blood sampling for NT-pro-BNP measurement and underwent CPET until exhausting before and after the PR program. All patients were subjected to transthoracic echocardiography prior to PR. The SPRgroup differed in mean arterial pressure at rest before and after the PR program (87.6 ± 3.3 vs. 95.0 ± 5.5, respectively, p = 0.010). Patients showed increased levels of leg fatigue (rated after CPET) before and after PR (p = 0.043 for SPRgroup, p = 0.047 for unSPRgroup) while the two groups differed between each other (p = 0.006 for post PR score). Both groups showed increased levels in SF-36 scores (general health; p = 0.032 for SPRgroup, p = 0.010 for unSPRgroup; physical health; p = 0.009 for SPRgroup, p = 0.022 for unSPRgroup) and reduced levels in PSQI (cannot get to sleep within 30-min; p = 0.046 for SPRgroup, p = 0.007 for unSPRgroup; keep up enough enthusiasm to get things done; p = 0.005 for SPRgroup, p = 0.010 for unSPRgroup) following the PR program. The ΝT-pro-BNP was not significantly different before and after PR or between groups. PR may present a safe intervention in patients with PE. The PR results are similar in SPRgroup and unSPRgroup

Additional file 1: of COL4A5 and LAMA5 variants co-inherited in familial hematuria: digenic inheritance or genetic modifier effect?

WES statistics. Number of genetic variants called after the WES analysis. (DOCX 15 kb