Low-cost, precision, self-alignment technique for coupling laser and photodiode arrays to polymer waveguide arrays on multilayer PCBs

The first, to our knowledge, passive, precision, self-alignment technique for direct coupling of vertical cavity surface emitting laser (VCSEL) and photodiode (PD) arrays to an array of polymer buried channel waveguides on a rigid printed circuit board (PCB) is reported. It gives insertion losses as good as the best achieved previously, to within experimental measurement accuracy, but without the need for costly active alignment nor waveguide facet polishing and so is a major step towards a commercially realizable low cost connector. Such an optical connector with four duplex channels each operating at 10 Gb/s (80 Gb/s aggregate) was designed, constructed, and its alignment precision assessed. The alignment technique is applicable to polymer waveguide interconnections on both rigid and flexible multilayer printed circuit boards (PCBs). The dependence of optical coupling loss on mis-alignments in x, y and z of the VCSEL and PD arrays allows the precision of alignment to be assessed and its reproducibility on multiple mating cycles of the connector is reported. The first recorded measurements of crosstalk between waveguides when the connector is misaligned are reported. Lateral misalignments of the connector to within its tolerance are shown to have no effect on the signal to crosstalk ratio (SCR), to within experimental measurement accuracy. The insertion loss repeatability is similar to that of single mode fiber mechanically transferable (MT) connectors

Στατική και Δυναμική Ευστάθεια του Πύργου της Πίζας

Στην παρούσα διπλωματική εργασία μελετάται με αριθμητική προσομοίωση πεπερασμένων στοιχείων η ευστάθεια του Πύργου της Πίζας στην Ιταλία, η οποία έχει αποτελέσει μία πρόκληση για την επιστήμη του μηχανικού. Ο Πύργος εδράζεται πάνω σε αδύναμο και αρκετά συμπιεστό έδαφος και η κλίση του αυξάνεται διαρκώς με τα χρόνια μέχρι τη σημερινή του κατάσταση. Η ιστορία της κατασκευής του και της εξέλιξης της κλίσης του είναι σημαντικά για την κατανόηση αυτού του φαινομένου. Για να προσομοιωθεί η πραγματική κατάσταση του Πύργου χρησιμοποιούνται οι πραγματικές ιδιότητες του εδάφους και της ανωδομής, όπως έχουν προκύψει από επί τόπου μετρήσεις στην ευρύτερη περιοχή του Πύργου της Πίζας, καθώς και στον Πύργο. Χρησιμοποιείται ο κώδικας πεπερασμένων στοιχείων του Abaqus και εφαρμόζονται στατικές και δυναμικές φορτίσεις. Στην παρούσα διπλωματική ερμηνεύεται η σημερινή κατάσταση του Πύργου, όσον αφορά τους μηχανισμούς αστοχίας του εδάφους, καθώς και την επιρροή της ανωδομής. Πιο συγκεκριμένα, γίνεται κατανοητή η επίδραση της αστάθειας λόγω της κλίσης του Πύργου, η οποία όσο αυξάνεται αυξάνει την ροπή ανατροπής που επιβάλλεται στο θεμέλιο (φαινόμενα P - δ). Επιπλέον, χρησιμοποιούνται ποικίλοι καταστατικοί νόμοι για το έδαφος, ώστε να γίνει δυνατή η σωστή προσομοίωση της πραγματικής κατάστασης του εδάφους. Τα αποτελέσματα παρουσιάζονται με τη μορφή καθιζήσεων, στροφής καθώς και τάσεων κάτω από το θεμέλιο, ώστε να ερμηνευτεί η στατική ευστάθεια του Πύργου της Πίζας. Διερευνάται επιπλέον η σεισμική απόκριση του Πύργου μέσω ρεαλιστικών διεγέρσεων για την ευρύτερη περιοχή, καθώς και με τη χρήση παλμών. Παρατηρείται πως η συμπεριφορά της ανωδομής είναι αποδεκτή, καθώς η επιτάχυνση που φτάνει σε αυτή είναι αρκετά μειωμένη. Αυτό συμβαίνει διότι ο Πύργος είναι υψίκορμος με μεγάλη ιδιοπερίοδο. Ωστόσο, η κλίση του καθώς και η καθιζήσεις αυξάνονται. Τέλος, γίνεται σύγκριση μεταξύ των αναλύσεων 2D και 3D.In this diploma thesis we analyze the stability of the Leaning Tower of Pisa in Italy, which has been a very difficult challenge for geotechnical engineering. The system is modeled with numerical finite elements. The Tower is founded on weak, highly compressible soil and its inclination has been increasing inexorably over the years to the point at which is standing today. The history of its construction and its inclination are significant for the understanding of this phenomenon. The real state of the Tower nowadays is achieved using the characteristics of the soil and the superstructure as they have measured from the in situ tests in the vicinity of the Tower of Pisa and the Tower as well. The finite element code of Abaqus is used and static and dynamic loading are applied. In the present diploma thesis the current condition of the Tower is interpreted, concerning the bearing – capacity failure mechanisms in the soil and the effect of the superstructure in this phenomenon. To be more specific, the detrimental effect of the leaning instability of the superstructure to increase the overturning moment on the footing as the inclination rises (phenomena P – δ) is also accounted for. Furthermore, various constitutive models are used, in order to achieve the accurate simulation of the behavior of the soil underneath the Tower of Pisa. The results are presented mainly in the form of displacements, rotation and stresses under the footing, so that the static stability of the Tower will be able to become understood. The seismic performance of the Tower is also explored through realistic excitations for the surrounding vicinity and trough pulses, as well. It is observed that the behavior of the superstructure is acceptable, since the acceleration transmitted to the superstructure is reduced. That is because the Tower is slender with big natural period. However, its inclination and the displacements increase. Finally, comparison between 2D and 3D analyses are made.Αρετή Δ. Παπακωνσταντίνο

FirstLight: Pluggable Optical Interconnect Technologies for Polymeric Electro-Optical Printed Circuit Boards in Data Centers

The protocol data rate governing data storage devices will increase to over 12 Gb/s by 2013 thereby imposing unmanageable cost and performance burdens on future digital data storage systems. The resulting performance bottleneck can be substantially reduced by conveying high-speed data optically instead of electronically. A novel active pluggable 82.5 Gb/s aggregate bit rate optical connector technology, the design and fabrication of a compact electro-optical printed circuit board to meet exacting specifications, and a method for low cost, high precision, passive optical assembly are presented. A demonstration platform was constructed to assess the viability of embedded electro-optical midplane technology in such systems including the first ever demonstration of a pluggable active optical waveguide printed circuit board connector. High-speed optical data transfer at 10.3125 Gb/s was demonstrated through a complex polymer waveguide interconnect layer embedded into a 262 mm × 240 mm × 4.3 mm electro-optical midplane. Bit error rates of less than 10-12 and optical losses as low as 6 dB were demonstrated through nine multimode polymer wave guides with an aggregate data bandwidth of 92.8125 Gb/s

Isoscalar dipole coherence at low energies and forbidden E1 strength

In 16O and 40Ca an isoscalar, low-energy dipole transition (IS-LED) exhausting approximately 4% of the isoscalar dipole (ISD) energy-weighted sum rule is experimentally known, but conspicuously absent from recent theoretical investigations of ISD strength. The IS-LED mode coincides with the so-called isospin-forbidden E1 transition. We report that for N=Z nuclei up to 100Sn the fully self-consistent Random-Phase-Approximation with finite-range forces, phenomenological and realistic, yields a collective IS-LED mode, typically overestimating its excitation energy, but correctly describing its IS strength and electroexcitation form factor. The presence of E1 strength is solely due to the Coulomb interaction between the protons and the resulting isospin-symmetry breaking. The smallness of its value is related to the form of the transition density, due to translational invariance. The calculated values of E1 and ISD strength carried by the IS-LED depend on the effective interaction used. Attention is drawn to the possibility that in N-not-equal-Z nuclei this distinct mode of IS surface vibration can develop as such or mix strongly with skin modes and thus influence the pygmy dipole strength as well as the ISD strength function. In general, theoretical models currently in use may be unfit to predict its precise position and strength, if at all its existence.Comment: 9 pages, 6 figures, EPJA submitte

The statistical importance of a study for a network meta-analysis estimate.

BACKGROUND In pairwise meta-analysis, the contribution of each study to the pooled estimate is given by its weight, which is based on the inverse variance of the estimate from that study. For network meta-analysis (NMA), the contribution of direct (and indirect) evidence is easily obtained from the diagonal elements of a hat matrix. It is, however, not fully clear how to generalize this to the percentage contribution of each study to a NMA estimate. METHODS We define the importance of each study for a NMA estimate by the reduction of the estimate's variance when adding the given study to the others. An equivalent interpretation is the relative loss in precision when the study is left out. Importances are values between 0 and 1. An importance of 1 means that the study is an essential link of the pathway in the network connecting one of the treatments with another. RESULTS Importances can be defined for two-stage and one-stage NMA. These numbers in general do not add to one and thus cannot be interpreted as 'percentage contributions'. After briefly discussing other available approaches, we question whether it is possible to obtain unique percentage contributions for NMA. CONCLUSIONS Importances generalize the concept of weights in pairwise meta-analysis in a natural way. Moreover, they are uniquely defined, easily calculated, and have an intuitive interpretation. We give some real examples for illustration

Re(I) tricarbonyl complex of 1,10-phenanthroline-5,6-dione: DNA binding, cytotoxicity, antiinflammatory and anti-coagulant effects towards platelet activating factor

The complex fac-[Re(CO)3(phendione)Cl] (1) (where phendione = 1,10-phenanthroline-5,6-dione) has been synthesized and fully characterized by UV–visible, FTIR, and NMR techniques. The DNA binding properties of 1 are investigated by UV-spectrophotometric (melting curves), covalent binding assay, CV (cyclic voltammetry), circular dichroism (CD) and viscosity measurements. Experimental data indicate that 1 fits into the major groove without disrupting the helical structure of the B-DNA in contrast to the free phendione which intercalates within the base pairs of DNA. Upon irradiation, complex 1promotes the cleavage of plasmid pBR322 DNA from supercoiled form I to nicked form II via a proton coupled electron transfer mechanism. This comes as a result of experimental data in anaerobic/aerobic conditions and in the presence of DMSO. The biological activities of 1 and its precursors [Re(CO)5Cl] and phendione are tested towards a series of cancerous cell lines as glioblastoma (T98G), prostate cancer (PC3) and breast cancer (MCF-7) as well as platelet activating factor (PAF)-aggregation. Moreover, all the aforementioned compounds are tested for their ability to modulate PAF-basic metabolic enzyme activities in preparations of rabbit leukolytes. The in vitro experiments indicate that phendione has a better antitumor effect than cisplatin whereas [Re(CO)5Cl] is a better PAF inhibitor than both the phendione ligand and 1. Moreover, for the first time it is indicated that [Re(CO)5Cl], with a IC50 of 17 nM is comparable to the widely used PAF receptor antagonists, BN52021 and WEB2170 with IC50 of 30 and 20 nM, respectively, whereas 1 affects PAF-catabolism

Unique and universal dew-repellency of nanocones

Surface structuring provides a broad range of water-repellent materials known for their ability to reflect millimetre-sized raindrops. Dispelling water at the considerably reduced scale of fog or dew, however, constitutes a significant challenge, owing to the comparable size of droplets and structures. Nonetheless, a surface comprising nanocones was recently reported to exhibit strong anti-fogging behaviour, unlike pillars of the same size. To elucidate the origin of these differences, we systematically compare families of nanotexture that transition from pillars to sharp cones. Through environmental electron microscopy and modelling, we show that microdroplets condensing on sharp cones adopt a highly non-adhesive state, even at radii as low as 1.5 µm, contrasting with the behaviour on pillars where pinning results in impedance of droplet ejection. We establish the antifogging abilities to be universal over the range of our cone geometries, which speaks to the unique character of the nanocone geometry to repel dew. Truncated cones are finally shown to provide both pinning and a high degree of hydrophobicity, opposing characteristics that lead to a different, yet efficient, mechanism of dew ejection that relies on multiple coalescences

Universality of the Ising and the S=1 model on Archimedean lattices: A Monte Carlo determination

The Ising model S=1/2 and the S=1 model are studied by efficient Monte Carlo schemes on the (3,4,6,4) and the (3,3,3,3,6) Archimedean lattices. The algorithms used, a hybrid Metropolis-Wolff algorithm and a parallel tempering protocol, are briefly described and compared with the simple Metropolis algorithm. Accurate Monte Carlo data are produced at the exact critical temperatures of the Ising model for these lattices. Their finite-size analysis provide, with high accuracy, all critical exponents which, as expected, are the same with the well known 2d Ising model exact values. A detailed finite-size scaling analysis of our Monte Carlo data for the S=1 model on the same lattices provides very clear evidence that this model obeys, also very well, the 2d Ising model critical exponents. As a result, we find that recent Monte Carlo simulations and attempts to define effective dimensionality for the S=1 model on these lattices are misleading. Accurate estimates are obtained for the critical amplitudes of the logarithmic expansions of the specific heat for both models on the two Archimedean lattices.Comment: 9 pages, 11 figure

Intelligent Multifunctional VO2/SiO2/TiO2 Coatings for Self-Cleaning, Energy-Saving Window Panels

Monoclinic vanadium(IV) oxide (VO2) has received much attention for applications as intelligent solar control coatings, with the potential to reduce the need for both heating and air conditioning loads within building infrastructure. Chemical vapor deposition, a high-throughput industrially scalable method, is an ideal technology for the deposition of VO2 thin films on window panels. However, these films suffer from poor adhesion and are chemically susceptible to attack. In addition, the VO2 films with optimum solar modulation are unfortunately translucent, restraining their commercial use in energy-efficient fenestration. In this work, multifunctional, robust, layered VO2/SiO2/TiO2 films were quickly deposited on glass substrates using atmospheric-pressure chemical vapor deposition and fully characterized using structural, vibrational spectroscopy, and electron microscopy techniques. The VO2/SiO2/TiO2 thin films were designed to exhibit excellent solar modulation properties as well as high transparency and resistance to abrasion, compared to single VO2 films of the same thickness. The films also showed self-cleaning properties comparable to those of commercial Pilkington Activ glass, as demonstrated here during the photodegradation of a model organic pollutant (stearic acid). The SiO2 acted as a barrier layer, preventing the diffusion of Ti4+ ions into the VO2 layer but it also promoted the optical properties and allowed for superior thermochromic behavior when compared to single VO2 films. The system was modeled to determine the effect of the individual components on the properties of the overall material. It was found that the deposition of the SiO2/TiO2 overlayer resulted in a dramatic improvement of visible-light transmission (∼30% increase when compared to single-layer analogues) while also doubling the solar modulation of the material