Effect of Rayleigh-scattering distributed feedback in multi-wavelength and tunable Raman fibre lasers

We have demonstrated that a random distributed feedback based on the Rayleigh scattering provides very flat power-versus-wavelength characteristics both in tunable and multiwavelength ultra-long fibre lasers. © 2011 Optical Society of America.

Insights into the influence of solvent polarity on the crystallization of poly(ethylene oxide) spin-coated thin films via in situ grazing incidence wide-angle X-ray scattering

Controlling polymer thin-film morphology and crystallinity is crucial for a wide range of applications, particularly in thin-film organic electronic devices. In this work, the crystallization behavior of a model polymer, poly(ethylene oxide) (PEO), during spin-coating is studied. PEO films were spun-cast from solvents possessing different polarities (chloroform, THF, and methanol) and probed via in situ grazing incidence wide-angle X-ray scattering. The crystallization behavior was found to follow the solvent polarity order (where chloroform < THF < methanol) rather than the solubility order (where THF > chloroform > methanol). When spun-cast from nonpolar chloroform, crystallization largely followed Avrami kinetics, resulting in the formation of morphologies comprising large spherulites. PEO solutions cast from more polar solvents (THF and methanol) do not form well-defined highly crystalline morphologies and are largely amorphous with the presence of small crystalline regions. The difference in morphological development of PEO spun-cast from polar solvents is attributed to clustering phenomena that inhibit polymer crystallization. This work highlights the importance of considering individual components of polymer solubility, rather than simple total solubility, when designing processing routes for the generation of morphologies with optimum crystallinities or morphologies.

Scattering of the laser writing beam in photonic crystal fibre

Point-by-point fibre grating fabrication by femtosecond laser pulses requires tight focusing of the pulses into the core of the fibre. This condition is not easily satisfied in photonic crystal fibres (PCFs) due to the pulse scattering by the holes. In this letter, we present a numerical model of propagation of tightly focused laser beam through PCF in a typical experimental setup. We investigate impact of the numerical aperture of the beam and hole refractive index on the beam scattering and identify optimal conditions for relating the findings to the requirements of grating fabrication. The results explain and quantify recent experimental grating inscription techniques and are indicative of birefringence observed in long-period gratings written by femtosecond laser pulses. © 2010 Elsevier Ltd. All rights reserved.

Raman fiber lasers with a random distributed feedback based on Rayleigh scattering

We demonstrate lasing based on a random distributed feedback due to the Raman amplified Rayleigh backscattering in different types of cavities with and without conventional point-action reflectors. Quasistationary generation of a narrowband spectrum is achieved despite the random nature of the feedback. The generated spectrum is localized at the reflection or gain spectral maxima in schemes with and without point reflectors, respectively. The length limit for a conventional cavity and the minimal pump power required for the lasing based purely on a random distributed feedback are determined. © 2010 The American Physical Society.

A nanoliter volume nuclear magnetic resonance (NMR) system using tunneling magneto-resistive (TMR) sensors to recognize biomolecules

The need to incorporate advanced engineering tools in biology, biochemistry and medicine is in great demand. Many of the existing instruments and tools are usually expensive and require special facilities.^ With the advent of nanotechnology in the past decade, new approaches to develop devices and tools have been generated by academia and industry. ^ One such technology, NMR spectroscopy, has been used by biochemists for more than 2 decades to study the molecular structure of chemical compounds. However, NMR spectrometers are very expensive and require special laboratory rooms for their proper operation. High magnetic fields with strengths in the order of several Tesla make these instruments unaffordable to most research groups.^ This doctoral research proposes a new technology to develop NMR spectrometers that can operate at field strengths of less than 0.5 Tesla using an inexpensive permanent magnet and spin dependent nanoscale magnetic devices. This portable NMR system is intended to analyze samples as small as a few nanoliters.^ The main problem to resolve when downscaling the variables is to obtain an NMR signal with high Signal-To-Noise-Ratio (SNR). A special Tunneling Magneto-Resistive (TMR) sensor design was developed to achieve this goal. The minimum specifications for each component of the proposed NMR system were established. A complete NMR system was designed based on these minimum requirements. The goat was always to find cost effective realistic components. The novel design of the NMR system uses technologies such as Direct Digital Synthesis (DDS), Digital Signal Processing (DSP) and a special Backpropagation Neural Network that finds the best match of the NMR spectrum. The system was designed, calculated and simulated with excellent results.^ In addition, a general method to design TMR Sensors was developed. The technique was automated and a computer program was written to help the designer perform this task interactively.^

Electro and Magneto-Electropolished Surface Micro-Patterning on Binary and Ternary Nitinol

In this study, an Atomic Force Microscopy (AFM) roughness analysis was performed on non-commercial Nitinol alloys with Electropolished (EP) and Magneto-Electropolished (MEP) surface treatments and commercially available stents by measuring Root-Mean-Square (RMS) , Average Roughness (Ra), and Surface Area (SA) values at various dimensional areas on the alloy surfaces, ranging from (800 x 800 nm) to (115 x 115µm), and (800 x 800 nm) to (40 x 40 µm) on the commercial stents. Results showed that NiTi-Ta 10 wt% with an EP surface treatment yielded the highest overall roughness, while the NiTi-Cu 10 wt% alloy had the lowest roughness when analyzed over (115 x 115 µm). Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) analysis revealed unique surface morphologies for surface treated alloys, as well as an aggregation of ternary elements Cr and Cu at grain boundaries in MEP and EP surface treated alloys, and non-surface treated alloys. Such surface micro-patterning on ternary Nitinol alloys could increase cellular adhesion and accelerate surface endothelialization of endovascular stents, thus reducing the likelihood of in-stent restenosis and provide insight into hemodynamic flow regimes and the corrosion behavior of an implantable device influenced from such surface micro-patterns.

Magneto-Electric Nano-Particles for Non-Invasive Brain Stimulation

This paper for the first time discusses a computational study of using magneto-electric (ME) nanoparticles to artificially stimulate the neural activity deep in the brain. The new technology provides a unique way to couple electric signals in the neural network to the magnetic dipoles in the nanoparticles with the purpose to enable a non-invasive approach. Simulations of the effect of ME nanoparticles for non-invasively stimulating the brain of a patient with Parkinson’s Disease to bring the pulsed sequences of the electric field to the levels comparable to those of healthy people show that the optimized values for the concentration of the 20-nm nanoparticles (with the magneto-electric (ME) coefficient of 100 V cm21 Oe21 in the aqueous solution) is 36106 particles/cc, and the frequency of the externally applied 300-Oe magnetic field is 80 Hz.

Weak electron scattering for the 3He-3H transition and the weak nuclear form factors

We calculate the differential cross section for weak electron scattering reaction, e + 3He-' 3H + ve, for energies from 100 MeV to 6 GeV as a function of outgoing nucleus angle from 0 to n/2 radians. We find that the differential cross section at low [q2] increases with electron energy from 0.1 GeV to 6.0 GeV, such that the peak value at 6.0 GeV is approximately 3.2 x 10-40 cm 2 / ster, a factor of 10 larger than the peak value at 0.1 GeV. We also find that the width of the peak falls very rapidly with increasing electron energy. At high [q2] we find that the differential cross section falls by approximately three orders of magnitude making experimental observation at this time unlikely. The contributions of the individual form factors are obtained for electron energies of 0.5GeV and 2.0 GeV. It is found that at low [q2] the form factors, FA(q2) and Fv(q2), make contributions of similar size to the differential cross section and might be simultaneously determined , but for the case of FM(q2) we find that the contribution is too small to determine. It is also found that at large [q2] values, the contribution of FM(q2) is substantially enhanced , but that the cross section is probably too small to enable a direct determination of FM(q2).

Síntese e caracterização de nanopartículas magnéticas de Co e Ni com aplicação em magneto hipertermia

Nanoparticles are importante for the study of new phenomena and for the development of new applications. Metallic magnetic nanoparticles like Cobalt and Nickel are important for their applications in nanoscience and nanotechnology. In this work, we report on the synthesis and characterization of Ni and Co nanoparticles. The nanoparticles were prepared by the modi- ed sol-gel method and were formed in the pore-network of the biopolymer quitosan. The reduction occurred in absence of H2 ux. The metallic particles and their monoxides have a face-centered- cubic structure. The metallic particles sizes ranged from 59 to 77 nm and from 19 to 50 nm for Ni and Co, respectively. Their monoxides chemically passivated the metallic cores, and after several weeks we have not observed further increase in oxidation. The synthesis method was tuned to obtain mainly the ferromagnetic phase. The system behaves like a core/shell structure with a ferromagnetic core and an antiferromagnetic shell. Exchange bias e ect was observed at temperatures below the Néel temperature. Both systems were submitted to an alternated magnetic eld and the heat released by the particles increased the temperature to 140°C in an interval of 5 min. Similar studies in samples dispersed in water increased the temperatures to 40-59°C, these results suggest that these materials are candidates for magnetic hyperthermia.

Studio di stati fotoeccitati in nanoparticelle di V-TiO2 mediante scattering inelastico risonante di raggi X

La TiO2 è uno dei materiali più studiati degli ultimi decenni. I motivi sono da ricercarsi nelle sue numerose applicazioni, possibili in molti campi come dispositivi fotovoltaici, depurazione da agenti inquinanti o filtraggio di raggi UV. Per le celle elettrochimiche in particolare, il biossido di titanio offre molti vantaggi, ma non è privo di ostacoli. Il limite principale è lo scarso assorbimento dello spettro visibile, dovuto all’energy gap elevato (circa 3.2 eV). La ricerca da diversi anni si concentra sul tentativo di aumentare l’assorbimento di luce solare: promettenti sono i risultati raggiunti grazie alla forma nanoparticellare della TiO2, che presenta proprietà diverse dal materiale bulk. Una delle strategie più studiate riguarda il drogaggio tramite impurità, che dovrebbero aumentare le prestazioni di assorbimento del materiale. Gli elementi ritenuti migliori a questo scopo sono il vanadio e l’azoto, che possono essere usati sia singolarmente che in co-doping. In questo lavoro abbiamo realizzato la crescita di nanoparticelle di V-TiO2, tramite Inert Gas Condensation. La morfologia e la struttura atomica sono state analizzate attraverso microscopia a trasmissione, analizzandone la mappe tramite image processing. Successivamente abbiamo studiato le proprietà di assorbimento ottico dei campioni, nello spettro visibile e nel vicino ultravioletto, attraverso il metodo della riflettanza diffusa, determinando poi il bandgap tramite Tauc Plot. L’esperimento centrale di questo lavoro di tesi è stato condotto sulla beamline ID26 dell’European Synchrotron Radiation Facility, a Grenoble. Lì, abbiamo effettuato misure XANES, allo scopo di studiare gli stati fotoeccitati del materiale. L’eccitazione avveniva mediante laser con lunghezza d’onda di 532 nm. Tramite gli spettri, abbiamo analizzato la struttura locale e lo stato di ossidazione del vanadio. Le variazioni indotta dal laser hanno permesso di capire il trasferimento di carica e determinare la vita media.

Controllo ultra-low power di un modulatore back-scattering per applicazioni di localizzazione in sistemi RFID

In questa tesi viene elaborata un'applicazione ultra-low power (ULP) basata su microcontrollore, per implementare la procedura di controllo di diversi circuiti di un tag RFID. Il tag preso in considerazione è pensato per lavorare in assenza di batteria, da cui la necessita' di ridurre i consumi di potenza. La sua attivazione deve essere inoltre comandata attraverso un'architettura Wake up Radio (WuR), in cui un segnale di controllo radio indirizza e attiva il circuito. Nello specifico, la rete di decodifica dell'indirizzo è stata realizzata mediante il modulo di comunicazione seriale del microcontrollore. Nel Capitolo 1 verrà introdotto il tema dell'Energy Harvesting. Nel Capitolo 2 verrà illustrata l'architettura del sistema nel suo complesso. Nel Capitolo 3 verrà spiegato dettagliatamente il funzionamento del microcontrollore scelto. Il Capitolo 4 sarà dedicato al firmware implementato per svolgere le operazioni fondamentali imputate al micro per i compiti di controllo. Verrà inoltre introdotto il codice VHDL sviluppato per emulare l'output del modulo WuR mediante un FPGA della famiglia Cyclone II. Nel Capitolo 5 verrà presentata una stima dei consumi del microcontrollore in funzione dei parametri di configurazione del sistema. Verrà inoltre effettuato un confronto con un altro microcontrollore che in alcune condizioni potrebbe rappresentare iun'alternativa valida di progetto. Nei Capitoli 6 e 7 saranno descritti possibili sviluppi futuri e conclusioni del progetto. Le specifiche di progetto rilevanti della tesi sono: 1. minimo consumo energetico possibile del microcontrollore ULP 2. elevata rapidità di risposta per la ricezione dei tag, per garantire la ricezione di un numero maggiore possibile di indirizzi (almeno 20 letture al secondo), in un range di tempo limitato 3. generazione di un segnale PWM a 100KHz di frequenza di commutazione con duty cycle 50% su cui basare una modulazione in back-scattering.

Application of Inelastic Neutron Scattering to the Methanol-to-Gasoline Reaction Over a ZSM-5 Catalyst

Peer reviewed

Seismic scattering and absorption mapping of debris flows, feeding paths, and tectonic units at Mount St. Helens volcano

Acknowledgments We thank Edoardo Del Pezzo, Ludovic Margerin, Haruo Sato, Mare Yamamoto, Tatsuhiko Saito, Malcolm Hole, and Seth Moran for the valuable suggestions regarding the methodology and interpretation. Greg Waite provided the P wave velocity model of MSH. An important revision of the methods was done after two blind reviews performed before submission. The suggestions of two anonymous reviewers greatly enhanced our ability of imaging structures, interpreting our results, and testing their reliability. The facilities of the IRIS Data Management System, and specifically the IRIS Data Management Center, were used for access to waveform and metadata required in this study, and provided by the Cascades Volcano Observatory – USGS. Interaction with geologists and geographers part of the Landscape Dynamics Theme of the Scottish Alliance for Geoscience, Environment and Society (SAGES) has been important for the interpretation of the results.

Revival resonant scattering, perfect caustics and isotropic transport of pseudospin-1 particles

This work was supported by ONR under Grant No. N00014-16-1-2828.

CW lasing in a telecom fibre due to the random distributed feedback via Rayleigh scattering

We demonstrate a fibre laser with a mirrorless cavity that operates via Rayleigh scattering amplified through the Raman effect. The properties of such random distributed feedback laser appear different from those of both traditional random lasers and conventional fibre lasers. ©2010 IEEE.