Análise in vitro da morfologia e da resistência de união da resina composta à dentina erodida e irradiada com laser de Er:YAG com largura de pulso super curta

Lesões dentais por erosão têm sido cada vez mais presentes na prática clínica. A restauração direta com resina composta é uma das opções de tratamento para lesões severas, em que há comprometimento estético/funcional. Com o aprimoramento da tecnologia, a utilização do laser para pré-tratamento da superfície dentinária, antes do condicionamento ácido, tem sido considerada como método alternativo para melhorar a adesão das resinas compostas às superfícies erodidas. Assim, o objetivo deste estudo in vitro foi avaliar a influência da irradiação com laser de Er:YAG (2,94 ?m), de pulso super-curto, na adesão da resina composta à superfície dentinária erodida. Quarenta e seis discos de dentina foram obtidos a partir de 46 dentes terceiros molares humanos. A dentina oclusal planificada de 40 molares humanos teve metade de sua face protegida com fita UPVC (dentina hígida), enquanto na outra metade foi produzida uma lesão de erosão através da ciclagem em ácido cítrico (0,05 M, pH 2,3, 10 minutos, 6x/dia) e solução supersaturada (pH 7,0, 60 minutos entre os ataques ácidos). Metade das amostras foi irradiada com o laser de Er:YAG (50 ?s, 2 Hz, 80 mJ, 12,6 J/cm2) e a outra não (grupo controle). Em cada grupo de tratamento (laser ou controle) (n=10), um sistema adesivo autocondicionante foi utilizado e, então, confeccionados 2 cilindros de resina composta, tanto do lado erodido como no hígido (total de 4 cilindros), os quais foram submetidos à avaliação da Resistência de União através do ensaio de microcisalhamento (1 mm/min), após armazenamento em saliva artificial por 24 h. A análise do padrão de fratura foi realizada em microscópio óptico (40x). Por meio da Microscopia Eletrônica de Varredura (MEV), a morfologia das superfícies dentinárias hígida e submetida ao desafio erosivo, antes e após o tratamento com laser de Er:YAG (n=3), foi avaliada. Os valores obtidos de resistência de união (MPa) foram submetidos ao teste ANOVA e de comparações múltiplas de Tukey (p<0,05) e as análises das eletromicrografias foram feitas de forma descritiva. A análise morfológica da superfície mostrou alterações significativas na dentina hígida irradiada e na submetida à ciclagem erosiva, irradiada ou não. Quanto à resistência de união, houve diferença entre os 4 substratos analisados, sendo: dentina hígida irradiada (12,77±5,09 A), dentina hígida não irradiada (9,76±3,39 B), dentina erodida irradiada (7,62±3,39 C) e dentina erodida não irradiada (5,12±1,72 D). Houve predominância de padrão de fratura do tipo adesiva. Com base nos resultados e nos parâmetros de irradiação utilizados neste estudo, pode-se concluir que a erosão reduz a adesão em dentina e que o tratamento da superfície dentinária com laser de Er:YAG de largura de pulso super curta aumenta a adesão no substrato erodido ou hígido.

The imprint of the crustal magnetic field on the thermal spectra and pulse profiles of isolated neutron stars

Isolated neutron stars (NSs) show a bewildering variety of astrophysical manifestations, presumably shaped by the magnetic field strength and topology at birth. Here, using state-of-the-art calculations of the coupled magnetic and thermal evolution of NSs, we compute the thermal spectra and pulse profiles expected for a variety of initial magnetic field configurations. In particular, we contrast models with purely poloidal magnetic fields to models dominated by a strong internal toroidal component. We find that, while the former displays double-peaked profiles and very low pulsed fractions, in the latter, the anisotropy in the surface temperature produced by the toroidal field often results in a single pulse profile, with pulsed fractions that can exceed the 50–60 per cent level even for perfectly isotropic local emission. We further use our theoretical results to generate simulated ‘observed’ spectra, and show that blackbody (BB) fits result in inferred radii that can be significantly smaller than the actual NS radius, even as low as ∼1–2 km for old NSs with strong internal toroidal fields and a high absorption column density along their line of sight. We compute the size of the inferred BB radius for a few representative magnetic field configurations, NS ages and magnitudes of the column density. Our theoretical results are of direct relevance to the interpretation of X-ray observations of isolated NSs, as well as to the constraints on the equation of state of dense matter through radius measurements.

Simultaneous ultrafast optical pulse train bursts generation and shaping based on Fourier series developments using superimposed fiber Bragg gratings

We propose an all-fiber method for the generation of ultrafast shaped pulse train bursts from a single pulse based on Fourier Series Developments (FDSs). The implementation of the FSD based filter only requires the use of a very simple non apodized Superimposed Fiber Bragg Grating (S-FBG) for the generation of the Shaped Output Pulse Train Burst (SOPTB). In this approach, the shape, the period and the temporal length of the generated SOPTB have no dependency on the input pulse rate.

Ultra-long mode-locked Er-droped fibre lasers

The development of ultra-long (UL) cavity (hundreds of meters to several kilometres) mode-locked fibre lasers for the generation of high-energy light pulses with relatively low (sub-megahertz) repetition rates has emerged as a new rapidly advancing area of laser physics. The first demonstration of high pulse energy laser of this type was followed by a number of publications from many research groups on long-cavity Ytterbium and Erbium lasers featuring a variety of configurations with rather different mode-locked operations. The substantial interest to this new approach is stimulated both by non-trivial underlying physics and by the potential of high pulse energy laser sources with unique parameters for a range of applications in industry, bio-medicine, metrology and telecommunications. It is well known, that pulse generation regimes in mode-locked fibre lasers are determined by the intra-cavity balance between the effects of dispersion and non-linearity, and the processes of energy attenuation and amplification. The highest per-pulse energy has been achieved in normal-dispersion UL fibre lasers mode-locked through nonlinear polarization evolution (NPE) for self-modelocking operation. In such lasers are generated the so-called dissipative optical solitons. The uncompensated net normal dispersion in long-cavity resonatorsusually leads to very high chirp and, consequently, to a relatively long duration of generated pulses. This thesis presents the results of research Er-doped ultra-long (more than 1 km cavity length) fibre lasers mode-locked based on NPE. The self-mode-locked erbium-based 3.5-km-long all-fiber laser with the 1.7 µJ pulse energy at a wavelength of 1.55 µm was developed as a part of this research. It has resulted in direct generation of short laser pulses with an ultralow repetition rate of 35.1 kHz. The laser cavity has net normal-dispersion and has been fabricated from commercially-available telecom fibers and optical-fiber elements. Its unconventional linear-ring design with compensation for polarization instability ensures high reliability of the self-mode-locking operation, despite the use of a non polarization-maintaining fibers. The single pulse generation regime in all-fibre erbium mode-locking laser based on NPE with a record cavity length of 25 km was demonstrated. Modelocked lasers with such a long cavity have never been studied before. Our result shows a feasibility of stable mode-locked operation even for an ultra-long cavity length. A new design of fibre laser cavity – “y-configuration”, that offers a range of new functionalities for optimization and stabilization of mode-locked lasing regimes was proposed. This novel cavity configuration has been successfully implemented into a long-cavity normal-dispersion self-mode-locked Er-fibre laser. In particular, it features compensation for polarization instability, suppression of ASE, reduction of pulse duration, prevention of in-cavity wave breaking, and stabilization of the lasing wavelength. This laser along with a specially designed double-pass EDFA have allowed us to demonstrate anenvironmentally stable all-fibre laser system able to deliver sub-nanosecond high-energy pulses with low level of ASE noise.

A multiwavelength low-power wavelength-locked slotted Fabry-Perot laser source for WDM applications

Wavelength-locking of a multiwavelength stabilized slotted Fabry-Perot (SFP) laser to a single-mode laser source is experimentally demonstrated. The SFP resonates at channels spaced by similar to 8 nm between 1510 and 1565 nm over a wide range of temperatures and drive currents. Under low-power (<- 20 dBm) external optical injection, wavelength-locking with a sidemode suppression ratio (SMSR) > 25 dB is achieved. A locking width of > 25 GHz and SMSR > 30 dB can be achieved for each locked wavelength channel at injection power > - 16 dBm.

Mode-locked fiber lasers with significant variability of generation regimes

We demonstrate a great variability of single-pulse (with only one pulse/wave-packet traveling along the cavity) generation regimes in fiber lasers passively mode-locked by non-linear polarization evolution (NPE) effect. Combining extensive numerical modeling and experimental studies, we identify multiple very distinct lasing regimes with a rich variety of dynamic behavior and a remarkably broad spread of key parameters (by an order of magnitude and more) of the generated pulses. Such a broad range of variability of possible lasing regimes necessitates developing techniques for control/adjustment of such key pulse parameters as duration, radiation spectrum, and the shape of the auto-correlation function. From a practical view point, availability of pulses/wave-packets with such different characteristics from the same laser makes it imperative to develop variability-aware designs with control techniques and methods to select appropriate application-oriented regimes. © 2014 The Authors.

The framework of the virtual laser tracker - A systematic approach to the assessment of error sources and uncertainty in laser tracker measurement

Laser trackers have been widely used in many industries to meet increasingly high accuracy requirements. In laser tracker measurement, it is complex and difficult to perform an accurate error analysis and uncertainty evaluation. This paper firstly reviews the working principle of single beam laser trackers and state-of- The- Art of key technologies from both industrial and academic efforts, followed by a comprehensive analysis of uncertainty sources. A generic laser tracker modelling method is formulated and the framework of the virtual tracker is proposed. The VLS can be used for measurement planning, measurement accuracy optimization and uncertainty evaluation. The completed virtual laser tracking system should take all the uncertainty sources affecting coordinate measurement into consideration and establish an uncertainty model which will behave in an identical way to the real system. © Springer-Verlag Berlin Heidelberg 2010.

Libs in cultural heritage: recognition and identification of objects in an underwater archaeological shipwreck

Nowadays, one of the most important areas of interest in archeology is the characterization of the submersed cultural heritage. Mediterranean Sea is rich in archaeological findings due to storms, accidents and naval battles since prehistoric times. Chemical analysis of submerged materials is an extremely valuable source of information on the origin and precedence of the wrecks, and also the raw materials employed during the manufacturing of the objects found in these sites. Nevertheless, sometimes it is not possible to extract the archaeological material from the marine environment due to size of the sample, the legislation or preservation purposes. In these cases, the in-situ analysis turns into the only alternative for obtaining information. In spite of this demand, no analytical techniques are available for the in-situ chemical characterization of underwater materials. The versatility of laser-induced breakdown spectroscopy (LIBS) has been successfully tested in oceanography 1. Advantages such as rapid and in situ analysis with no sample preparation make LIBS a suitable alternative for field measurements. To further exploit the inherent advantages of the technology, a mobile fiber-based LIBS platform capable of performing remote measurements up to 50 meters range has been designed for the recognition and identification of artworks in underwater archaeological shipwrecks. The LIBS prototype featured both single-pulse (SP-LIBS) and multi-pulse excitation (MP-LIBS) 2. The use of multi-pulse excitation allowed an increased laser beam energy (up to 95 mJ) transmitted through the optical fiber. This excitation mode results in an improved performance of the equipment in terms of extended range of analysis (to a depth of 50 m) and a broader variety of samples to be analyzed (i.e., rocks, marble, ceramics and concrete). In the present work, the design and construction considerations of the instrument are reported and its performance is discussed on the basis of the spectral response, the remote irradiance achieved upon the range of analysis and its influence on plasma properties, as well as the effect of the laser pulse duration and purge gas to the LIBS signal. Also, to check the reliability and reproducibility of the instrument for field analysis several robustness tests were performed outside the lab. Finally, the capability of this instrument was successfully demonstrated in an underwater archaeological shipwreck (San Pedro de Alcántara, Malaga).

Pt/Nanograined ZnO/SiC Schottky diode based hydrogen and propene sensor

A nanostructured Schottky diode was fabricated to sense hydrogen and propene gases in the concentration range of 0.06% to 1%. The ZnO sensitive layer was deposited on SiC substrate by pulse laser deposition technique. Scanning electron microscopy and X-ray diffraction characterisations revealed presence of wurtzite structured ZnO nanograins grown in the direction of (002) and (004). The nanostructured diode was investigated at optimum operating temperature of 260 °C. At a constant reverse current of 1 mA, the voltage shifts towards 1% hydrogen and 1% propene were measured as 173.3 mV and 191.8 mV, respectively.

Control of dc capacitor voltages in diode-clamped multilevel inverter using bidirectional buck-boost choppers

The dc capacitors voltage unbalancing is the main technical drawback of a diode-clamped multilevel inverter (DCMLI), with more than three levels. A voltage-balancing circuit based on buck–boost chopper connected to the dc link of DCMLI is a reliable and robust solution to this problem. This study presents four different schemes for controlling the chopper circuit to achieve the capacitor voltages equalisation. These can be broadly categorised as single-pulse, multi-pulse and hysteresis band current control schemes. The single-pulse scheme does not involve faster switching actions but need the chopper devices to be rated for higher current. The chopper devices current rating can be kept limited by using the multi-pulse scheme but it involves faster switching actions and slower response. The hysteresis band current control scheme offers faster dynamics, lower current rating of the chopper devices and can nullify the initial voltage imbalance as well. However, it involves much faster switching actions which may not be feasible for some of its applications. Therefore depending on the system requirements and ratings, one of these schemes may be used. The performance and validity of the proposed schemes are confirmed through both simulation and experimental investigations on a prototype five-level diode-clamped inverter.

Ignition delay studies on hydrocarbon fuel with and without additives

Single pulse shock tube facility has been developed in the High Temperature Chemical Kinetics Lab, Aerospace Engineering Department, to carry out ignition delay studies and spectroscopic investigations of hydrocarbon fuels. Our main emphasis is on measuring ignition delay through pressure rise and by monitoring CH emission for various jet fuels and finding suitable additives for reducing the delay. Initially the shock tube was tested and calibrated by measuring the ignition delay of C2H6-O2 mixture. The results are in good agreement with earlier published works. Ignition times of exo-tetrahdyrodicyclopentadiene (C10H16), which is a leading candidate fuel for scramjet propulsion has been studied in the reflected shock region in the temperature range 1250 - 1750 K with and without adding Triethylamine (TEA). Addition of TEA results in substantial reduction of ignition delay of C10H16.

Circular dichroism and 13C nuclear magnetic resonance spectroscopy of pennisetin from pearl millet

The conformation and stability of pearl millet prolamin (pennisetin) were examined by using circular dichroism and C-13 nuclear magnetic resonance spectroscopy. The far UV spectrum of pennisetin in 70% (v/v) aqueous ethanol showed the presence of predominant alpha-helical structure and its occurrence in the alpha + beta class of protein. The far and near UV spectra of pennisetin in ethanol: trifluoroethanol also supported this observation. However pennisetin showed the presence of some helical structure in 8 M urea which is known to be a highly unordered structure forming solvent. A decrease in alpha helical content of native pennisetin was observed with rise in temperature from 5-75-degrees-C and this effect of temperature was found to be reversible. A C-13 NMR spectrum of pennisetin in 70% ethanol suggested a high degree of molecular mobility in ethanol. Comparison of the cross polarization spectrum with the single pulse excitation spectrum suggested pennisetin to be a heterogeneous protein.

Wavelength/Time orthogonal codes with FEC offer dual advantage

To meet the growing demands of the high data rate applications, suitable asynchronous schemes such as Fiber-Optic Code Division Multiple Access (FO-CDMA) are required in the last mile. FO-CDMA scheme offers potential benefits and at the same time it faces many challenges. Wavelength/Time (W/T) 2-D codes for use in FO-CDMA, can be classified mainly into two types: 1) hybrid codes and 2) matrix codes, to reduce the 'time' like property, have been proposed. W/T single-pulse-per-row (SPR) are energy efficient codes as this family of codes have autocorrelation sidelobes of '0', which is unique to this family and the important feature of the W/T multiple-pulses-per-row (MPR) codes is that the aspect ratio can be varied by trade off between wavelength and temporal lengths. These W/T codes have improved cardinality and spectral efficiency over other W/T codes and at the same time have lowest crosscorrelation values. In this paper, we analyze the performances of the FO-CDMA networks using W/T SPR codes and W/T MPR codes, with and without forward error correction (FEC) coding and show that with FEC there is dual advantage of error correction and reduced spread sequence length.

Pulsed radio emission from the Fermi-LAT pulsar J1732-3131: Search and a possible detection at 34.5 MHz

We report our search for and a possible detection of periodic radio pulses at 34.5 MHz from the Fermi Large Area Telescope pulsar J1732-3131. The candidate detection has been possible in only one of the many sessions of observations made with the low-frequency array at Gauribidanur, India, when the otherwise radio weak pulsar may have apparently brightened many folds. The candidate dispersion measure along the sight line, based on the broad periodic profiles from �20min of data, is estimated to be 15.44 ± 0.32 pccc -1. We present the details of our periodic and single-pulse search, and discuss the results and their implications relevant to both, the pulsar and the intervening medium. © 2012 RAS.

Comparison of performance of OCDMA networks with correlation and chiplevel receivers

In this paper optical code-division multiple-access (O-CDMA) packet network is considered, which offers inherent security in the access networks. Two types of random access protocols are proposed for packet transmission. In protocol 1, all distinct codes and in protocol 2, distinct codes as well as shifted versions of all these codes are used. O-CDMA network performance using optical orthogonal codes (OOCs) 1-D and two-dimensional (2-D) wavelength/time single-pulse-per-row (W/T SPR) codes are analyzed. The main advantage of using 2-D codes instead of one-dimensional (1-D) codes is to reduce the errors due to multiple access interference among different users. In this paper, correlation receiver and chip-level receiver are considered in the analysis. Using analytical model, we compute packet-success probability, throughput and compare for OOC and SPR codes in an O-CDMA network and the analysis shows improved performance with SPR codes as compared to OOC codes.