Chemical sensor using Mach-Zehnder interferometer based on a pair of largely tilted fiber gratings

We propose an in-fiber Mach-Zehnder interferometer formed by a pair of largely tilted fiber gratings. The interference spectral characteristics have been investigated. The experimental results using this device as a chemical sensor have a sensitivity as high as 719nm/RIU. © 2012 OSA.

On the theory of the modulation instability in optical fiber and laser amplifiers

The modulation instability (MI) in optical fiber amplifiers and lasers with anomalous dispersion leads to CW beam breakup and the growth of multiple pulses. This can be both a detrimental effect, limiting the performance of amplifiers, and also an underlying physical mechanism in the operation of MI-based devices. Here we revisit the analytical theory of MI in fiber optical amplifiers. The results of the exact theory are compared with the previously used adiabatic approximation model, and the range of applicability of the latter is determined. The same technique is applicable to the study of spatial MI in solid state laser amplifiers and MI in non-uniform media. © 2011 SPIE.

Orthogonally polarized bright–dark pulse pair generation in mode-locked fiber laser with a large-angle tilted fiber grating

We report on the generation of orthogonally polarized bright–dark pulse pair in a passively mode-locked fiber laser with a large-angle tilted fiber grating (LA-TFG). The unique polarization properties of the LA-TFG, i.e., polarization-dependent loss and polarization-mode splitting, enable dual-wavelength mode-locking operation. Besides dual-wavelength bright pulses with uniform polarization at two different wavelengths, the bright–dark pulse pair has also been achieved. It is found that the bright–dark pulse pair is formed due to the nonlinear couplings between lights with two orthogonal polarizations and two different wavelengths. Furthermore, harmonic mode-locking of bright–dark pulse pair has been observed. The obtained bright–dark pulse pair could find potential use in secure communication system. It also paves the way to manipulate the generation of dark pulse in terms of wavelength and polarization, using specially designed fiber grating for mode-locking.

On the theory of the modulation instability in optical fiber amplifiers

The modulation instability (MI) in optical fiber amplifiers and lasers with anomalous dispersion leads to cw radiation breakup. This can be both a detrimental effect limiting the performance of amplifiers and an underlying physical mechanism in the operation of MI-based devices. Here we revisit the analytical theory of MI in fiber optical amplifiers. The results of the exact theory are compared with the previously used adiabatic approximation model, and the range of applicability of the latter is determined. © 2010 Optical Society of America.

In-cavity pulse shaping and dissipative parametric instability mode-locking in fibre lasers

At the level of fundamental research, fibre lasers provide convenient and reproducible experimental settings for the study of a variety of nonlinear dynamical processes, while at the applied research level, pulses with different and optimised features – e.g., in terms of pulse duration, temporal and/or spectral shape, energy, repetition rate and emission bandwidth – are sought with the general constraint of developing efficient cavity architectures. In this work, we review our recent progress on the realisation of pulse shaping in passively- mode-locked fibre lasers by inclusion of an amplitude and phase spectral filter into the laser cavity. We present a fibre laser design in which pulse shaping occurs through filtering of a spectrally nonlinearly broadened pulse in the cavity. This strategy of pulse shaping is illustrated through the numerical demonstration of the laser operation in different pulse-generation regimes, including parabolic, flattop and triangular waveform generations, depending on the amplitude profile of the in-cavity spectral filter [1]. As an application of this general approach, we show that the use of an in-cavity flat-top spectral filter makes it possible to directly generate sinc-shaped Nyquist pulses of high quality and of a widely tunable bandwidth from the laser [2]. We also report on a recently-developed versatile erbium-doped fibre laser, in which conventional soliton, dispersion-managed soliton (stretched-pulse) and dissipative soliton mode-locking regimes can be selectively and reliably targeted by programming different group-velocity dispersion profiles and bandwidths on an in-cavity programmable filter [3]. Further, we report on our recent results on the passive mode locking of a Raman fibre laser by a recently predicted new type of parametric instability – the dissipative Faraday instability [4], where spatially periodic zig-zag modulation of spectrally dependent losses can lead to pattern formation in the temporal domain. High-order harmonic mode locking is achieved in a very simple experimental configuration, with the laser cavity including an optical fibre and two chirped fibre Bragg gratings, and no additional mode-locking elements. The results not only open up new possibilities for the design of mode-locked lasers, but extend beyond fibre optics to other fields of physics and engineering. References [1] S. Boscolo, C. Finot, H. Karakuzu, P. Petropoulos, “Pulse shaping in mode-locked fiber laser by in-cavity spectral filter,” Opt. Lett., vol. 39, pp. 438–441, 2014. [2] S. Boscolo, C. Finot, S. K. Turitsyn, “Bandwidth programmable optical Nyquist pulse generation in passively mode-locked fiber laser,” IEEE Photon. J., vol. 7, 7802008(8), 2015. [3] J. Peng, S. Boscolo, “Filter-based dispersion-managed versatile ultrafast fibre laser,” Sci. Rep., 2016, In press. [4] A. M. Perego, N. Tarasov, D. V. Churkin, S. K. Turitsyn, K. Staliunas, “Pattern generation by dissipative parametric instability,” Phys. Rev. Lett., vol. 116, 028701, 2016.

Consistency of the decision-maker in pair-wise comparisons

Most authors assume that the natural behaviour of the decision-maker is being inconsistent. This paper investigates the main sources of inconsistency and analyses methods for reducing or eliminating inconsistency. Decision support systems can contain interactive modules for that purpose. In a system with consistency control, there are three stages. First, consistency should be checked: a consistency measure is needed. Secondly, approval or rejection has to be decided: a threshold value of inconsistency measure is needed. Finally, if inconsistency is ‘high’, corrections have to be made: an inconsistency reducing method is needed. This paper reviews the difficulties in all stages. An entirely different approach is to elaborate a decision support system in order to force the decision-maker to give consistent values in each step of answering pair-wise comparison questions. An interactive questioning procedure resulting in consistent (sub) matrices has been demonstrated.

Comparison of ion pair and buffered mobile phase chromatography of haloacetic acids using direct and indirect UV and fluorescence detection

Reversed-phase high performance liquid chromatographic methods for the analysis of Haloacetic acids have been developed and compared to conventional direct detection methods. Haloacetic acids commonly found in drinking water, including monochloro-, dichloro-, bromo-, iodo- and trichloroacetic acids- have been studied. The ion pairing agent benzyltributylammonium ion was studied in detail using indirect UV and indirect fluorescence detection. Five different competing ions were evaluated to decrease analysis times and lower the detection limit by this new method. The direct detection method utilized an ammonium sulfate buffer and UV detection yielding a detection limit of 100 ppb. The indirect method developed has the advantage of being able to simultaneously analyze UV and non-UV absorbing ions and molecules but requires long equilibration times and demonstrated lower sensitivity than the direct method. ^

Essays on the determinants of private investment: The effects of relative price uncertainty and political instability

The objective of this study was to provide empirical evidence on the effects of relative price uncertainty and political instability on private investment. My effort is expressed in a single-equation model using macroeconomic and socio-political data from eight Latin American countries for the period 1970–1996. Relative price uncertainty is measured by the implied volatility of the exchange rate and political instability is measured by using indicators of social unrest and political violence. ^ I found that, after controlling for other variables, relative price uncertainty and political instability are negatively associated with private investment. Macroeconomic and political stability are key ingredients for the achievement of a strong investment response. This highlights the need to develop the state and build a civil society in which citizens can participate in decision-making and express consent without generating social turmoil. At the same time the government needs to implement structural policies along with relative price adjustments to eliminate excess volatility in price movements in order to provide a stable environment for investment. ^

Instability of CTG Repeats is Governed by the Position of a DNA Base Lesion through Base Excision Repair

Trinucleotide repeat (TNR) expansions and deletions are associated with human neurodegeneration and cancer. However, their underlying mechanisms remain to be elucidated. Recent studies have demonstrated that CAG repeat expansions can be initiated by oxidative DNA base damage and fulfilled by base excision repair (BER), suggesting active roles for oxidative DNA damage and BER in TNR instability. Here, we provide the first evidence that oxidative DNA damage can induce CTG repeat deletions along with limited expansions in human cells. Biochemical characterization of BER in the context of (CTG)20 repeats further revealed that repeat instability correlated with the position of a base lesion in the repeat tract. A lesion located at the 59-end of CTG repeats resulted in expansion, whereas a lesion located either in the middle or the 39-end of the repeats led to deletions only. The positioning effects appeared to be determined by the formation of hairpins at various locations on the template and the damaged strands that were bypassed by DNA polymerase b and processed by flap endonuclease 1 with different efficiency. Our study indicates that the position of a DNA base lesion governs whether TNR is expanded or deleted through BER.

Novos protocolos teóricos utilizados nos estudos das ligações hidrogênio-hidrogênio, na estabilidade do tetraedrano, seus derivados e das reações de diels-alder e na quantificação da afinidade de fármacos

This thesis was performed in four chapters, at the theoretical level, focused mainly on electronic density. In the first chapter, we have applied an undergraduate minicourse of Diels-Alder reaction in Federal University of Rio Grande do Norte. By using computational chemistry tools students could build the knowledge by themselves and they could associate important aspects of physical-chemistry with Organic Chemistry. In the second chapter, we studied a new type of chemical bond between a pair of identical or similar hydrogen atoms that are close to electrical neutrality, known as hydrogen-hydrogen (H-H) bond. In this study performed with complexed alkanes, provides new and important information about their stability involving this type of interaction. We show that the H-H bond playing a secondary role in the stability of branched alkanes in comparison with linear or less branched isomers. In the third chapter, we study the electronic structure and the stability of tetrahedrane, substituted tetrahedranes and silicon and germanium parents, it was evaluated the substituent effect on the carbon cage in the tetrahedrane derivatives and the results indicate that stronger electron withdrawing groups (EWG) makes the tetrahedrane cage slightly unstable while slight EWG causes a greater instability in the tetrahedrane cage. We showed that the sigma aromaticity EWG and electron donating groups (EDG) results in decrease and increase, respectively, of NICS and D3BIA aromaticity indices. In addition, another factor can be utilized to explain the stability of tetra-tert-butyltetrahedrane as well as HH bond. GVB and ADMP were also used to explain the stability effect of the substituents bonded to the carbon of the tetrahedrane cage. In the fourth chapter, we performed a theoretical investigation of the inhibitory effect of the drug abiraterone (ABE), used in the prostate cancer treatment as CYP17 inhibitor, comparing the interaction energies and electron density of the ABE with the natural substrate, pregnenolone (PREG). Molecular dynamics and docking were used to obtain the CYP1ABE and CYP17-PREG complexes. From molecular dynamics was obtained that the ABE has higher diffusion trend water CYP17 binding site compared to the PREG. With the ONIOM (B3LYP:AMBER) method, we find that the interaction electronic energy of ABE is 21.38 kcal mol-1 more stable than PREG. The results obtained by QTAIM indicate that such stability is due a higher electronic density of interactions between ABE and CYP17

PCNA Retention on DNA into G2/M Phase Causes Genome Instability in Cells Lacking Elg1

Open Access funded by Medical Research Council Acknowledgments We thank Richard Kolodner, Grant Brown, and Daniel Durocher for strains and plasmids. We thank Anne Donaldson, Alexander Lorenz, and Shin-ichiro Hiraga from University of Aberdeen for careful reading of the manuscript. Research in T.K.’s lab is supported by Medical Research Council Career Development Fellowship L019698/1. V.K.G. was supported by Biotechnology and Biological Sciences Research Council grant K006304/1. T.S.T. was supported by grants from the Ministry of Education, Culture, Sports, Science and Technology of Japan (nos. 23131507 and 25131712).

Double decomposition : decomposing the variance in subcomponents of male extra-pair reproductive success

Peer reviewed

Double decomposition : decomposing the variance in subcomponents of male extra-pair reproductive success

Peer reviewed

Internal instability as a possible failure mechanism for layered composites

Funding Financial support of part of this research by The Royal Society, The Royal Society of Edinburgh, The Royal Academy of Engineering and The Carnegie Trust for the Universities of Scotland is gratefully acknowledged.