External Modulation Optical Coherent Domain Reflectometry with Long Measurement Range

Optical coherent domain reflectometry (OCDR) can achieve a high spatial resolution that is independent of the bandwidth of the receiver, but the measurement range is usually very limited. Here we propose an external modulation OCDR system, in which a pair of linear frequency-modulated pulses generated by one modulator are employed as the probe pulse and the reference, respectively. The spatial resolution is determined by the frequency modulation range of the pulse, and the measurement speed is boosted by orders because the proposed technology can simultaneously diagnose a section of fiber with each pair of pulses, while only a single point can be accessed at a time in typical OCDR. In the demonstrational experiment, a measurement range of up to 50 km is achieved with a spatial resolution of 1.4 m and a measuring time of less than 30 s.

Carbide-Derived Carbons: WAXS and Raman Spectra for Detailed Structural Analysis

Quick characterization methods to determine the structure of carbon materials are sought after for a wide array of technical applications. In this study we present the combined analysis of the structure of carbide-derived carbons (CDCs) with Raman spectroscopy and wide-angle X-ray scattering (WAXS) methods. We present the optimal deconvolution method to be used for the detailed analysis of Raman spectroscopy data of CDCs and comparison to corresponding WAXS results is made. For a broad set of CDCs both WAXS and Raman spectroscopy data showed that the average graphene layer extent increases with synthesis temperature of CDC, while the coherent domain lengths obtained from Raman spectroscopy higher by an average of 4.4 nm. In addition, the presence of correlations between the parameters (D-band width and the parameter A∑D/A∑G) from Raman spectroscopy and the synthesis temperature are established. Based on the WAXS and Raman spectra data analysis the strong influence of the precursor carbide structure on the graphitization pathway is shown.

Superconducting properties of very high quality NbN thin films grown by pulsed laser deposition

In this work, we study the effect of the various substrates on the growth and superconducting properties of NbN thin films grown by using pulsed laser ablation in a N2 + 1%H2 atmosphere on MgO, Al2O3 and Si substrates. Structural and superconducting analyses of the films demonstrate that using MgO and Al2O3 substrates can significantly improve the film properties compared to Si substrate. The X-ray diffraction data indicate that MgO and Al2O3 substrates produce highly oriented superconducting NbN films with large coherent domain size in the out-of plane direction on the order of layer thickness and with a superconducting transition temperature of 13.1 K and 15.2 K, respectively. On the other hand, the NbN film grown on the Si substrate exhibits random polycrystalline orientation. Together with the smallest coherent domain size it leads to the lower critical temperature of 8.3 K. Finally, by using a passivation surface layer we are able to improve superconducting properties of NbN thin film and we observe superconducting transition temperature 16.6 K, the one of the highest value reported so far for 50 nm thick NbN film on sapphire.

Combined texture and microstructure analysis of deformed crystals by high-energy X-ray diffraction

It is shown that high-energy X-ray diffraction allows a fast and accurate texture and microstructure analysis of crystals, which can help to set up optimal industrial procedures for materials manufacturing. This paper presents the experimental and theoretical aspects of quantitative texture analysis using high-energy synchrotron beams. Intensity corrections are less important in this approach than in classical laboratory methods; however, the most important correction, related to the Lorentz factor, can introduce relative fraction changes of up to about 40% compared to the uncorrected case. The resolution of the orientation density function also influences the results. For example, the usual 5° resolution leads to relative deviations of up to 30% in the fraction of some components. The method allowed detection of small changes taking place during the recovery and continuous recrystallization of a cold-rolled Al–TiB2 nanocomposite. Texture information was combined with the results of line profile analysis, evidencing the evolution of the average dislocation density and coherent domain size of the selected grain families. It was found that recovery, as described in terms of dislocation annihilation and coherent domain coarsening, takes place at similar rates in all components.

Approach to equilibrium of a quantum system and generalization of the Montroll–Shuler equation for vibrational relaxation of a molecular oscillator

The approach to equilibrium of a quantum mechanical system in interaction with a bath is studied from a practical as well as a conceptual point of view. Explicit memory functions are derived for given models of bath couplings. If the system is a harmonic oscillator representing a molecule in interaction with a reservoir, the generalized master equation derived becomes an extension into the coherent domain of the well-known Montroll–Shuler equation for vibrational relaxation and unimolecular dissociation. A generalization of the Bethe–Teller result regarding energy relaxation is found for short times. The theory has obvious applications to relaxation dynamics at ultra-short times as in observations on the femtosecond time scale and to the investigation of quantum coherence at those short times. While vibrational relaxation in chemical physics is a primary target of the study, another system of interest in condensed matter physics, an electron or hole in a lattice subjected to a strong DC electric field that gives rise to well-known Wannier–Stark ladders, is naturally addressed with the theory. Specific system–bath interactions are explored to obtain explicit details of the dynamics. General phenomenological descriptions of the reservoir are considered rather than specific microscopic realizations.

Microstructure and Residual Stress in T40 Titanium after Tensile Test

The goal work of this work is to describe the qualitative and quantitative behaviour of titanium T40 during tensile test. Material characteristics were determined using EBSD and X-ray techniques. Textures, twin boundary fractions, residual stresses and coherent domain size were determined. It was found that deformation mechanisms and microstructure characteristics are different in the samples stretched along rolling and transverse directions. For example the average grain size, as determined from EBSD measurements, is higher in the sample stretched along rolling direction. Also smaller coherent domains form and residual stress is more easily relaxed in this sample. A strong appearance of tensile twins was observed in the samples deformed along transverse direction. In the present paper a complex study of material characteristics and deformation mechanisms is presented. A special emphasis is done on residual stress characteristics determined in the samples stretched in two perpendicular directions.