Sensitivity enhancement by increasing the nonlinear crystal length in second-order autocorrelators for ultrashort laser pulses measurement

A theoretical model for interferometric autocorrelation with long nonlinear crystal (input depleted) has been developed and applied to the measurement of the duration of ultrashort pulses. The phase-matching condition is assumed throughout pulse spectrum. The interferometric autocorrelation trace of a mode-locked fibre laser (20 nJ energy, 100 kW peak power, centred at 1595 nm) has been measured by employing a fibre interferometer to avoid misalignment effects and a BBO nonlinear crystal as long as 2 mm, in order to generate higher second-harmonic power. BBO crystal was used because it can keep the phase-matching condition throughout a wide spectrum around 1600 nm. By fitting the experimental measurements and computing according to the theoretical model exposed, it has been demonstrated that the autocorrelator sensitivity is clearly enhanced by increasing the nonlinear crystal length. A temporal duration of 0.18 ps has been obtained by fitting theoretical and experimental values

Measurement method of optical properties of ex vivo biological tissues of rats in the near-infrared range

An optical fiber-based supercontinuum setup and a custom-made spectrophotometer that can measure spectra from 1100 to 2300 nm, are used to describe attenuation properties from different ex vivo rat tissues. Our method is able to differentiate between scattering and absorption coefficients in biological tissues. Theoretical assumptions combined with experimental measurements demonstrate that, in this infrared range, tissue attenuation and absorption can be accurately measured, and scattering can be described as the difference between both magnitudes. Attenuation, absorption, and scattering spectral coefficients of heart, brain, spleen, retina, and kidney are given by applying these theoretical and experimental methods. Light through these tissues is affected by high scattering, resulting in multiple absorption events, and longer wavelengths should be used to obtain lower attenuation values. It can be observed that the absorption coefficient has a similar behavior in the samples under study, with two main zones of absorption due to the water absorption bands at 1450 and 1950 nm, and with different absolute absorption values depending on the constituents of each tissue. The scattering coefficient can be determined, showing slight differences between retina and brain samples, and among heart, spleen and kidney tissues

TRY plant trait database – enhanced coverage and open access

Plant traits—the morphological, anatomical, physiological, biochemical and phenological characteristics of plants—determine how plants respond to environmental factors, affect other trophic levels, and influence ecosystem properties and their benefits and detriments to people. Plant trait data thus represent the basis for a vast area of research spanning from evolutionary biology, community and functional ecology, to biodiversity conservation, ecosystem and landscape management, restoration, biogeography and earth system modelling. Since its foundation in 2007, the TRY database of plant traits has grown continuously. It now provides unprecedented data coverage under an open access data policy and is the main plant trait database used by the research community worldwide. Increasingly, the TRY database also supports new frontiers of trait‐based plant research, including the identification of data gaps and the subsequent mobilization or measurement of new data. To support this development, in this article we evaluate the extent of the trait data compiled in TRY and analyse emerging patterns of data coverage and representativeness. Best species coverage is achieved for categorical traits—almost complete coverage for ‘plant growth form’. However, most traits relevant for ecology and vegetation modelling are characterized by continuous intraspecific variation and trait–environmental relationships. These traits have to be measured on individual plants in their respective environment. Despite unprecedented data coverage, we observe a humbling lack of completeness and representativeness of these continuous traits in many aspects. We, therefore, conclude that reducing data gaps and biases in the TRY database remains a key challenge and requires a coordinated approach to data mobilization and trait measurements. This can only be achieved in collaboration with other initiatives

MATCHING LOCAL COMPOSITION AND MECHANICAL PROPERTY ANISOTROPY OF PREOXIZED (Ni, Pt)Al BOND COATS AFTER THERMAL CYCLING TESTS

Pt-modified nickel aluminide, B2 (Ni,Pt)Al, coatings are used to protect the surface of turbine airfoils against oxidation [1]. However, the lack of ductility of these systems presents a drawback in their performance. At high temperatures several elements diffuse from the superalloy substrate and become incorporated into the B2 phase, which can modify its mechanical properties. This diffusion process also results in a distribution of elements throughout the coating that can change from grain to grain. Few reports on the local, micromechanical properties of B2 (Ni,Pt)Al coatings measured by nanoindentation, taking into account crystal orientation, have been published. No anisotropy effect of elastic modulus in the B2 (Ni,Pt)Al was observed by Durst et al. [2], but their finding remains to be understood, and the effect of local chemical composition is yet to be thoroughly explored. In this work, coupons of Rene-N5 superalloy coated with a B2 (Ni,Pt)Al bond coat were pre-oxidized at different temperatures and oxygen partial pressures (pO2) in order to generate a protective α-Al2O3 scale. An yttria-stabilized zirconia (7YSZ) top-coat layer was subsequently deposited by EB-PVD to complete the thermal barrier coating (TBCs). Finally, the TBCs were subjected to thermal cycling tests, during which the (Ni,Pt)Al was observed to transform from pure B2 to a combination of L10 (martensitic), L12 (ordered fcc), and B2 (ordered bcc) phases. Electron backscattering diffraction (EBSD) was used to identify the crystal orientation of the different phases. The mechanical properties of grains oriented in the [001], [101], and [111] directions were measured by nanoindentation with two different indenter geometries, Berkovich and cono-spherical. No anisotropy of mechanical properties was found using the Berkovich indenter, whereas slight differences were observed with the cono-spherical indenter. Moreover, strong differences in the elastic limit were observed when measuring with the cono-spherical within the same grain, which is attributed to differences in the local chemical composition. Finally, the mechanical properties of the L10 and L12 phases are presented and discussed. References: [1] J. Esslinger and E.E. Affeldt, Transactions of the ASME, Journal of Engineering for Gas Turbines and Power, 121 (1998): 687-690. [2] K. Durst, O. Franke and M. Göken, Proceedings Superalloys (2004): 467-476

FAILURE ANALYSIS OF PRE-OXIDIZED ReneN5/ β-(Ni,Pt)Al/7YSZ EB-PVD THERMAL BARRIER COATINGS

Nowadays Pt-modified nickel aluminides, (Ni,Pt)Al, are highly used as alumina-forming alloys in the aerospace industry. These alloys have been studied to improve the lifetime of the thermal barrier coating systems (TBCs) when they are exposed to thermal-cyclic tests [1-3]. The use of (Ni,Pt)Al alloy as bond coat (BC) is to provide oxidation protection of the Ni-base superalloy (SA) used as a substrate of hot-section turbine blades. BCs act as an aluminum reservoir that leads to the formation of a thermally grown oxide (TGO). The TGO improves the adherence between the metal and a ceramic top coat (TC), which provides thermal insulation during the operation of these components. The aim of the present study is to evaluate the effect of the pre-oxidation treatments before TC deposition on the thermal-cyclic life of ReneN5/(Ni,Pt)Al/7YSZ TBCs. The effect of different oxygen partial pressures (pO2= 2.1x10-1, 1.05x10-1, 1x10-5 and 1x10-9 atm) pre-oxidation treatments were evaluated and compared to regular TBCs after EB-PVD TC deposition in “as-coated” conditions. A post-mortem analysis of the samples was also carried out after 1 h thermal-cyclic testing at 1100ºC to study the intrinsic mechanisms associated to the failure. Samples pre-oxidized with a combination of Argon-Gettered atmosphere (pO2=1x10-9 atm) showed the highest performance in average (1550 cycles to failure). For all the different pre-oxidation conditions, the failure occurred majority along the TC/TGO interface. Mapping of grain orientation determined by EBSD combined with nanoindentation tests were carried out to evaluate anisotropic effects and structural characterization with their mechanical properties after thermal-cyclic tests. Efforts are currently being done to link the failure of the samples to the microstructural characteristics. For instance a continuous layer of martensitic phase, L10, along the bond coat has been observed after failure for the thermal-cyclic tested samples. The reversible L10↔β phase transformation and the reaction β γ' are the main phenomena that take place during thermal cycling and results from the BC aluminum depletion due to TGO formation and its diffusion to the SA [4-6]. Moreover, cracks have been identified in the L10/γ' grains interface. Finally, it must be pointed out that the non-pre-oxidized TBCs have shown a mixed zone in the TGO, which consists on a region where zirconia particles are dispersed in the TGO matrix [7]. References [1] A.G. Evans, et.al., Progress in Materials Science 46 (2001) 505 - 553. [2] V.K. Tolpygo and D.R. Clarke, Surface & Coatings Technology 200 (2005) 1276 - 1281. [3] U. Schulz, et.al., Surface & Coatings Technology 203 (2008) 160 - 170. [4] M.W. Chen, et.al., Acta Materialia (2003), 4279 - 4294. [5] J.L. Smialek and R. Giballa; Metallurgical transactions A (1983), 2143 - 2161. [6] B. Gleeson, W. Wang, S. Hayashi, D.J. Sordelet; Mater Sci Forum 2004. [7] M.J. Stiger, et.al; Metallurgical and Materials Transitions A (2007) Vol.38A 848 - 857

Effect of ternary alloying elements additions on the structural and mechanical properties of B2 NiAl-X intermetallics

NiAl intermetallics have been widely studied due to their interesting properties, such as low density, high melting point, thermal conductivity and most importantly, very good oxidation resistance for structural applications at high temperatures [1]. The B2-NiAl system is a thermodynamically stable, ordered intermetallic that accepts ternary elements additions (e.g. Co, Cr, Mo, Pt, among others) in a wide range of compositions. Since B2-NiAl is a brittle material at low temperature ternary alloying elements additions have been intensively studied. For instance, ductility of B2-NiAl is improved by small additions of Fe, whose strengthening mechanism has been related to preferential deformation along specific slip planes directions [2]. However, a general approach about the effect of alloying elements on the structural stability and mechanical properties (e.g., phase transformations and elastic constants) of B2-NiAl during oxidation remains to be understood. In this work, a set of B2 NiAl-X (X=0, 3, 5, 7, 10, 15 and 34 at% Cr) samples with compositions were processed by high-energy ball milling from Al, Ni and Cr precursor powders. Bulk coupons were obtained by hot pressing (HP) and characterized by X-ray diffraction, scanning electron microscopy and nanoindentation. The superlattice (100), (111), (210) and fundamental (110), (200) and (211) peaks of the binary and ternary B2 phases were observed. The hardness and reduced elastic modulus were determined by nanoindentation. This work was extended on the basis of a theoretical approach to study the stability and elastic-plastic behavior of the B2-phase as a function of Co, Cr, Fe, Mo, and Pt additions in the range of their solubility limits. The theoretical calculations were performed by means of electronic structure first principle calculations of NiAl-X (X=Cr, Fe, Pt, Co, Mo) using the Spin Polarized Relativistic Koringa-Kohn Rostoker (SPRKKR) code. The lattice parameter was obtained by evaluating the calculated total energy of the crystal. The main elastic constants for cubic systems, as well as the bulk modulus were estimated by applying volume-conserving orthorhombic (C11, C12) and monoclinic (C44) deformations of the B2 lattice and fitting the total energy to the Bich-Murnaghan equation of state. The calculations show good agreement between the experimentally determined ordering and elastic-plastic behavior of the B2 phase. [1] Noebe, R.D., Bowman, R.R., and Nathal, M.V., International Materials Reviews, 1993, vol. 38, no 4, p. 193-232. [2] Darolia, R., Larman, D., and Field, R.D., Scripta Metall Mater, 1992, vol. 26, no. 7, p. 1007-101

Search for multimessenger sources of gravitational waves and high-energy neutrinos with Advanced LIGO during its first observing run, ANTARES, and IceCube

Astrophysical sources of gravitational waves, such as binary neutron star and black hole mergers or core-collapse supernovae, can drive relativistic outflows, giving rise to non-thermal high-energy emission. High-energy neutrinos are signatures of such outflows. The detection of gravitational waves and high-energy neutrinos from common sources could help establish the connection between the dynamics of the progenitor and the properties of the outflow. We searched for associated emission of gravitational waves and high-energy neutrinos from astrophysical transients with minimal assumptions using data from Advanced LIGO from its first observing run O1, and data from the Antares and IceCube neutrino observatories from the same time period. We focused on candidate events whose astrophysical origins could not be determined from a single messenger. We found no significant coincident candidate, which we used to constrain the rate density of astrophysical sources dependent on their gravitational-wave and neutrino emission processes

Multi-messenger Observations of a Binary Neutron Star Merger

International audienceOn 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of $\sim 1.7\,{\rm{s}}$ with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg(2) at a luminosity distance of ${40}_{-8}^{+8}$ Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 $\,{M}_{\odot }$. An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at $\sim 40\,{\rm{Mpc}}$) less than 11 hours after the merger by the One-Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over ∼10 days. Following early non-detections, X-ray and radio emission were discovered at the transient’s position $\sim 9$ and $\sim 16$ days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC 4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta

TRY plant trait database, enhanced coverage and open access

Plant traits-the morphological, ahawnatomical, physiological, biochemical and phenological characteristics of plants-determine how plants respond to environmental factors, affect other trophic levels, and influence ecosystem properties and their benefits and detriments to people. Plant trait data thus represent the basis for a vast area of research spanning from evolutionary biology, community and functional ecology, to biodiversity conservation, ecosystem and landscape management, restoration, biogeography and earth system modelling. Since its foundation in 2007, the TRY database of plant traits has grown continuously. It now provides unprecedented data coverage under an open access data policy and is the main plant trait database used by the research community worldwide. Increasingly, the TRY database also supports new frontiers of trait-based plant research, including the identification of data gaps and the subsequent mobilization or measurement of new data. To support this development, in this article we evaluate the extent of the trait data compiled in TRY and analyse emerging patterns of data coverage and representativeness. Best species coverage is achieved for categorical traits-almost complete coverage for 'plant growth form'. However, most traits relevant for ecology and vegetation modelling are characterized by continuous intraspecific variation and trait-environmental relationships. These traits have to be measured on individual plants in their respective environment. Despite unprecedented data coverage, we observe a humbling lack of completeness and representativeness of these continuous traits in many aspects. We, therefore, conclude that reducing data gaps and biases in the TRY database remains a key challenge and requires a coordinated approach to data mobilization and trait measurements. This can only be achieved in collaboration with other initiatives