The multiwavelength variability of 3C 273 Soldi, S.; Türler, M.; Paltani, S. ...
Astronomy and astrophysics (Berlin),
08/2008, Volume:
486, Issue:
2
Journal Article
Peer reviewed
Open access
Aims. We present an update of the 3C 273's database hosted by the ISDC, completed with data from radio to gamma-ray observations over the last 10 years. We use this large data set to study the ...multiwavelength properties of this quasar, especially focussing on its variability behaviour. Methods. We study the amplitude of the variations and the maximum variability time scales across the broad-band spectrum and correlate the light curves in different bands, specifically with the X-rays, to search for possible connections between the emission at different energies. Results. 3C 273 shows variability at all frequencies, with amplitudes and time scales strongly depending on the energy and being the signatures of the different emission mechanisms. The variability properties of the X-ray band imply the presence of either two separate components (possibly a Seyfert-like and a blazar-like) or at least two parameters with distinct timing properties to account for the X-ray emission below and above ~20 keV. The dominant hard X-ray emission is most probably not due to electrons accelerated by the shock waves in the jet as their variability does not correlate with the flaring millimeter emission, but seems to be associated to long-timescale variations in the optical. This optical component is consistent with being optically thin synchrotron radiation from the base of the jet and the hard X-rays would be produced through inverse Compton processes (SSC and/or EC) by the same electron population. We show evidence that this synchrotron component extends from the optical to the near-infrared domain, where it is blended by emission of heated dust that we find to be located within about 1 light-year from the ultraviolet source.
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The growing global concern in relation to the environment and the preservation of non-renewable natural resources has attracted researchers in different areas seeking to develop new eco-friendly ...materials and products based on sustainability principles. In this context, the use of plant fibers and polyurethane derived from castor oil in polymeric composites has been shown to be a good alternative. The aim of this study was to evaluate the influence of the fiber volume fraction, fiber length and alkaline treatment on the mechanical and thermal properties of short random banana fiber reinforced polyurethane derived from castor oil. The banana fibers were chemically modified through contact with 10 wt.% sodium hydroxide solutions for 1 h and characterized through Fourier transformed infrared spectrometry (FTIR), scanning electron microscopy (SEM), tensile strength and density measurements. Through the FTIR spectra and SEM micrographs, modifications in the chemical structure and morphology of the treated fibers were observed compared with untreated fibers. Polymeric composites with different fiber volume fractions and lengths were prepared through the hand lay-up process followed by compression molding at room temperature. The composites were analyzed by SEM, dynamic mechanical analysis (DMA), FTIR spectrometry, tensile strength and pull-out tests. The tensile strength and Young’s modulus increased with increasing fiber volume fraction and length for the untreated and treated banana fiber polyurethane composites. On the other hand, the treated banana fiber composites displayed higher tensile strength and Young’s modulus values than the untreated fiber composites, due to the stronger interfacial interactions between the treated fibers and the polyurethane matrix. These effects occurred due to the morphological and chemical changes in the treated fiber surfaces which promote better adhesion between the fibers and the polyurethane matrix.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The vitrification is a possible treatment for the conditioning of the metallic Long-Lived Intermediate-Level nuclear waste. This process is characterised by the presence of immiscible oxide and ...metallic liquids that react each other. A thermodynamic model using the Calphad method is then required to predict the composition of the treated waste and the speciation of uranium in this complex system. The quaternary Cu-Fe-Si-U is chosen as the most representative to describe the metallic liquids that appear at high temperature. Key sub-systems of this quaternary are experimentally investigated and thermodynamically modelled. The description of the liquidus in the Si-rich corner of the binary Cu-Si is improved. The Cu-U is assessed with the Calphad method for the first time; it is characterised by a large miscibility gap in the liquid phase. Some new ternary isotherms of the ternary Cu-Fe-Si are then proposed: a large liquid miscibility gap appears also in this system in agreement with the observed behaviour of the metallic liquid during the experimental investigations. The Cu-Si-U system is characterised by three ternary intermetallic compounds: CuSiU, Cu2Si2U and Cu4Si4U3. A first description is proposed, but more data are still required to improve the thermodynamic modelling of this system.
•The re-assessment of Cu-Si shows an improvement in the description of the liquidus.•The new Cu-Fe-Si model predicts well the appearance of the liquid miscibility gap.•The first Calphad assessment of Cu-U and Cu-Si-U is proposed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Metal carbenes appended with two electron‐donating groups, known as “donor/donor” carbenes, undergo diastereo‐ and enantioselective rhodium‐catalyzed C−H insertion reactions with ether substrates to ...form benzodihydrofurans. Unlike the reactions of metal carbenes with electron‐withdrawing groups attached, the attenuated electrophilicity enables these reactions to be conducted in Lewis basic solvents (e.g., acetonitrile) and in the presence of water. The diazo precursors for these species are prepared in situ from hydrazone using a mild and chemoselective oxidant (MnO2). Although this sequence often can be performed in one‐pot, control experiments have elucidated why a “two‐pot” process is often more efficient. A thorough screening of achiral catalysts demonstrated that sterically encumbered catalysts are optimal for diastereoselective reactions. Although efficient insertion into allylic and propargylic C−H bonds is observed, competing dipolar cycloaddition processes are noted for some substrates. The full substrate scope of this useful method of benzodihydrofuran synthesis, mechanisms of side reactions, and computational support for the origins of stereoselectivity are described.
Donor/donor metal carbenes undergo diastereo‐ and enantioselective rhodium‐catalyzed C−H insertion reactions to form substituted benzodihydrofurans with high selectivity. Herein, an extensive substrate scope of this useful synthetic method is described, the mechanisms of side reactions is probed, and computational support for the origin of stereoselectivity is provided.
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Aims. Multiwavelength variability of blazars offers indirect, but very effective, insight into their powerful engines and on the mechanisms through which energy is propagated from the centre down the ...jet. The BL Lac object Mkn 421 is a TeV emitter, a bright blazar at all wavelengths, and therefore an excellent target for variability studies. Methods. We activated INTEGRAL observations of Mkn 421 in an active state on 16–21 April 2013, and complemented them with Fermi-LAT data. Results. We obtained well sampled optical, soft, and hard X-ray light curves that show the presence of two flares and time-resolved spectra in the 3.5–60 keV (JEM-X and IBIS/ISGRI) and 0.1–100 GeV (Fermi-LAT) ranges. The average flux in the 20–100 keV range is 9.1 × 10-11 erg s-1 cm-2 (~4.5 mCrab) and the nuclear average apparent magnitude, corrected for Galactic extinction, is V ≃ 12.2. In the time-resolved X-ray spectra, which are described by broken power laws and, marginally better, by log-parabolic laws, we see a hardening that correlates with flux increase, as expected in refreshed energy injections in a population of electrons that later cool via synchrotron radiation. The hardness ratios between the JEM-X fluxes in two different bands and between the JEM-X and IBIS/ISGRI fluxes confirm this trend. During the observation, the variability level increases monotonically from the optical to the hard X-rays, while the large LAT errors do not allow a significant assessment of the MeV-GeV variability. The cross-correlation analysis during the onset of the most prominent flare suggests a monotonically increasing delay of the lower frequency emission with respect to that at higher frequency, with a maximum time-lag of about 70 min, that is however not well constrained. The spectral energy distributions from the optical to the TeV domain were compared to homogeneous models of blazar emission based on synchrotron radiation and synchrotron self-Compton scattering. They represent a satisfactory description, except in the state corresponding to the LAT softest spectrum and highest flux. Conclusions. Multiwavelength variability of Mkn 421 can be very complex, with patterns changing from epoch to epoch down to intra-day timescales, depending on the emission state. This makes accurate monitoring of this source during bright hard X-ray states necessary and calls for the elaboration of multicomponent, multizone, time-dependent models.
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The origin of the iron fluorescent line at 6.4 keV from an extended region surrounding the Arches cluster is debated and the non-variability of this emission up to 2009 has favoured the low-energy ...cosmic ray origin over a possible irradiation by hard X-rays. By probing the variability of the Arches cloud non-thermal emission in the most recent years, including a deep observation in 2012, we intend to discriminate between the two competing scenarios. We perform a spectral fit of XMM–Newton observations collected from 2000 to 2013 in order to build the Arches cloud light curve corresponding to both the neutral Fe Kα line and the X-ray continuum emissions. We reveal a 30 per cent flux drop in 2012, detected with more than 4σ significance for both components. This implies that a large fraction of the studied non-thermal emission is due to the reflection of an X-ray transient source.
The revision of the structure of the sesquiterpene aquatolide from a bicyclo2.2.0hexane to a bicyclo2.1.1hexane structure using compelling NMR data, X-ray crystallography, and the recent ...confirmation via full synthesis exemplify that the achievement of “structural correctness” depends on the completeness of the experimental evidence. Archived FIDs and newly acquired aquatolide spectra demonstrate that archiving and rigorous interpretation of 1D 1H NMR data may enhance the reproducibility of (bio)chemical research and curb the growing trend of structural misassignments. Despite being the most accessible NMR experiment, 1D 1H spectra encode a wealth of information about bonds and molecular geometry that may be fully mined by 1H iterative full spin analysis (HiFSA). Fully characterized 1D 1H spectra are unideterminant for a given structure. The corresponding FIDs may be readily submitted with publications and collected in databases. Proton NMR spectra are indispensable for structural characterization even in conjunction with 2D data. Quantum interaction and linkage tables (QuILTs) are introduced for a more intuitive visualization of 1D J-coupling relationships, NOESY correlations, and heteronuclear experiments. Overall, this study represents a significant contribution to best practices in NMR-based structural analysis and dereplication.
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IJS, KILJ, NUK, PNG, UL, UM
The synthesis and the solution-state self-assembly of the “hybrid” diblock copolymers, maltoheptaose-block-poly(methyl methacrylate) (MH-b-PMMA), into large compound micelles (LCMs) and reverve ...micelle-type nanoparticles, are reported in this paper. The copolymers were self-assembled in water and acetone by direct dissolution method, and the morphologies of the nanoparticles were investigated by dynamic light scattering (DLS), nanoparticle tracking analysis (NTA), transmission electron microscopy (TEM), atomic force microscopy (AFM), proton nuclear magnetic resonance (1H NMR), and fluorescence spectroscopy as a function of the volume fraction of the copolymer hydrophobic block, copolymer concentration, stirring speed, and solvent polarity. The DLS measurements and TEM images showed that the hydrodynamic radius (R h) of the LCMs obtained in water increases with the copolymer concentration. Apart from that, increasing the stirring speed leads to polydispersed aggregations of the LCMs. On the other hand, in acetone, the copolymers self-assembled into reverse micelle-type nanoparticles having R h values of about 6 nm and micellar aggregates, as revealed the results obtained from DLS, AFM, and 1H NMR analyses. The variation in micellar structure, that is, conformational inversion from LCMs to reverse micelle-type structures in response to polarity of the solvent, was investigated by apparent water contact angle (WCA) and 1H NMR analyses. This conformational inversion of the nanoparticles was further confirmed by encapsulation and release of hydrophobic guest molecule, Nile red, characterized by fluorescence spectroscopy.
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The identification of the factors that enable normally folded proteins to remain in their soluble and functional states is crucial for a comprehensive understanding of any biological system. We have ...determined a series of energy landscapes of the acylphosphatase from Drosophila melanogaster under a variety of conditions by combining NMR measurements with restrained molecular dynamics simulations. We thus analyzed the differences in the structures, dynamics, and energy surfaces of the protein in its soluble state or in situations where it aggregates through conformational states that have native-like structure, folding stability, and enzymatic activity. The study identifies the nature of the energy barriers that under normal physiological conditions prevent the protein ensemble from populating dangerous aggregation-prone states. We found that such states, although similar to the native conformation, have altered surface charge distribution, alternative topologies of the β-sheet region, and modified solvent exposure of hydrophobic surfaces and aggregation-prone regions of the sequence. The identified barriers allow the protein to undergo functional dynamics while remaining soluble and without a significant risk of misfolding and aggregation into nonfunctional and potentially toxic species.
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