Context. Attenuation of the TeV γ-ray flux from distant blazars through pair production with extragalactic background light leads to the development of electromagnetic cascades and subsequent, lower ...energy, GeV secondary γ-ray emission. Due to the deflection of VHE cascade electrons by extragalactic magnetic fields (EGMF), the spectral shape of this arriving cascade γ-ray emission is dependent on the strength of the EGMF. Thus, the spectral shape of the GeV–TeV emission from blazars has the potential to probe the EGMF strength along the line of sight to the object. Constraints on the EGMF previously derived from the gamma-ray data suffer from an uncertainty related to the non-simultaneity of GeV and TeV band observations. Aims. We investigate constraints on the EGMF derived from observations of blazars for which TeV observations simultaneous with those by Fermi telescope were reported. We study the dependence of the EGMF bound on the hidden assumptions it rests upon. Methods. We select blazar objects for which simultaneous Fermi/LAT GeV and Veritas, MAGIC or HESS TeV emission have been published. We model the development of electromagnetic cascades along the gamma-ray beams from these sources using Monte Carlo simulations, including the calculation of the temporal delay incurred by cascade photons, relative to the light propagation time of direct γ-rays from the source. Results. Constraints on the EGMF could be derived from the simultaneous GeV–TeV data on the blazars RGB J0710+591, 1ES 0229+200, and 1ES 1218+304. The measured source flux level in the GeV band is lower than the flux of the expected cascade component calculated under the assumption of zero EGMF. Assuming that the reason for the suppression of the cascade component is the extended nature of the cascade emission, we find that B ≳ 10-15 G (assuming an EGMF correlation length of ≥1 Mpc) is consistent with the data. Alternatively, the assumption that the suppression of the cascade emission is caused by the time delay of the cascade photons the data are consistent with B ≳ 10-17 G for the same correlation length.
Rare earth oxides have seen increased usage over the years in batteries and catalysts. Due to their unique electronic properties, they are the subject of fundamental and practical interest. However, ...the complexity in their electronic structures makes unambiguous characterization, such as X-ray photoelectron spectroscopy (XPS), very challenging. Lanthanum oxide (La
O
) has attracted special attention as a promising catalyst for the oxidative coupling of methane (OCM) reaction. In this work, a new and reliable way of XPS calibration is developed by applying various in situ preparations for a nanorod La
O
catalyst to intentionally form different lanthanum compounds, followed by XPS characterization and corroboration with first principles calculations. To form different compounds, five sample treatments were performed including heating in vacuum and treatment with O
, CH
, CO
, and H
O, which are all relevant to OCM reaction conditions. Adventitious carbon or lattice oxygen, as conventional calibration standard species for energy scale, is only suitable for one or few in situ prepared surfaces. Our results also clearly demonstrate the vital difference between performing the ex situ analysis after exposure of the sample to the atmosphere and the in situ analysis. By carefully comparing the spectra of various photoemission peaks of different compounds, we conclude that the binding energy of 102.2 eV for the La 4d
peak can be used as the internal calibration standard for all considered samples. Furthermore, different oxygen species were unambiguously identified by matching the oxygen 1s binding energies from the in situ measurements and first principles predictions.
The method of X-ray photoelectron spectroscopy was used to study the interaction of the model Pt/TiO2 catalysts with NO2 and the following reduction of the oxidized Pt nanoparticles in vacuum, ...hydrogen, and methane. It was shown that, while interacting with NO2 at room temperature, the metal Pt nanoparticles transform, first, into the phase which was tentatively assigned as particles containing subsurface/dissolved oxygen Pt-Osub, and then, into the PtO and PtO2 oxides. If only the first state of platinum Pt-Osub is formed, it demonstrates exclusively high reactivity toward hydrogen. For the samples containing simultaneously Pt-Osub, PtO, and PtO2, the highest reaction ability was demonstrated by PtO2; contrary to the other two oxidized states, it is reducing while kept in vacuum under X-ray irradiation. All three coexisting states of the oxidized platinum can be reduced when heated in vacuum as well as while interacting with hydrogen at room temperature. First, PtO2 is reduced to PtO. PtO and Pt-Osub begin being reduced after the complete consumption of PtO2. We propose that, when a sample contains simultaneously all three states of oxidized platinum, the supported particles have a core–shell structure with a nucleus of perturbed platinum containing oxygen atoms, which are covered with a film of Pt oxides. It was shown that none of the oxidized states of platinum react with methane at room temperature.
Automated docking is one of the most important tools for structure‐based drug design that allows prediction of ligand binding poses and also provides an estimate of how well small molecules fit in ...the binding site of a protein. A new scoring function based on AutoDock and AutoDock Vina has been introduced. The new hybrid scoring function is a linear combination of the two scoring function components derived from a multiple linear regression fitting procedure. The scoring function was built on a training set of 2412 protein–ligand complexes from pdbbind database (www.pdbbind.org.cn, version 2012). A test set of 313 complexes that appeared in the 2013 version was used for validation purposes. The new hybrid scoring function performed better than the original functions, both on training and test sets of protein–ligand complexes, as measured by the non‐parametric Pearson correlation coefficient, R, mean absolute error (MAE), and root‐mean‐square error (RMSE) between the experimental binding affinities and the docking scores. The function also gave one of the best results among more than 20 scoring functions tested on the core set of the pdbbind database. The new AutoDock hybrid scoring function will be implemented in modified version of AutoDock.
A new scoring function was built on a training set of 2412 protein–ligand complexes from the pdbbind database. A test set of 313 complexes that appeared in the 2013 version of the database was used for validation purposes. The new hybrid scoring function performed better than the original functions and gave one of the best results among more than 20 scoring functions tested on the core set of the pdbbind database.
The direct conversion of carbon dioxide (CO2) using green hydrogen is a sustainable approach to jet fuel production. However, achieving a high level of performance remains a formidable challenge due ...to the inertness of CO2 and its low activity for subsequent C–C bond formation. In this study, we prepared a Na-modified CoFe alloy catalyst using layered double-hydroxide precursors that directly transforms CO2 to a jet fuel composed of C8–C16 jet-fuel-range hydrocarbons with very high selectivity. At a temperature of 240°C and pressure of 3 MPa, the catalyst achieves an unprecedentedly high C8–C16 selectivity of 63.5% with 10.2% CO2 conversion and a low combined selectivity of less than 22% toward undesired CO and CH4. Spectroscopic and computational studies show that the promotion of the coupling reaction between the carbon species and inhibition of the undesired CO2 methanation occur mainly due to the utilization of the CoFe alloy structure and addition of the Na promoter. This study provides a viable technique for the highly selective synthesis of eco-friendly and carbon-neutral jet fuel from CO2.
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•An alloy is developed for the direct CO2 hydrogenation to jet-fuel-range hydrocarbons•The selectivity of the hydrocarbons (63.5%) exceeds the theoretical maximum value•The CoFe alloy is the active phase in the coupling reaction between surface carbons•The CoFe alloy is a highly efficient catalyst in the presence of a sodium promoter
Context. The increase in sensitivity of Imaging Atmospheric Cherenkov Telescopes (IACTs) has lead to numerous detections of extended γ-ray sources at TeV energies, sometimes of sizes comparable to ...the instrument’s field of view. This creates a demand for advanced and flexible data analysis methods that are able to extract source information using the photon counts in the entire field of view. Aims. We present a new software package, “SkyPrism”, aimed at performing 2D (3D if energy is considered) fits of IACT data that possibly contain multiple and extended sources. The fits are based on sky images binned in energy. Although the development of this package was focused on the analysis of data collected with the MAGIC telescopes, it can further be adapted to other instruments, such as the future Cherenkov Telescope Array. Methods. We have developed a set of tools that in addition to sky images (count maps) compute the instrument response functions of MAGIC (effective exposure throughout the field of view, point spread function, energy resolution, and background shape) based on the input data, Monte Carlo simulations, and the pointing track of the telescopes. With this information, the package can perform a simultaneous maximum likelihood fit of source models of arbitrary morphology to the sky images providing energy spectra, detection significances, and upper limits. Results. We demonstrate that the SkyPrism tool accurately reconstructs the MAGIC point spread function, on- and off-axis performance as well as the underlying background. We further show that for a point source analysis with the MAGIC default observational settings, SkyPrism gives results compatible with those of the standard tools while being more flexible and widely applicable.
A thermodynamically unstable spin glass growth model described by means of the parametrically-dependent Kardar-Parisi-Zhang equation is analyzed within the symplectic geometry-based ...gradient-holonomic and optimal control motivated algorithms. The finitely-parametric functional extensions of the model are studied, and the existence of conservation laws and the related Hamiltonian structure is stated. A relationship of the Kardar-Parisi-Zhang equation to a so called dark type class of integrable dynamical systems, on functional manifolds with hidden symmetries, is stated.
Context. The imaging and timing properties of γ-ray emission from electromagnetic cascades initiated by very-high-energy (VHE) γ-rays in the intergalactic medium depend on the strength B and ...correlation length λB of intergalactic magnetic fields (IGMF). Aims. We study the possibility of measuring both B and λB via observations of the cascade emission with γ-ray telescopes. Methods. For each measurement method, we find two characteristics of the cascade signal, which are sensitive to the IGMF B and λB values in different combinations. For the case of IGMF measurement using the observation of extended emission around extragalactic VHE γ-ray sources, the two characteristics are the slope of the surface brightness profile and the overall size of the cascade source. For the case of IGMF measurement from the time delayed emission, these two characteristics are the initial slope of the cascade emission light curve and the overall duration of the cascade signal. Results. We show that measurement of the slope of the cascade induced extended emission and/or light curve can both potentially provide measure of the IGMF correlation length, provided it lies within the range 10 kpc ≲ λB ≲ 1 Mpc. For correlation lengths outside this range, gamma-ray observations can provide an upper or lower bound on λB. The latter of the two methods holds great promise in the near future for providing a measurement/constraint using measurements from present/next-generation γ-ray-telescopes. Conclusions. Measurement of the IGMF correlation length will provide an important constraint on its origin. In particular, it will enable to distinguish between an IGMF of galactic wind origin from an IGMF of cosmological origin.
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•Ru nanoparticles coated by anthraquinone-2,6-disulfonate (SQ) have been prepared.•This catalyst selectively oxidizes different types of alcohols to aldehydes.•Strong interaction ...between Ru and SQ species changing electronic states was shown.•Mechanism involves abstraction by quinone of H with transfer to Ru core to form water.
Selective aerobic oxidation of alcohols to corresponding carbonyl compounds is one of the most important challenges in the modern chemical industry. The existing metal based heterogeneous catalysts provide low selectivity due to over-oxidation of aldehydes to acids and esters. We have found that coating of Ru nanoparticles by disodium anthraquinone-2,6-disulfonate (SQ) results in selective oxidation of aliphatic, unsaturated and aromatic alcohols to aldehydes. Analysis of core-shell Ru@SQ catalyst shows strong interaction between Ru and SQ leading to change of their electronic state and structure. In-situ study of alcohol oxidation using FTIR and electrochemistry indicates on hydrogen abstraction by shell quinone species with hydrogen transfer by quinone to Ru core for water generation. Thus, the catalyst behavior mimics nano-electrocell by separation of oxidation reaction over quinone and reduction of oxygen over Ru providing higher selectivity to aldehyde.
Lanthanum-containing materials are widely used in oxidative catalytic and electrocatalytic reactions such as oxidative coupling of methane (OCM) and solid oxide fuel cells (SOFCs). However, many of ...these materials are highly susceptible to air contamination which means
ex situ
characterization results generally cannot be associated with their reactivity. In this study, the activation processes of an
in situ
–prepared bulk La
2
O
2
CO
3
sample and an
ex situ
as-prepared La(OH)
3
sample are
in situ
investigated by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and online mass spectroscopy (MS). Results indicate that the La
2
O
2
CO
3
sample, during linear heating to 800°C, always contains some carbonates near the surface region, which supports a two-step model of bulk carbonate decomposition through surface sites. The La(OH)
3
sample structure evolution is more complex due to contaminations from air exposure. Together with TGA results, online mass analysis of water and CO
2
signal loss showed that three major catalyst structure phase change steps and a preheating up to 800°C are required for the as-prepared material to be transferred to La
2
O
3
. This process is carefully investigated combining the three
in situ
methodologies. XPS and XRD data further reveal transformations of variety of
in situ
surface structures and forms including hybrid phases with hydroxyl, carbonates, and oxide as the sample heated to different temperatures within the range from 200 to 800°C. The results provide useful insights on the activation and deactivation of La-contained materials.
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