Kinematic study of planetary nebulae in NGC 6822

By measuring precise radial velocities of planetary nebulae (which belong to the intermediate age population), H II regions, and A-type supergiant stars (which are members of the young population) in NGC 6822, we aim to determine if both types of population share the kinematics of the disk of H I found in this galaxy. Spectroscopic data for four planetary nebulae were obtained with the high spectral resolution spectrograph Magellan Inamori Kyocera Echelle (MIKE) on the Magellan telescope at Las Campanas Observatory. Data for other three PNe and one H II region were obtained from the SPM Catalog of Extragalactic Planetary Nebulae which employed the Manchester Echelle Spectrometer attached to the 2.1m telescope at the Observatorio Astron\'omico Nacional, M\'exico. In the wavelength calibrated spectra, the heliocentric radial velocities were measured with a precision better than 5-6 km s$^{-1}$. Data for three additional H II regions and a couple of A-type supergiant stars were collected from the literature. The heliocentric radial velocities of the different objects were compared to the velocities of the H i disk at the same position. From the analysis of radial velocities it is found that H II regions and A-type supergiants do share the kinematics of the H I disk at the same position, as expected for these young objects. On the contrary, planetary nebula velocities differ significantly from that of the H I at the same position. The kinematics of planetary nebulae is independent from the young population kinematics and it is closer to the behavior shown by carbon stars, which are intermediate-age members of the stellar spheroid existing in this galaxy. Our results are confirming that there are at least two very different kinematical systems in NGC 6822

Effect of biodiesel-derived impurities (acetic acid, methanol and potassium hydroxide) on the aqueous phase reforming of glycerol

This work analyses the influence of three biodiesel-derived impurities (CH3OH, CH3COOH and KOH) on the aqueous phase reforming of glycerol at 220 °C and 44 bar using a Ni-La/Al2O3 catalyst. The experiments were planed according to a factorial 2k design and analysed by means of an analysis of variance (ANOVA) test to identify the effect of each impurity and all possible binary and ternary combinations. The presence of CH3OH decreased the glycerol conversion, while CH3COOH and KOH decreased and increased the gas production, respectively. Catalyst deactivation took place under acidic conditions due to the loss of part of the active phase of the catalyst through leaching. The gas phase was made up of H2, CO2, CO and CH4. KOH exerted the greatest influence on the gas composition, increasing H2 production due to the greater gas production and the lower H2 consumption in the hydrogenation reactions. The liquid phase was made up of aldehydes, monohydric and polyhydric alcohols, C3 and C4 ketones and esters. CH3OH increased the proportion of monohydric alcohols, while CH3COOH promoted dehydration reactions, leading to an increase in the relative amount of C3-ketones

An insight into the separation of 1, 2-propanediol, ethylene glycol, acetol and glycerol from an aqueous solution by adsorption on activated carbon

Glycerol conversion processes such as aqueous phase reforming and hydrogenolysis generate value-added compounds highly diluted in water. Because distillation is a high energy demand separation step, adsorption could be an attractive alternative to recover these chemicals. Adsorption isotherms of 1, 2-propanediol, acetol, ethylene glycol and glycerol onto activated carbon were determined by batch adsorption experiments. These isotherms were fitted slightly better to the Freundlich equation than to the Langmuir equation. Acetol is the compound with the highest adsorption at concentrations smaller than 1 M. Properties of the adsorbate such as the -OH group number, chain length, molecular size and dipole moment, besides characteristics of the adsorbent such as the surface area, oxygen and ash content, are considered to explain the observed results. Moreover, adsorption experiments were performed with mixtures of compounds and it was determined that the molar amount adsorbed is less than predicted from the adsorption isotherms of the individual compounds treated separately. In addition, the influence of the activated carbon thermal pretreatment temperature on the adsorption capacity has been studied, the optimum being 800¿C. An analysis of the influence of the activated carbon characteristics showed that the most important parameters are the total pore volume and the ash content. © 2021 by the authors. Licensee MDPI, Basel, Switzerland

Cheese whey valorisation: Production of valuable gaseous and liquid chemicals from lactose by aqueous phase reforming

Cheese effluent management has become an important issue owing to its high biochemical oxygen demand and chemical oxygen demand values. Given this scenario, this work addresses the valorisation of lactose (the largest organic constituent of this waste) by aqueous phase reforming, analysing the influence of the most important operating variables (temperature, pressure, lactose concentration and mass of catalyst/lactose mass flow rate ratio) as well as optimising the process for the production of either gaseous or liquid value-added chemicals. The carbon converted into gas, liquid and solid products varied as follows: 5–41%, 33–97% and 0–59%, respectively. The gas phase was made up of a mixture of H2 (8–58 vol.%), CO2 (33–85 vol.%), CO (0–15 vol.%) and CH4 (0–14 vol.%). The liquid phase consisted of a mixture of aldehydes: 0–11%, carboxylic acids: 0–22%, monohydric alcohols: 0–23%, polyhydric-alcohols: 0–48%, C3-ketones: 4–100%, C4-ketones: 0–18%, cyclic-ketones: 0–15% and furans: 0–85%. H2 production is favoured at high pressure, elevated temperature, employing a high amount of catalyst and a concentrated lactose solution. Liquid production is preferential using diluted lactose solutions. At high pressure, the production of C3-ketones is preferential using a high temperature and a low amount of catalyst, while a medium temperature and a high amount of catalyst favours the production of furans. The production of alcohols is preferential using medium temperature and pressure and a low amount of catalyst

Scaling and universality of critical fluctuations in granular gases

The global energy fluctuations of a low density gas granular gas in the homogeneous cooling state near its clustering instability are studied by means of molecular dynamics simulations. The relative dispersion of the fluctuations is shown to exhibit a power-law divergent behavior. Moreover, the probability distribution of the fluctuations presents data collapse as the system approaches the instability, for different values of the inelasticity. The function describing the collapse turns out to be the same as the one found in several molecular equilibrium and non-equilibrium systems, except for the change in the sign of the fluctuations

Influence of the Yesa reservoir on floods of the Aragón River, central Spanish Pyrenees

International audienceThe Yesa reservoir, the largest Pyrenean reservoir, was constructed in 1959 to supply water to new irrigated areas in the Ebro Depression, NE Spain. It is filled from October to May-June and then releases large quantities of water in the summer via the Bardenas Canal. The results confirm that the frequency of floods downstream of the dam decreased. The reduction mainly depends on two factors: i) the water storage level, and ii) the season of the year. Floods are very well controlled when the reservoir level is lower than 50%. Between 50 and 70%, only the highest floods are controlled. Finally, the reservoir retains mainly autumn and spring floods; most winter floods are released downstream to ensure the safety of the dam. Keywords: reservoir, flood control, flood seasonality, flood frequency, river regime, Pyrenees</p

Study of ni/al-fe catalyst stability in the aqueous phase hydrogenolysis of glycerol

The present work studied the stability and reusability of Ni/Al-Fe catalyst in the aqueous phase hydrogenolysis of glycerol without external hydrogen addition. The catalyst based on 28 molar % of Ni with 3/1 molar ratio of Al/Fe was prepared through co-precipitation. This catalyst presented the best performance in our last study which compares several Ni/Al-Fe catalysts with different molar ratios of Al/Fe. To see the influence of the pressurized water on the physicochemical characteristics of Ni/Al-Fe catalyst, a test of up to 9 h has been carried out. Fresh and used catalysts were characterized by various techniques: X-ray Diffraction (XRD), N2-physisorption, field emission scanning electron microscopy (FESEM) and STEM. Glycerol conversion and carbon yield to gases and liquids did not vary significantly when compared at 3 h and 9 h. Furthermore, the morphology of the catalyst remains stable after continuous recycling under severe hydrothermal conditions. The nickel rich phase of the catalyst, which was determined by XRD and scanning transmission electron microscopy (STEM) techniques, showed a stable size after 9 h under reaction

Statistical tests of symbolic dynamics

A novel general method for constructing nonparametric hypotheses tests based on the field of symbolic analysis is introduced in this paper. Several existing tests based on symbolic entropy that have been used for testing central hypotheses in several branches of science (particularly in economics and statistics) are particular cases of this general approach. This family of symbolic tests uses few assumptions, which increases the general applicability of any symbolic-based test. Additionally, as a theoretical application of this method, we construct and put forward four new statistics to test for the null hypothesis of spatiotemporal independence. There are very few tests in the specialized literature in this regard. The new tests were evaluated with the mean of several Monte Carlo experiments. The results highlight the outstanding performance of the proposed test. © 2021 by the authors. Licensee MDPI, Basel, Switzerland