Characterization of polylactic acid films for food packaging as affected by dielectric barrier discharge atmospheric plasma

Dielectric barrier discharge (DBD) air plasma is a novel technique for in-package decontamination of food, but it has not been yet applied to the packaging material. Characterization of commercial polylactic acid (PLA) films was done after in-package DBD plasma treatment at different voltages and treatment times to evaluate its suitability as food packaging material. DBD plasma increased the roughness of PLA film mainly at the site in contact with high voltage electrode at both the voltage levels of 70 and 80 kV. DBD plasma treatments did not induce any change in the glass transition temperature, but significant increase in the initial degradation temperature and maximum degradation temperature was observed. DBD plasma treatment did not adversely affect the oxygen and water vapor permeability of PLA. A very limited overall migration was observed in different food simulants and was much below the regulatory limits. Industrial relevance: In-package DBD plasma is a novel and innovative approach for the decontamination of foods with potential industrial application. This paper assesses the suitability of PLA as food packaging material for cold plasma treatment. It characterizes the effect of DBD plasma on the packaging material when used for in-package decontamination of food. The work described in this research offers a promising alternative to classical methods used in fruit and vegetable industries where in-package DBD plasma can serve as an effective decontamination process and avoids any post-process recontamination or hazards from the package itself.

On the nature of candidate luminous blue variables in M 33

Context. Luminous blue variables (LBVs) are a class of highly unstable stars that have been proposed to play a critical role in massive stellar evolution as well as being the progenitors of some of the most luminous supernovae known. However the physical processes underlying their characteristic instabilities are currently unknown. Aims. In order to provide observational constraints on this behaviour we have initiated a pilot study of the population of (candidate) LBVs in the Local Group galaxy M 33. Methods. To accomplish this we have obtained new spectra of 18 examples within M 33. These provide a baseline of ≥ 4 yr with respect to previous observations, which is well suited to identifying LBV outbursts. We also employed existing multi-epoch optical and mid-IR surveys of M 33 to further constrain the variability of the sample and search for the presence of dusty ejecta. Results. Combining the datasets reveals that spectroscopic and photometric variability appears common, although in the majority of cases further observations will be needed to distinguish between an origin for this behavour in short lived stochastic wind structure and low level photospheric pulsations or coherent long term LBV excursions. Of the known LBVs we report a hitherto unidentified excursion of M 33 Var C between 2001-5, while the transition of the WNLh star B517 to a cooler B supergiant phase between 1993−2010 implies an LBV classification. Proof-of-concept quantitative model atmosphere analysis is provided for Romano’s star; the resultant stellar parameters being consistent with the finding that the LBV excursions of this star are accompanied by changes in bolometric luminosity. The combination of temperature and luminosity of two stars, the BHG [HS80] 110A and the cool hypergiant B324, appear to be in violation of the empirical Humphreys-Davidson limit. Mid-IR observations demonstrate that a number of candidates appear associated with hot circumstellar dust, although no objects as extreme as η Car are identified. The combined dataset suggests that the criteria employed to identify candidate LBVs results in a heterogeneous sample, also containing stars demonstrating the B[e] phenomenon. Of these, a subset of optically faint, low luminosity stars associated with hot dust are of particular interest since they appear similar to the likely progenitor of SN 2008S and the 2008 NGC 300 transient (albeit suffering less intrinsic extinction). Conclusions. The results of such a multiwavelength observational approach, employing multiplexing spectrographs and supplemented with quantitative model atmosphere analysis, appears to show considerable promise in both identifying and characterising the physical properties of LBVs as well as other short lived phases of massive stellar evolution.

El Estribo Volcanic Complex: Evolution from a shield volcano to a cinder cone, Pátzcuaro Lake, Michoacán, México

El Estribo Volcanic Complex (EVC) is located in the northern part of the Michoacán–Guanajuato Volcanic Field within the Trans-Mexican Volcanic Belt (TMVB). El Estribo is located at the southern edge of the E-W Pátzcuaro fault that belongs to the Pátzcuaro-Jarácuaro graben, a western extension of the E-W Morelia–Acambay fault system. Stratigraphy, geochronology, chemistry, and mineral assemblages suggest that the volcanic complex was constructed in two periods separated by a ~ 100 ka volcanic hiatus: a) emission of lava flows that constructed a shield volcano between 126 ka, and b) mixed phreatomagmatic to Strombolian activity that formed a cinder cone ~ 28 ka. The magmas that fed these monogenetic volcanoes were able to use the same feeding system. The cinder cone itself was constructed by Strombolian fallouts and remobilized scoria beds, followed by an erosion period, and by a mixed phreatomagmatic to magmatic phase (Strombolian fallouts ending with lava flows). Soft-sedimentary deformation of beds and impact sags, cross-bedding, as well as pitting and hydrothermal cracks found in particles support the phreatomagmatic phase. The erupted magmas through time ejected basaltic andesitic lava flows (56.21–58.88% SiO2) that built the shield volcano and then basaltic andesitic scoria (57.65–59.05% SiO2) that constructed the cinder cone. Although they used the same feeding system, the geochemical data and the mineral chemistry of the magmas indicate that the shield volcano and the cinder cone were fed by different magma batches erupted thousands of years apart. Therefore, the location of El Estribo Volcanic Complex along an E-W fault that has generated two sector collapses of the shield volcano to the north may be directly linked to this complex redistribution of the magmatic paths to the surface. Our findings show that magmatic feeding systems within monogenetic volcanic fields could be long lived, questioning the classic view of the monogenetic nature of their volcanoes and yielding information about the potential volcanic risk of these settings, usually considered risk-free.

Effect of the porous structure in carbon materials for CO2 capture at atmospheric and high-pressure

Activated carbons prepared from petroleum pitch and using KOH as activating agent exhibit an excellent behavior in CO2 capture both at atmospheric (∼168 mg CO2/g at 298 K) and high pressure (∼1500 mg CO2/g at 298 K and 4.5 MPa). However, an exhaustive evaluation of the adsorption process shows that the optimum carbon structure, in terms of adsorption capacity, depends on the final application. Whereas narrow micropores (pores below 0.6 nm) govern the sorption behavior at 0.1 MPa, large micropores/small mesopores (pores below 2.0–3.0 nm) govern the sorption behavior at high pressure (4.5 MPa). Consequently, an optimum sorbent exhibiting a high working capacity for high pressure applications, e.g., pressure-swing adsorption units, will require a poorly-developed narrow microporous structure together with a highly-developed wide microporous and small mesoporous network. The appropriate design of the preparation conditions gives rise to carbon materials with an extremely high delivery capacity ∼1388 mg CO2/g between 4.5 MPa and 0.1 MPa. Consequently, this study provides guidelines for the design of carbon materials with an improved ability to remove carbon dioxide from the environment at atmospheric and high pressure.