Determination of Levoglucosan in Particulate Matter Reference Materials

Source identification is critical for the effective management of air pollution. The ratio of levoglucosan (1,6-anhydro- β -D-glucose) to organic carbon has been used to identify and quantify the contribution of biomass combustion to the organic carbon content in aerosols. Therefore, accurate levoglucosan measurements in particulate matter are important. This study determined levoglucosan concentrations in urban dust Standard Reference Materials (SRMs) 1649a and 1648 available from the National Institute of Standards and Technology (NIST) as well as two particulate matter samples with particle sizes nominally 2.5 μ m and smaller collected in Baltimore, MD. Levoglucosan was extracted using both pressurized fluid and Soxhlet techniques. Quantification was performed with gas chromatography/mass spectrometry (GC/MS) using a deuterated levoglucosan internal standard and two different GC columns. Levoglucosan concentrations were 81.1 μ g g^?1 with a standard deviation of 9.4 μ g g^?1 (n = 9) for SRM 1649a, 107 μ g g^?1 with a standard deviation of 18 μ g g ^?1 (n = 8) for SRM 1648, 225 μ g g^?1 (standard deviation of 41 μ g g^?1 n = 4) and 138 μ g g^?1 (standard deviation of 39 μ g g ^{? 1} n = 5) for the two fine particulate matter samples collected in Baltimore, MD.     

Effect of type of polymerization catalyst system on the degradation and stabilization of polyethylenes in the melt state—Part 4: Comparative antioxidant effectiveness on organoleptic extractables

Several polyethylene resins using Ziegler, metallocene, and Phillips catalyst technologies were examined to obtain more detailed information about the effect of different polymerization catalyst systems on the production of extractable thermo-oxidative degradation products formed during melt processing cycles. This produces volatile organoleptic components (VOCs and extractable) such as hydrocarbons, alcohols, aldehydes, ketones, and carboxylic acids. Although some of the oxidation products are in-chain bound, many are produced as free, easily extractable entities or volatile components. The purpose of this study is to identify the nature of the products by gas chromatography–mass spectrometry (GC–MS) and FTIR analysis. The identity of the VOCs formed is necessary to modify the product's quality or establish which are toxic and/or leachable with food products. The results show that the evolution of carbonyl products, nature, and quantity is influenced significantly by the polymer type and catalyst used. Over 300 organoleptics low molar mass degradation products, such as alkane, alkene, carbonyl, and alcohol functionalities were detected by GC–MS analysis coupled with FTIR analysis on hexane extractables. Certain stabilizers can control the generation of certain functionalities and inhibit others. Of importance was the discovery of the relationship between additive activity and structure and inhibition of the formation of specific types of oxidation functionalities to a particular catalyst system.     

Hybrid inorganic-organic polymer electrolytes: synthesis, FT-Raman studies and conductivity of {Zr[(CH2CH2O)8.7]ρ/(LiClO4)z}n network complexes

This paper describes the synthesis and characterization of three-dimensional hybrid inorganic-organic networks prepared by a polycondensation reaction between Zr(O(CH₂)₃CH₃)₄ and polyethylene glycol 400 (PEG400). Eleven hybrid networks doped with varying concentrations of LiClO₄ salt were prepared. On the basis of analytical data and FT-Raman studies it was concluded that these polymer electrolytes consist of inorganic-organic networks with zirconium atoms bonded together by PEG400 bridges. These polymers are transparent with a solid rubber consistency and are very stable under inert atmosphere. Scanning electron microscopy revealed a smooth glassy surface. X-ray fluorescence microanalysis with energy dispersive spectroscopy demonstrated that all the constituent elements are homogeneously distributed in the materials. Thermogravimetric measurements revealed that these materials are thermally stable up to 262 °C. Differential Scanning Calorimetry measurements indicated that the glass transition temperature T_g of these inorganic-organic hybrids varies from −43 to −15 °C with increasing LiClO₄ concentration. FT-Raman investigations revealed the TGT (T=trans, G=gauche) conformation of polyether chains and allowed characterization of the types of ion-ion and ion-polymer host interactions in the bulk materials. The conductivity of the materials at different temperatures was determined by impedance spectroscopy over the 20 Hz-1 MHz frequency range. Results indicated that the materials conduct ionically and that their ionic conductivity is strongly influenced by the segmental motion of the polymer network and the type of ionic species distributed in the bulk material. Finally, it is to be highlighted that the hybrid network with a n_Li/n_O molar ratio of 0.0223 shows a conductivity of ca. 1×10⁻⁵ S cm⁻¹ at 40 °C.     

Sonochemically Prepared high Dispersed Ru/TiO2 Mesoporous Catalyst for Partial Oxidation of Methane to Syngas

Highly dispersed Ru nanoparticles on mesoporous TiO₂ have been synthesized by a one-step ultrasound assisted polyol reduction procedure. The catalysts have been characterized by XRD, TEM and HR-TEM, EDX, BET and TPR methods. It has been demonstrated that the sonochemical method reduces the Ru⁺³ ions creating a narrow size distribution of metallic nanoparticles deposited on the mesoporous support without damaging its pore structure. The nanoparticles of Ru are highly dispersed and stable because of their incorporation into the mesopores, and the strong metal-support interaction. The catalytic properties of Ru/TiO₂(MSP) have been tested in the partial oxidation of methane, and high activity and selectivity towards CO and H₂ have been demonstrated.     

Pore evolution and compaction behaviour of spray-dried bodies for porcelain stoneware slabs

The compaction behavior of spray-dried powders has turned into concern in porcelain stoneware manufacturing due to the increasing diffusion of large slabs. It is necessary to fill a knowledge gap between the compaction behavior with conventional presses and novel technologies. For this purpose, eighteen industrially-manufactured spray dried bodies were characterized for specific properties connected to the compaction behavior (curves of bulk density, intergranular and intragranular porosity in function of applied load, apparent yield strength). In addition, the firing behavior was investigated in order to reveal any effect of dry bulk density on firing shrinkage and bulk density of fired samples. Powder compressibility is within 50% and 55% (Carr index) and is primarily controlled by moisture. Two regimes are found: low pressure (fast density increasing by granule cave in and closure of intergranular porosity) and high pressure (slow density gain by downsizing microporosity). A peculiar mechanism is unveiled: granules squeeze in the low-P regime and further densification is achieved through microfracture around individual agglomerate. A phenomenological model is illustrated for the compaction of spray-dried powders. In conclusion, the performance of spray dried bodies during compaction is crucial to control the uniformity, in terms of porosity and bulk density, which has important repercussions on the properties of final slabs, especially differential shrinkages and deformation during firing due to density gradients.     

Time‐series models with an EGB2 conditional distribution

A time‐series model in which the signal is buried in noise that is non‐Gaussian may throw up observations that, when judged by the Gaussian yardstick, are outliers. We describe an observation‐driven model, based on an exponential generalized beta distribution of the second kind (EGB2), in which the signal is a linear function of past values of the score of the conditional distribution. This specification produces a model that is not only easy to implement but which also facilitates the development of a comprehensive and relatively straightforward theory for the asymptotic distribution of the maximum‐likelihood (ML) estimator. Score‐driven models of this kind can also be based on conditional t distributions, but whereas these models carry out what, in the robustness literature, is called a soft form of trimming, the EGB2 distribution leads to a soft form of Winsorizing. An exponential general autoregressive conditional heteroscedastic (EGARCH) model based on the EGB2 distribution is also developed. This model complements the score‐driven EGARCH model with a conditional t distribution. Finally, dynamic location and scale models are combined and applied to data on the UK rate of inflation.     

Interactions of Cr(VI) and Cr(III) with isolated rat liver mitochondria

The mechanism of interaction of Cr(VI) with isolated rat liver mitochondria was investigated in this study. The results suggest that Cr(VI) induces the opening of the membrane permeability transition pore (MPT). The phenomenon is cyclosporine-sensitive and is in agreement with the cyclosporine-sensitive apoptosis observed in the cells incubated with this compound. Moreover the action of Cr(III), that is formed in the cells by a reduction of Cr(VI), has been also analysed. The results obtained demonstrated that the Cr(III) does not induce the opening of the MPT in isolated mitochondria, but it has a protective effect in preventing Cr(VI) MPT opening. Therefore, these results suggest that apoptosis is regulated by a balance between Cr(VI) accumulation in the cytoplasm and Cr(III) formation.