ExxonMobil

About: ExxonMobil is a company organization based out in Irving, Texas, United States. It is known for research contribution in the topics: Catalysis & Polymerization. The organization has 16969 authors who have published 23758 publications receiving 535713 citations. The organization is also known as: Exxon Mobil Corporation & Exxon Mobil Corp..

Free iron clusters react readily with O2 and H2S but are inert toward methane

Abstract: Donnees de resultats representant les reactivites reelles a basse temperature des agregats de fer libre, avec addition moleculaire d'O 2 (par exemple, Fe x O 2 pour 2≤x≤15) et formation de sulfures deshydrogenes (Fe x S) en tant que processus chimique primaire. Dans le cas du metane, on n'observe pas de reactions

Chapter 2 The Optical Absorption Edge of a-Si: H

Abstract: Publisher Summary This chapter explores the effect of temperature, isochronal annealing, and preparation conditions on the optical absorption edge of a-Si:H x films The chapter describes the Tauc, Abe, and Toyazawa models The Tauc model defines the absorption edge of an amorphous semiconductor through the concept of a nondirect optical transition in which electron momentum is not conserved (total disorder) By utilizing the random phase approximation and parabolic bands, Tauc defined an optical gap E G that is widely used by experimentalists to define the position and the shape of the high-energy side of the absorption edge for a-Si:H x and other amorphous semiconductors The quantity E G is not a significant feature of the absorption edge but can be successfully correlated with the magnitude of the mobility gap deduced from transport measurements Abe and Toyazawa generalized the Tauc model to include a variable degree of Gaussian site disorder on the basis of the coherent potential approximation From this generalization, the Tauc optical gap E G becomes an additive function of structural and thermal disorder, in agreement with experiment

Effects of microporosity on sonic velocity in carbonate rocks

Abstract: The elastic moduli of a rock are affected by three main factors: pore fluid, rock framework, and pore space. In carbonate rocks, the latter two factors are a function of the depositional environment and the diagenetic history. Cementation, recrystallization, and dissolution processes can change the mineralogy and texture of the original framework and thereby alter the original grain-to-grain contacts and/or occlude pore space. Dissolution processes can enlarge interparticle pore space or dissolve grains entirely, thereby increasing porosity. These diagenetic alterations and associated changes in the rock frame and pore structure result in a wide velocity range at a given porosity.

A database of fish biotransformation rates for organic chemicals.

Abstract: Biotransformation is a key process that can mitigate the bioaccumulation potential of organic substances and is an important parameter for exposure assessments. A recently published method for estimating whole-body in vivo metabolic biotransformation rate constants (kM) is applied to a database of measured laboratory bioconcentration factors and total elimination rate constants for fish. The method uses a kinetic mass balance model to estimate rates of chemical uptake and elimination when measured values are not reported. More than 5400 measurements for more than 1000 organic chemicals were critically reviewed to compile a database of 1535 kM estimates for 702 organic chemicals. Biotransformation rates range over six orders of magnitude across a diverse domain of chemical classes and structures. Screening-level uncertainty analyses provide guidance for the selection and interpretation of kM values. In general, variation in kM estimates from different routes of exposure (water vs diet) and between fish species is approximately equal to the calculation uncertainty in kM values. Examples are presented of structure-biotransformation relationships. Biotransformation rate estimates in the database are compared with estimates of biodegradation rates from existing quantitative structure-activity relationship models. Modest correlations are found, suggesting some consistency in biotransformation capabilities between fish and microorganisms. Additional analyses to further explore possible quantitative structure-biotransformation relationships for estimating kM from chemical structure are encouraged, and recommendations for improving the database are provided.