The Yen−Mullins model, also known as the modified Yen model, specifies the predominant molecular and colloidal structure of asphaltenes in crude oils and laboratory solvents and consists of the following: The most probable asphaltene molecular weight is ∼750 g/mol, with the island molecular architecture dominant. At sufficient concentration, asphaltene molecules form nanoaggregates with an aggregation number less than 10. At higher concentrations, nanoaggregates form clusters again with small aggregation numbers. The Yen−Mullins model is consistent with numerous molecular and colloidal studies employing a broad array of methodologies. Moreover, the Yen−Mullins model provides a foundation for the development of the first asphaltene equation of state for predicting asphaltene gradients in oil reservoirs, the Flory−Huggins− Zuo equation of state (FHZ EoS). In turn, the FHZ EoS has proven applicability in oil reservoirs containing condensates, black oils, and heavy oils. While the development of the Yen−Mullins model was founded on a very large number of studies, it nevertheless remains essential to validate consistency of this model with important new data streams in asphaltene science. In this paper, we review recent advances in asphaltene science that address all critical aspects of the Yen−Mullins model, especially molecular architecture and characteristics of asphaltene nanoaggregates and clusters. Important new studies are shown to be consistent with the Yen−Mullins model. Wide ranging studies with direct interrogation of the Yen−Mullins model include detailed molecular decomposition analyses, optical measurements coupled with molecular orbital calculations, nuclear magnetic resonance (NMR) spectroscopy, centrifugation, direct-current (DC) conductivity, interfacial studies, small-angle neutron scattering (SANS), and small-angle X-ray scattering (SAXS), as well as oilfield studies. In all cases, the Yen−Mullins model is proven to be at least consistent if not valid. In addition, several studies previously viewed as potentially inconsistent with the Yen−Mullins model are now largely resolved. Moreover, oilfield studies using the Yen−Mullins model in the FHZ EoS are greatly improving the understanding of many reservoir concerns, such as reservoir connectivity, heavy oil gradients, tar mat formation, and disequilibrium. The simple yet powerful advances codified in the Yen−Mullins model especially with the FHZ EoS provide a framework for future studies in asphaltene science, petroleum science, and reservoir studies.

The molecular architecture of asphaltenes is still a matter of debate. Some literature reports provide evidence that the contrast of petroleum asphaltenes versus coal-derived asphaltenes is useful for understanding the governing principles of asphaltene identity. Coal-derived asphaltenes provide an excellent test for understanding the relationship of asphaltene molecular architecture with asphaltene properties. Diffusion measurements have shown that coal-derived asphaltenes are half the size of many crude oil asphaltenes, but there are relatively few studies comparing coal-derived and petroleum asphaltenes using liquid state 13C NMR. 13C NMR confirms that the molecular sizes of these coal-derived asphaltenes are smaller than virgin petroleum asphaltenes. DEPT-45 experiments were performed in order to determine the relative amount of nonprotonated and protonated carbon in the aromatic region of the spectrum. In contrast to previous NMR work on asphaltenes that ignored interior bridgehead carbon, we show this is an important component of asphaltenes and that correctly accounting for this carbon enables proper determination of the number of fused rings. XRS data supports interpreting the NMR data with a model that weighs circularly condensed structures more heavily than linearly condensed structures. Significantly more carbon exists in chains at least 9 carbons long in petroleum asphaltenes (≥7%) compared to coal-derived asphaltenes (≥1%).

No abstract

No abstract

The spin lattice relaxation time, T , , quadrupolar coupling constant, and chemical shielding tensor elements of several for IH's. Typical relaxation times for 87Rb are in the range of 100-300 ms and 50-300 ms for 85Rb. The Q , values are in the range of 7-14 MHz for 85Rb and 3-1 1 MHz for 87Rb. A program was created to numerically simulate and fit experimental powder patterns for the &/2 central transition, where the principal axis systems (PAS) of the shielding and quadrupole tensors are not coincident. The analysis shows that having both nuclides available with significantly different quadrupole coupling constants makes the general line-shape problem more tractable. That is, the 85Rb data provides an excellent visualization of chemically different rubidium atoms when there are significant differences in the value of Q , . Such data would be difficult to extract from the corresponding 87Rb line shapes due to the smaller value of Q , . The 87Rb nuclide, however, because of its smaller value of Qa, provides an excellent opportunity to observe the consequences of the noncoincident PAS frames between the shielding and quadrupole tensors.rubidium salts have been surveyed at the frequency 130.88 MHz for 9, ' 7Rb and 38.64 MHz for 85Rb, i.e. 9.4T, or 400 MHz IntroductionRubidium has two stable isotopes, 85Rb (I = 5 / 2 ) and 87Rb (I = 3/2), which are amenable to the NMR experiment. The natural abundances of these nuclides are 72.8% and 27.2% for 85Rb and 87Rb, respectively. Typically, only the *1/2 central transition is observed in solid-state rubidium NMR. The other transitions are very broad, and the quadrupole coupling constant is sufficiently large to prevent excitation of these transitions. The moderate

SummaryThis paper represents an initial effort to explore the empirical relationship between business ideologies and perceptions of organizational downsizing. The results of four studies, two conducted in the US and one each in Singapore and Korea, suggest that respondents' belief in the ideology of employee self-reliance reduces the degree to which they perceive layoffs as a breach of the psychological contract. This finding appears to generalize to respondents' perceptions of their own layoffs and also to respondents' perceptions of layoffs happening to others. We spell out the implications of these results for the evolving theory of the ideological foundations of perceptions of downsizing.

No abstract

No abstract