34 research outputs found
Bayesian treatment of a chemical mass balance receptor model with multiplicative error structure
The chemical mass balance (CMB) receptor model is commonly used in source apportionment studies as a means for attributing measured airborne particulate matter (PM) to its constituent emission sources. Traditionally, error terms (e.g., measurement and source profile uncertainty) associated with the model have been treated in an additive sense. In this work, however, arguments are made for the assumption of multiplicative errors, and the effects of this assumption are realized in a Bayesian probabilistic formulation which incorporates a 'modified' receptor model. One practical, beneficial effect of the multiplicative error assumption is that it automatically precludes the possibility of negative source contributions, without requiring additional constraints on the problem. The present Bayesian treatment further differs from traditional approaches in that the source profiles are inferred alongside the source contributions. Existing knowledge regarding the source profiles is incorporated as prior information to be updated through the Bayesian inferential scheme. Hundreds of parameters are therefore present in the expression for the joint probability of the source contributions and profiles (the posterior probability density function, or PDF), whose domain is explored efficiently using the Hamiltonian Markov chain Monte Carlo method. The overall methodology is evaluated and results compared to the US Environmental Protection Agency's standard CMB model using a test case based on PM data from Fresno, California. (c) 2008 Elsevier Ltd. All rights reserved
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The N=90 transitional nuclei {sup 150}Nd and {sup 152}Sm revisited
The purpose of this paper is to show that recent data on the ground-state band and excited states based on the 0{sub 2}{sup +} level in {sup 15}Nd and {sup 152}Sm, especially the measured B(E2) values, can be well described by including a {Delta}K = 0 coupling between rotational bands. This is contrary to recent statements in the literature. The experimental data are compared with models which have supported the widely differing interpretations of these transitional nuclei. These interpretations include describing excited states as rotational excitations of single-phonon states, the multiphonon ''phase coexistence'' picture, and the X(5) critical-point description