Dynamic mathematical model of the crystallization kinetics of fats

A new model able to describe the kinetics of isothermal crystallization is presented: it is a model written in the form of a differential equation allowing use under dynamic temperature variations. It describes the crystallization process as if it is a reversible reaction with a first order forward reaction and a reverse reaction of order n. The model has the advantage of having an analytical solution under isothermal conditions that facilitates parameter estimation. The quality of this model was compared with the more traditional Avrami (with and without induction time) and Gompertz models using different model selection criteria. To show the universality of the model, different fat samples, different crystallization temperatures and different measuring techniques were used for model evaluation. The new model was selected as the best for the majority of the samples and this independent of the model selection criterion used.     

Land use regression model for ultrafine particles in Amsterdam

There are currently no epidemiological studies on health effects of long-term exposure to ultrafine particles (UFP), largely because data on spatial exposure contrasts for UFP is lacking. The objective of this study was to develop a land use regression (LUR) model for UFP in the city of Amsterdam. Total particle number concentrations (PNC), PM10, PM2.5, and its soot content were measured directly outside 50 homes spread over the city of Amsterdam. Each home was measured during one week. Continuous measurements at a central urban background site were used to adjust the average concentration for temporal variation. Predictor variables (traffic, address density, land use) were obtained using geographic information systems. A model including the product of traffic intensity and the inverse distance to the nearest road squared, address density, and location near the port explained 67% of the variability in measured PNC. LUR models for PM2.5, soot, and coarse particles (PM10, PM2.5) explained 57%, 76%, and 37% of the variability in measured concentrations. Predictions from the PNC model correlated highly with predictions from LUR models for PM2.5, soot, and coarse particles. A LUR model for PNC has been developed, with similar validity as previous models for more commonly measured pollutants.     

Time trends of selected persistent organic pollutants in lake sediments from Greenland

Sediments from seven lakes in West Greenland were used as natural archives to study past and present levels of PCBs (polychlorinated biphenyls, tri- to decachlorinated), tetra-BDE #47 (2,2',4,4'-bromodiphenyl ether), chlordane (cis- and trans-octachlordane) and HxCBz (hexachlorobenzene). The concentrations found are lower than or comparable to concentrations found in sediments from other Arctic regions and one to 2 orders of magnitude lower than concentrations typically found in sediments at lower latitudes. The observed temporal trends (direct and indirect dating) show a decreasing total PCB concentration. Even though local contamination sources exist, the POP deposition in the studied area is most likely a result from long-range transport. The hypothesis about "cold condensation" suggests a latitudinal fractionation to occur between different volatile compounds during the transport toward the pole. In this study a time delay in the deposition for the low-chlorinated PCBs (tri- and tetrachlorinated), compared to their emission histories and compared to higher chlorinated PCBs, was indicated. Although very low tetra-BDE #47 concentrations are observed in this study, there are indications for an increasing concentration in recent sediment layers that may reflect increasing environmental concentrations at lower latitudes. The investigated pesticides are still in use at lower latitudes, however neither chlordane nor HxCBz show any distinct temporal trend of increasing or decreasing concentration toward the sediment surface.     

The stability of individual response styles.

Modeling capabilities for longitudinal data have progressed considerably, but questions remain on the extent to which method bias may negatively affect the validity of longitudinal survey data. The current study addresses the stability of individual response styles. We set up a longitudinal data collection in which the same respondents filled out 2 online questionnaires with nonoverlapping sets of heterogeneous items. Between data collections, there was a 1-year time gap. We simultaneously modeled 4 response styles that capture the major directional biases in questionnaire responses: acquiescence, disacquiescence, midpoint, and extreme response style. Drawing from latent state–trait theory, we specified a 2nd-order factor model with time-invariant and time-specific response style factors and a specifically designed covariance structure for the residual terms. The results indicate that response styles have an important stable component, a small part of which can be explained by demographics. The meaning and implications of these findings are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Global learning on carbon capture and storage: A call for strong international cooperation on CCS demonstration

Closing the gap between carbon dioxide capture and storage (CCS) rhetoric and technical progress is critically important to global climate mitigation efforts. Developing strong international cooperation on CCS demonstration with global coordination, transparency, cost-sharing and communication as guiding principles would facilitate efficient and cost-effective collaborative global learning on CCS, would allow for improved understanding of the global capacity and applicability of CCS, and would strengthen global trust, awareness and public confidence in the technology.