Pushmepullyou: An efficient micro-swimmer

The swimming of a pair of spherical bladders that change their volumes and mutual distance is efficient at low Reynolds numbers and is superior to other models of artificial swimmers. The change of shape resembles the wriggling motion known as {\it metaboly} of certain protozoa.Comment: Minor rephrasing and changes in style; short explanations adde

Exposure factors manual

ABSTRACT: Assessing health risks associated with potential exposure to chemicals from petroleum or petrochemical operations requires the consideration of multiple exposure pathways. These pathways include ingestion of water, food, or soil, inhalation of vapors or airborne particulate, and dermal absorption from contaminated soil, water, or by direct skin contact. To estimate the exposures for each pathway, a number of variables related to exposure, that is, exposure factors, are needed. Some categories of exposure factors include physiologic factors (e.g., body weight), time-activity factors (e.g., time spent at home), and contact rate factors (e.g., soil ingestion rate). This manual is organized by exposure factor category and includes a description of selected exposure factors commonly used in risk assessments, a brief summary, and an evaluation of the current scientific data supporting a recommended point value for each factor, and available information on the known distributions. It is hoped that this information will promote consistency and quality among various risk assessment activities

Kinetic analysis of the partial synthesis of artemisinin: Photooxygenation to the intermediate hydroperoxide

The price of the currently best available antimalarial treatment is driven in large part by the limited availability of its base drug compound artemisinin. One approach to reduce the artemisinin cost is to efficiently integrate the partial synthesis of artemisinin starting from its biological precursor dihydroartemisinic acid (DHAA) into the production process. The optimal design of such an integrated process is a complex task that is easier to solve through simulations studies and process modelling. In this article, we present a quantitative kinetic model for the photooxygenation of DHAA to an hydroperoxide, the essential initial step of the partial synthesis to artemisinin. The photooxygenation reactions were studied in a two-phase photo-flow reactor utilizing Taylor flow for enhanced mixing and fast gas-liquid mass transfer. A good agreement of the model and the experimental data was achieved for all combinations of photosensitizer concentration, photon flux, fluid velocity and both liquid and gas phase compositions. Deviations between simulated predictions and measurements for the amount of hydroperoxide formed are 7.1 % on average. Consequently, the identified and parameterized kinetic model is exploited to investigate different behaviors of the reactor under study. In a final step, the kinetic model is utilized to suggest attractive operating windows for future applications of the photooxygenation of DHAA exploiting reaction rates that are not affected by mass transfer limitations