Enteric virus infection risk from intrusion of sewage into a drinking water distribution network.

Contaminants from the soil surrounding drinking water distribution systems are thought to not enter the drinking water when sufficient internal pressure is maintained. Pressure transients may cause short intervals of negative pressure, and the soil near drinking water pipes often contains fecal material due to the proximity of sewage lines, so that a pressure event may cause intrusion of pathogens. This paper presents a risk model for predicting intrusion and dilution of viruses and their transport to consumers. Random entry and dilution of virus was simulated by embedding the hydraulic model into a Monte Carlo simulation. Special attention was given to adjusting for the coincidence of virus presence and use of tap water, as independently occurring short-term events within the longer interval that the virus is predicted to travel in any branch of the distribution system. The probability that a consumer drinks water contaminated with virus is small, but when this happens the virus concentration tends to be high and the risk of infection may be considerable. The spatial distribution of infection risk is highly heterogeneous. The presence of a chlorine residual reduces the infection risk.

Cryopreservation of hematopoietic and non-hematopoietic stem cells.

Recent studies illustrate the potential for improving the cryopreservation of stem cells. Reduced DMSO concentrations in the cryopreservation medium, post thaw washing of cells and increased cell concentration have been actively studied. Standardization of cell processing has led to the study of liquid storage prior to cryopreservation, validation of mechanical (uncontrolled rate freezing) freezing, and cryopreservation bag failure. Finally, the need for the systematic study and optimization of preservation processes has not been fulfilled. As the sources and applications of stem cells (hematopoietic and non-hematopoietic) continue to be developed, the need for effective preservation methods will only grow.

A rose by any other name is not the same: the role of orthographic knowledge in homophone confusion errors.

Homophone confusion errors were examined in a series of 6 experiments. Across a variety of tasks, readers consistently made more errors on homophone trials than on control trials. These effects were established in Experiment 1 using a semantic-decision task in which participants judged whether pairs of words were related or unrelated. For both related and unrelated trials, error rates were higher for homophones as compared with controls. Results such as these have previously been taken as evidence for the role of phonology in lexical access and reading. However, differences in orthographic knowledge (more specifically, knowledge of spelling-to-meaning correspondences) across participants and homophone items significantly predicted homophone errors across all tasks. In addition, spelling tasks and multiple-choice questionnaires revealed differences in orthographic knowledge across participants and homophone items. Although these results do not rule out a role for phonology in lexical access, they indicate that homophone confusion errors may also be due to factors other than phonology.

Numerical characterization of diffusion-based extraction in cell-laden flow through a microfluidic channel.

Cells are routinely cryopreserved in dimethyl sulfoxide (DMSO), a cryoprotective agent, for medical applications. Infusion of a DMSO-laden cell suspension results in adverse patient reactions, but current DMSO extraction processes result in significant cell losses. A diffusion-based numerical model was employed to characterize DMSO extraction in fully developed channel flow containing a wash stream flowing parallel to a DMSO-laden cell suspension. DMSO was allowed to diffuse across cell membranes as well as across the channel depth. A variety of cases were considered with the ultimate goal of characterizing the optimal geometry and flow conditions to process clinical volumes of cell suspension in a reasonable time (2-3 ml/min). The results were dependent on four dimensionless parameters: depth fraction of the DMSO-laden stream, Peclet number, cell volume fraction in the DMSO-laden stream, and cell membrane permeability parameter. Smaller depth fractions led to faster DMSO extraction but channel widths that were not practical. Higher Peclet numbers led to longer channels but smaller widths. For the Peclet values and channel depths considered (>or=500 microm) and appropriate permeability values, diffusion across cell membranes was significantly faster than diffusion across the channel depth. Cell volume fraction influenced the cross-stream diffusion of DMSO by limiting the fluid volume fraction available in the contaminant stream but did not play a significant role in channel geometry or operating requirements. The model was validated against preliminary experiments in which DMSO was extracted from suspensions of B-lymphoblast cells. The model results suggest that a channel device with practical dimensions can remove a sufficient level of contaminant within a mesoscale volume of cells in the required time.