Impact of simulated solar irradiation on disinfection byproduct precursors

The Sacramento-San Joaquin Delta is the major drinking water source for 23 million California residents. Consequently, many studies have examined disinfection byproduct (DBP) formation in relation to Delta dissolved organic carbon (DOC) concentration. However, DOC characteristics within the Delta are not the same as those entering downstream water treatment facilities. As water is transferred to Southern California through the California Aqueduct, a 714.5 km-open channel, it is exposed to sunlight, potentially altering DBP precursors. We collected water from three sites within the Delta and one nearthe California Aqueduct, representing different DOC sources, and irradiated them in a solar simulator at a dose equivalent to that received during four days conveyance in the aqueduct. Photolytic changes in DOC were assessed by measuring CO2 and organic acid production, fluorescence, and ultraviolet absorbance over time. Trihalomethane (THM) and haloacetic acid (HAA) formation potentials, as well as the distribution of hydrophobic, transphilic, and hydrophilic acid fractions were determined at exposures equivalent to one and four days. Solar irradiation significantly decreased ultraviolet absorbance and fluorescence intensity, produced organic acids, and increased the hydrophilic fraction of waters. These changes in DOC caused a shift in bromine incorporation among the THM and HAA species. Our results are the first to demonstrate the importance of sunlight in altering DOC with respect to DBP formation.     

Advances in Modeling Completely Mixed Flow Reactors for Ion Exchange

This work advances the mathematical modeling of ion exchange treatment in completely mixed flow reactors in which there is recycle and regeneration of the ion exchange resin. The most common application of this process is magnetic ion exchange resin to remove dissolved organic carbon from raw drinking water. The motivation for this work was the complex distribution of resin particle ages and sizes that result from the recycle and regeneration processes. The newly developed model uses a single “age-averaged” diffusion equation to represent resin particle age as compared with the previous Monte Carlo model that uses a large number of diffusion equations to represent various resin particle ages. Advantages of the age-averaged model over the Monte Carlo model include a closed-form analytical solution for the steady-state case of the model, advanced numerical techniques used for the nonsteady-state case of the model, and model simulations require much less computational time and yield more accurate results. The age-averaged model is a robust numerical tool that can be used to evaluate a range of treatment scenarios as a result of these advancements.     

A rejoinder to "Psychotherapy research ethics: Continuing the debate on controlled clinical trials."

Responds to C. A. Heflinger's (1987) critique of the present authors (1986) by reiterating their concern for the principle of autonomy. The present authors note that all patients were fully informed about the research plan and their right to withdraw. Nonetheless, the ethical criticism offered by Heflinger regarding randomization cannot be entirely dismissed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Spontaneous and Light-Induced Resistive Transitions in Superconducting Thin Film Bridges

In order to study dynamically the resistive states which appear as jumps in the I–V curves of narrow bridges, we have submitted YBaCuO and Nb films to nanosecond current steps and laser pulses simultaneously. In constant current feed, the distinction between hot spots (HS) and phase-slip centers (PSCs) is unambiguous, since HS are compelled to grow or decay, at variance with the stable-in-time PSCs. Thanks to the transient method we show that, even if Joule dissipation associated to a current I is virtually sufficient to sustain the film above T_c, the zero resistance state remains metastable: a hot spot does not arise unless initiated by a PSC, which fact was not reported before. The domains of occurrence of HS and PSCs were then organized in a current–temperature plane. Finally, the theoretical problem of the HS velocity of growth is given an exact solution, in semiquantitative agreement with experiment.     

Immunoglobulin A antibodies to Helicobacter pylori

Serological testing for immunoglobulin G (IgG) antibodies to Helicobacter pylori has proven useful in supporting the diagnosis of infection with this organism, but the clinical value of IgA antibodies in H. pylori-related gastritis remains controversial. The purpose of our study was to determine the frequency of IgA-positive IgG-negative patients with symptoms of gastrointestinal (GI) disorders, thus assessing the clinical utility of IgA testing for H. pylori-related gastritis. It was found previously that the frequency of infected individuals in this category (IgA positive and IgG negative) is about 2%, but a large number of IgG-negative patients with GI disorders suggestive of H. pylori infection have not been investigated until now.