Kinetics and mechanistic aspects of As(III) oxidation by aqueous chlorine, chloramines, and ozone: relevance to drinking water treatment

Kinetics and mechanisms of As(III) oxidation by free available chlorine (FAC-the sum of HOCl and OCl-), ozone (O3), and monochloramine (NH2Cl) were investigated in buffered reagent solutions. Each reaction was found to be first order in oxidant and in As(III), with 1:1 stoichiometry. FAC-As(III) and O3-As(III) reactions were extremely fast, with pH-dependent, apparent second-order rate constants, k'app, of 2.6 (+/- 0.1) x 10(5) M(-1) s(-1) and 1.5 (+/- 0.1) x 10(6) M(-1) s(-1) at pH 7, whereas the NH2Cl-As(III) reaction was relatively slow (k'app = 4.3 (+/- 1.7) x 10(-1) M(-1) s(-1) at pH 7). Experiments conducted in real water samples spiked with 50 microg/L As(III) (6.7 x 10(-7) M) showed that a 0.1 mg/L Cl2 (1.4 x 10-6 M) dose as FAC was sufficient to achieve depletion of As(III) to <1 microg/L As(III) within 10 s of oxidant addition to waters containing negligible NH3 concentrations and DOC concentrations <2 mg-C/L. Even in a water containing 1 mg-N/L (7.1 x 10(-5) M) as NH3, >75% As(III) oxidation could be achieved within 10 s of dosing 1-2 mg/L Cl2 (1.4-2.8 x 10(-5) M) as FAC. As(III) residuals remaining in NH3-containing waters 10 s after dosing FAC were slowly oxidized (t1/2 > or = 4 h) in the presence of NH2Cl formed by the FAC-NH3 reaction. Ozonation was sufficient to yield >99% depletion of 50 microg/L As(III) within 10 s of dosing 0.25 mg/L O3 (5.2 x 10(-6) M) to real waters containing <2 mg-C/L of DOC, while 0.8 mg/L O3 (1.7 x 10(-5) M) was sufficientfor a water containing 5.4 mg-C/L of DOC. NH3 had negligible effect on the efficiency of As(III) oxidation by O3, due to the slow kinetics of the O3-NH3 reaction at circumneutral pH. Time-resolved measurements of As(III) loss during chlorination and ozonation of real waters were accurately modeled using the rate constants determined in this investigation.     

Hexabromocyclododecanes (HBCDs) in the environment and humans: a review

Hexabromocyclododecanes (HBCDs) are brominated aliphatic cyclic hydrocarbons used as flame retardants in thermal insulation building materials, upholstery textiles, and electronics. As a result of their widespread use and their physical and chemical properties, HBCDs are now ubiquitous contaminants in the environment and humans. This review summarizes HBCD concentrations in several environmental compartments and analyzes these data in terms of point sources versus diffuse sources, biomagnification potential, stereoisomer profiles, time trends, and global distribution. Generally, higher concentrations were measured in samples (air, sediment, and fish) collected near point sources (plants producing or processing HBCDs), while lower concentrations were recorded in samples from locations with no obvious sources of HBCDs. High concentrations were measured in top predators, such as marine mammals and birds of prey (up to 9600 and 19 200 ng/g lipid weight, respectively), suggesting a biomagnification potential for HBCDs. Relatively low HBCD concentrations were reported in the few human studies conducted to date (median values varied between 0.35 and 1.1 ng/g lipid weight). HBCD levels in biota are increasing slowly and seem to reflect the local market demand. One important observation is the shiftfrom the high percentage of the gamma-HBCD stereoisomer in the technical products to a dominance of the alpha-HBCD stereoisomer in biological samples. A combination of factors such as variations in solubility, partitioning behavior, uptake, and, possibly, selective metabolism of individual isomers may explain the observed changes in stereoisomer patterns. Recommendations for further work include research on how HBCDs are transferred from products into the environment upon production, use, and disposal. Time trends need to be analyzed more in detail, including HBCD stereoisomers, and more data on terrestrial organisms are needed, especially for humans. Whenever possible, HBCDs should be analyzed as individual stereoisomers in order to address their fate and effects.     

Romanian River Basins Lag Time Analysis. The SCS-CN Versus RNS Comparative Approach Developed for Small Watersheds

Romanian policy makers have to perceive that human intervention on river basins land cover is influencing rainfall-runoff relation and the used methodology cannot accurately estimate watershed surface flow transformations. Global water cycles and energy fluxes understanding is leading to better predictions of land atmosphere interaction and local hydro-climates evolution. The water transfer time determination from rainfall to runoff needs accurate measurements of river basins hydrological parameters. Here, we analyzed and compared the lag time value results of two different methodologies (curve number and rational methodology) used for 54 Romanian small catchment areas study. The focus of this paper is the lag time evaluation and interpretation for an effective implementation of the best methodology approach in the Romanian geographical space. Our research in small river basins was developed using remote sensing technology maps, GIS and environmental datasets in combination with field work on every drainage basin in order to assess the specific morphological features and validate the land cover typology. We found that Soil Conservation Service - Curve Number (SCS-CN) method is widely used according to USA landscape features classification, but not necessarily applicable to Romanian river basins characteristics. Our results show how the official Romanian rational methodology national standard (RNS) can be improved and the limits of SCS-CN method.

     

Real-time three-dimensional wind simulation for windmill rig tests

This paper deals with the methods of three-dimensional fixed-point wind speed real-time simulation modelled in large band, in order to use them in test rigs for experimental investigation of the wind energy conversion systems. The medium- and long-term components of the non-stationary wind speed are considered as known, being issued from measured data or by adopting a generic model. The spectral characteristics of three-dimensional turbulence are described either by the Kaimal or the von Karman models. The turbulence intensity and the length scale that take part in these models are calculated by the site parameters, using current standards. The basic idea of the methods for large-band three-dimensional wind simulation is to use rational shaping filters that approximate non-integer orders shaping filters issued from the Kaimal and the von Karman models. All the synthesized rational shaping filters use one time constant, automatically adapted to the medium- and long-term components that pilot the other time constants of the shaping filters by a set of parameters practically constant. Some numerical results concerning time series that simulate the non-stationary wind speed with three-dimensional turbulence components based on Kaimal and von Karman models are presented.     

La CLAve to increase psychosis literacy of Spanish-speaking community residents and family caregivers.

The authors developed and tested a 35-min psychoeducational program with the goal of increasing Spanish-speaking persons’ literacy of psychosis. The program uses popular cultural icons derived from music, art, and videos, as well as a mnemonic device—La CLAve (The Clue)—to increase (a) knowledge of psychosis, (b) efficacy beliefs that one can identify psychosis in others, (c) attributions to mental illness, and (d) professional help-seeking. Assessments were conducted before and after administering the program to both community residents (n = 57) and family caregivers of persons with schizophrenia (n = 38). For community residents, the authors observed increases across the 4 domains of symptom knowledge, efficacy beliefs, illness attributions, and recommended help-seeking. For caregivers, increases were observed in symptom knowledge and efficacy beliefs. La CLAve is a conceptually informed psychoeducational tool with a developing empirical base aimed at helping Spanish-speaking Latinos with serious mental illness obtain care in a timely manner. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Onset of convection in a horizontal porous layer driven by catalytic surface reaction on the lower wall

The onset of convection in a horizontal layer filled with a fluid-saturated porous medium is studied in this paper. On the lower wall there is an exothermic surface reaction, described by the Arrhenius kinetics, while the upper wall is subjected to uniform temperature and concentration. The problem, cast in dimensionless form, is governed by three dimensionless parameters pertaining to the exothermic reaction and the Lewis number. Once the basic state is solved, a linearized stability analysis is then performed and the resulting eigenvalue problem is solved using a conventional shooting method. One determines numerically the critical Rayleigh and wave numbers at the onset of convection, for various values of the problem parameters.     

Ischemic modulation of vulnerable period and the effects of pharmacological treatment of ischemia-induced arrhythmias: a simulation study

First identified in the 1930s (Ferris et al., 1936 and Wiggers and Wegria, 1939), the concept of vulnerability applies perfectly to biological oscillators. We can safely say that vulnerability is an inherent property of any excitable media. The duration of vulnerable period (VP) (the time interval during which single stimuli can initiate self-sustaining propagation) is sensitive to medium properties and stimulus parameters (stimulus field, timing behind the conditioning wave, and stimulus amplitude). Apart from medium properties and stimulus characteristics, heart vulnerability is affected by any intervention targeting the excitatory and recovery process. Therefore, we can expect that any pathological condition disturbing heart excitation or tissue recovery will most probably alter the duration of VP. In this paper, we shall explore the implications of ischemia and one of the arrhythmia counteracting methods widely used in clinical practice-antiarrhythmic drugs--in changing the boundaries of VP. The Cardiac Arrhythmia Suppression Trial (CAST) studies, as well as classification based on functional characteristics, revealed the arrhythmogenic potential of both Class I and Class III agents, but failed to identify the proarrhythmic mechanisms. This study presents results from a mathematical model (Cimponeriu et al., 2001) of the ventricle based on Luo-Rudy cellular formulation Luo and Rudy, 1991) modified for studying the ischemic modulation of VP and the effects of pharmacological treatment of ischemia-induced arrhythmia. Simulations revealed the link between the cellular antiarrhythmic properties and the proarrhythmic effect at the multicellular level in the case of Na+ channel blockade. Na+ channel blockade delayed recovery of cellular excitability, but also introduced a nonuniform dispersion of refractoriness along the cardiac fiber that can serve as a substrate for initiating a new arrhythmia. Our initial analysis proved that fast unbinding rates are essential in reducing the proarrhythmic potential of Class I drugs. However, further investigations led us to believe that binding properties are equally important. An antiarrhythmic drug with high affinity for drug-channel complex formation elicits a higher level of blockade per time unit. Under this light, we hypothesize that even the modern, fast unbinding drugs are not necessarily safe.     

The Role of 3-D Sound in Human Reaction and Performance in Augmented Reality Environments

Three-dimensional sound's effectiveness in virtual reality (VR) environments has been widely studied. However, due to the big differences between VR and augmented reality (AR) systems in registration, calibration, perceptual difference of immersiveness, navigation, and localization, it is important to develop new approaches to seamlessly register virtual 3-D sound in AR environments and conduct studies on 3-D sound's effectiveness in AR context. In this paper, we design two experimental AR environments to study the effectiveness of 3-D sound both quantitatively and qualitatively. Two different tracking methods are applied to retrieve the 3-D position of virtual sound sources in each experiment. We examine the impacts of 3-D sound on improving depth perception and shortening task completion time. We also investigate its impacts on immersive and realistic perception, different spatial objects identification, and subjective feeling of "human presence and collaboration". Our studies show that applying 3-D sound is an effective way to complement visual AR environments. It helps depth perception and task performance, and facilitates collaborations between users. Moreover, it enables a more realistic environment and more immersive feeling of being inside the AR environment by both visual and auditory means. In order to make full use of the intensity cues provided by 3-D sound, a process to scale the intensity difference of 3-D sound at different depths is designed to cater small AR environments. The user study results show that the scaled 3-D sound significantly increases the accuracy of depth judgments and shortens the searching task completion time. This method provides a necessary foundation for implementing 3-D sound in small AR environments. Our user study results also show that this process does not degrade the intuitiveness and realism of an augmented audio reality environment     

Recognition is not parsing — SPPF-style parsing from cubic recognisers

In their recogniser forms, the Earley and RIGLR algorithms for testing whether a string can be derived from a grammar are worst-case cubic on general context free grammars (CFG). Earley gave an outline of a method for turning his recognisers into parsers, but it turns out that this method is incorrect. Tomita’s GLR parser returns a shared packed parse forest (SPPF) representation of all derivations of a given string from a given CFG but is worst-case unbounded polynomial order. The parser version of the RIGLR algorithm constructs Tomita-style SPPFs and thus is also worst-case unbounded polynomial order. We have given a modified worst-case cubic GLR algorithm, that, for any string and any CFG, returns a binarised SPPF representation of all possible derivations of a given string. In this paper we apply similar techniques to develop worst-case cubic Earley and RIGLR parsing algorithms.