Long term laboratory column experiments to simulate bank filtration: Factors controlling removal of sulfamethoxazole

Microbial removal of the poorly degradable antibiotic sulfamethoxazole (SMX) from surface water was investigated in laboratory columns to identify critical factors for SMX removal during bank filtration, such as the substrate concentration, redox conditions and the availability of biodegradable DOC. About 60% of SMX at a start concentration of 0.25 μg/L in surface water were removed within 14 d of column passage under aerobic conditions while no removal occurred under anoxic conditions. The adaptation time was very long and was not completed after 2 years of operation. Adaptation was faster and SMX degradation was improved at an elevated concentration of SMX (4.5 μg/L) with 90% removal in 3.5 d under aerobic conditions. SMX removal was less effective under anoxic conditions (27% in 14 d) but increased again under anaerobic conditions (51% in 14 d). According to the half-lives for SMX determined from the column data (1-9 d aerobic, 49 d anoxic and 16 d anaerobic) it is essential to provide several weeks up to months of travel time in bank filtration to allow for the degradation of SMX, and likely, also for other poorly degradable compounds. Thus, the occurrence of SMX in groundwater samples does not indicate persistency of SMX but reflects insufficient residence time or unfavorable respective redox conditions. Adaptation times of years may also be required for new bank filtration sites to develop their full removal potential towards trace pollutants. Long operation time, a comparable concentration level and similar redox conditions as in the field appear to be essential to obtain realistic results with laboratory column experiments that can be transferred to real bank filtration sites.     

Cyclodextrin Aldehydes are Oxidase Mimics

Cyclodextrins containing 6‐aldehyde groups were found to catalyse oxidation of aminophenols in the presence of hydrogen peroxide. The catalysis followed Michaelis–Menten kinetics and is related to the catalysis previously observed with cyclodextrin ketones. A range of different cyclodextrin aldehydes were prepared containing one, two or more aldehydes at the primary rim (6‐positions) or a ethoxy‐2‐al or propoxy‐3‐al at the secondary rim. 2‐O‐ethoxy‐2‐al‐β‐cyclodextrin ( 22 ) was found to be the best catalyst. The aldehydes are in many cases better catalysts than the ketones, because of their powerful covalent binding of hydrogen peroxide.     

Learning latent actions to control assistive robots

Autonomous Robots - Assistive robot arms enable people with disabilities to conduct everyday tasks on their own. These arms are dexterous and high-dimensional; however, the interfaces people must...     

Interaction of kinetics and internal diffusion in complex catalytic three-phase reactions: Activity and selectivity in citral hydrogenation

Kinetics and mass transfer effects were studied for the complex catalytic liquid-phase hydrogenation in a semi-batch reactor, where finely dispersed and larger catalyst particles were used. Citral was used as a model molecule. The intrinsic kinetics was determined with crushed catalyst particles at and at pressures ranging from 10 to 40 bar. A kinetic model was proposed and successfully fitted to the experimental data. In order to elucidate the influence of internal diffusion on the selectivity and activity in complex reactions, citral hydrogenation was performed with larger catalyst pellets, in a pressurized autoclave equipped with a catalyst basket. As expected, the activity decreased with increasing catalyst particle size. The product distribution was shifted from the primary hydrogenation product (citronellal) to the fully hydrogenated end product (3,7-dimethyloctanol) as the catalyst particle size was increased. The concentrations of the secondary hydrogenation products were minor throughout the experiment. A complete reaction-diffusion model was developed for large pellets and complex reactions systems.     

Computational thinking and thinking about computing

Computational thinking will influence everyone in every field of endeavour. This vision poses a new educational challenge for our society, especially for our children. In thinking about computing, we need to be attuned to the three drivers of our field: science, technology and society. Accelerating technological advances and monumental societal demands force us to revisit the most basic scientific questions of computing.     

The dynamics of power in psychotherapy.

Feminist psychology has brought a renewed interest in the issue of power in the treatment relationship. Power as an important facet in psychotherapy is explored here particularly with regard to the conceptualization of power within the modality of treatment and with regard to the potential influence of stereotyping in the treatment relationship. Cognitions about power and stereotyping, like countertransference, are conceptualized as a dynamic force that may prescribe the power distribution and roles in the treatment relationship. These factors may operate outside the conscious awareness of either or both the therapist and the patient and may bias the clinical judgment of the therapist and/or undermine a patient's sense of empowerment. Practical solutions to deal with these dynamic forces are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Characterizing and Mining the Citation Graph of the Computer Science Literature

Citation graphs representing a body of scientific literature convey measures of scholarly activity and productivity. In this work we present a study of the structure of the citation graph of the computer science literature. Using a web robot we built several topic-specific citation graphs and their union graph from the digital library ResearchIndex. After verifying that the degree distributions follow a power law, we applied a series of graph theoretical algorithms to elicit an aggregate picture of the citation graph in terms of its connectivity. We discovered the existence of a single large weakly-connected and a single large biconnected component, and confirmed the expected lack of a large strongly-connected component. The large components remained even after removing the strongest authority nodes or the strongest hub nodes, indicating that such tight connectivity is widespread and does not depend on a small subset of important nodes. Finally, minimum cuts between authority papers of different areas did not result in a balanced partitioning of the graph into areas, pointing to the need for more sophisticated algorithms for clustering the graph.     

A Nitpick Analysis of Mobile IPv6

A lightweight formal method enables partial specification and automatic analysis by sacrificing breadth of coverage and expressive power. NP is a specification language that is a subset of Z, and Nitpick is a tool that quickly and automatically checks properties of finite models of systems specified in NP. We used NP to state two critical acyclicity properties of Mobile IPv6, a new internetworking protocol that allows mobile hosts to communicate with each other. In our Nitpick analysis of Mobile IPv6 we discovered a design flaw: one of the acyclicity properties does not hold. It takes only two hosts to exhibit this flaw. This paper gives self-contained overviews of Mobile IPv6 and of NP and Nitpick sufficient to understand the details of our specification and analysis. Received September 1997 / Accepted in revised form January 2000