An interlaboratory study as useful tool for proficiency testing of chemical oxygen demand measurements using solid substrates and liquid samples with high suspended solid content

In 2008, the first Proficiency Testing Scheme of Chemical Oxygen Demand (1^stCOD-PT^ADG) was conducted to assess the results obtained for different research groups whose field work is mainly anaerobic digestion. This study was performed using four samples, two solid samples as raw materials and two solid samples to prepare high concentration suspended solid solutions. Invitations were sent to a large number of laboratories, mainly to anaerobic digestion research groups. Finally, thirty labs from sixteen countries agreed to participate, but for different reasons four participants could not send any data. In total, twenty-six results were reported to the COD-PT coordinator.This study showed the importance of continuous participation in proficiency testing (PT) schemes in order to compare the results obtained. Taking into account the lack of a general standard method and high quality certified reference materials (CRMs), the traceability of COD determination is not currently easy to check. In addition, the spread of participants’ results obtained was high and pointed to the advisability of using consensus values due to their unreliability. Therefore, the theoretical oxygen demand (ThOD) values were considered as assigned values for all the samples analysed. On the other hand, in this PT the established standard deviation (ESD) has been determined by the Horwitz modified function.Participants of this 1^stCOD-PT^ADG were asked to give a short report on the analytical method used. Although all the participants used potassium dichromate as their oxidant reagent, their experimental procedures were very different. With the purpose of comparing the results obtained, the different experimental conditions used were classified into five methods, corresponding to two main categories, open and closed reflux. The performance of laboratories was expressed by the z-score, whose value is considered satisfactory when z-score ≤±2. The overall analytical data evaluation showed that 64% of z-scores obtained were outside the accepted limits.     

Driving matrix liquid crystal displays

Liquid crystal displays had a humble beginning with wrist watches in the seventies. Continued research and development in this multi-disciplinary field have resulted in displays with increased size and complexity. After three decades of growth in performance, LCDs now offer a formidable challenge to the cathode ray tubes (CRT). A major contribution to the growth of LCD technology has come from the developments in addressing techniques used for driving matrix LCDs. There are several approaches like passive matrix addressing, active matrix addressing and plasma addressing to drive a matrix display. Passive matrix LCD has a simple construction and uses the intrinsic non-linear characteristic of the LCD for driving. Departure from conventional line by line addressing of a passive matrix has resulted in improved performance of the display. Orthogonal functions have played a crucial role in the development of passive matrix addressing. Simple orthogonal functions that are useful for driving a matrix LCD are introduced. The basics of driving several rows simultaneously (multi-line addressing) are discussed by drawing analogies from multiplexing in communication. The impact of multi-line addressing techniques on the performance of the passive matrix LCDs in comparison with the conventional technique will be discussed.     

On the governing equations for the compressing process and its coupling with other processes

As a continuation of a recent linear analysis by Mao et al.(Acta Mech Sin,2010,26:355),in this paper we propose a general theoretical formulation for the compressing process in complex Newtonian fluid flows,which covers gas dynamics,aeroacoustics,nonlinear thermoviscous acoustics,viscous shock layer,etc.,as its special branches.The principle on which our formulation is based is the maximally natural and dynamic Helmholtz decomposition of the Navier-Stokes equation,along with the kinematic Helmholtz decompos...     

Evaluating the interactions of vertebrate receptors with persistent pollutants and antifouling pesticides using recombinant yeast assays

The development of in vitro methods for screening potentially harmful biological activities of new compounds is an extremely important way to increase not only their intrinsic environmental safety, but also the public perception of the safety standards associated with them. In this work we use two yeast systems to test the ability of different chemicals to bind and activate two vertebrate receptors which are intimately related to adverse biological effects of pollution in exposed fauna: the estrogen receptor (ER) and the aryl hydrocarbon receptor (AhR). The panel of compounds analysed here includes well-known pollutants, like PCBs, pp′-DDT and hexachlorobenzene, together with the less-known, emerging putative pollutants, such as Sea-Nine, Irgarol and diuron. Results show the ability of some of these compounds to interact with one or both receptors, provide hints about the relationship between structure and activity, and suggest mechanistic explanations for the biological activities already described in whole-animal experiments. In addition, we show that AhR may have an intrinsic ligand promiscuity comparable to that of ER, a feature not fully appreciated in the past due to the technical difficulties involved with testing highly lipophilic substances in yeast-based assays.     

Toxicity identification fractionation of environmental estrogens in waste water and sludge using gas and liquid chromatography coupled to mass spectrometry and recombinant yeast assay

We developed a toxicity identification fractionation (TIF) procedure to determine estrogenic compounds in wastewaters and sludge. The procedure consisted in fractionation of samples through a C₁₈ solid-phase extraction cartridge, in which Fraction I contained nonylphenol (NP) and its mono (NPEO₁) and diethoxylate (NPEO₂) and the markers of faecal exposure, Fraction II contained bisphenol A (BPA) and synthetic and natural hormones, and Fraction III contained the hormone conjugates. These three fractions were analyzed in parallel using gas or liquid chromatography coupled to mass spectrometry and recombinant yeast assay (RYA). Water samples collected daily throughout a whole week contained from 0.45 to 7.22 μg L⁻¹ of NP > NPEO₁ > NPEO₂ and were responsible for the estrogenicity of these samples. Fractions II and III were not estrogenic and that was due to the low ng L⁻¹ level of hormones and hormone conjugates found, respectively. The biological treatment sewage treatment plant (STP) was capable to eliminate from 52 to 100% of the compounds, with bisphenol A being the least removed. Only alkylphenols were accumulated in sludge with concentrations from 8.69 to 26.3 mg kg⁻¹ dw of NPEO₁ > NPEO₂ > NP. The integrated procedure herein proposed can be used as a screening method to evaluate estrogenic compounds in STPs and to survey faecal elimination.