Multicentre evaluation of the EBIO plus glucose analyser

The EBIO plus, a newly developed dedicated glucose analyser, was tested at three different sites for its analytical characteristics and practicability. Results were linear over a range of 2-50 mmol/l, precision was satisfactory (overall CV < 5.3% at a concentration level of 1.8 mmol/l and < 3.7% at a concentration level of 4.5-21 mmol/l). Calibration was stable up to 90 minutes. No significant influences were observed for several potential interfering substances at physiological or therapeutical levels. Practicability was found to be good. Sample through-put depends on calibration frequency and is maximally 166 per hour. Some problems with outliers had to be overcome in the beginning of the evaluation period, but in the end all evaluators concluded that the EBIO plus is user friendly with good analytical characteristics.     

Compact disc standards: an introductory overview

The success of the compact disc (CD) as a storage medium for digital audio has, over the last ten years, resulted in a number of initiatives to use the CD for other applications as well, e.g., as read-only memory for computers, as a storage medium for audio-visual material for multimedia applications, and as a storage medium for photographs. Each of these applications poses additional requirements on how the corresponding information is stored and retrieved, resulting in a range of different CD standards. The functional specifications of these standards are each given a specific color for ease of reference: the Red Book for CD-DA, the Yellow Book for CD-ROM, the Green Book for CD-I, etc. This paper aims at giving an overview of the various CD standards by explaining what is specified in each of the colored books and by indicating how they relate to one another.     

Comparison of methods for converting Dylos particle number concentrations to PM2.5 mass concentrations

The aim of this study was to (a) develop a method for converting particle number concentrations (PNC) obtained by Dylos to PM2.5 mass concentrations, (b) compare this conversion with similar methods available in the literature, and (c) compare Dylos PM2.5 obtained using all available conversion methods with gravimetric samples. Data were collected in multiple residences in three European countries using the Dylos and an Aerodynamic Particle Sizer (APS, TSI) in the Netherlands or an optical particle counter (OPC, GRIMM) in Greece. Two statistical fitted curves were developed based on Dylos PNC and either an APS or an OPC particle mass concentrations (PMC). In addition, at the homes of 16 volunteers (UK and Netherlands), Dylos measurements were collected along with gravimetric samples. The Dylos PNC were transformed to PMC using all the fitted curves obtained during this study (and three found in the literature) and were compared with gravimetric samples. The method developed in the present study using an OPC showed the highest correlation (Pearson (R) = 0.63, Concordance (ρ_c) = 0.61) with gravimetric data. The other methods resulted in an underestimation of PMC compared to gravimetric measurements (R = 0.65‐0.55, ρ_c = 0.51‐0.24). In conclusion, estimation of PM2.5 concentrations using the Dylos is acceptable for indicative purposes.     

Intermittent operation of ultra-low pressure ultrafiltration for decentralized drinking water treatment

River water was treated by ultrafiltration at a relatively low transmembrane pressure (40 mbar). As observed before, flux stabilization occurred after several days of operation although no back-flushing or cross flow was applied. Interruptions in flux were applied by temporary offset of the transmembrane pressure. After restoration of the transmembrane pressure, the initial flux was higher than the stable flux level, and the flux recovery depended on the standstill time. Furthermore, if a short cross flow was applied after standstill, the flux was restored to an even higher level. In all cases, the flux decreased again during operation to reach finally the same stable level as before standstill. In order to evaluate the influence of intermittent operation as practiced for water treatment on a household level, daily interruptions of flux were applied. An optimum of total daily water production rate was obtained at 21 h of operation and 3 h of standstill per day. A model was developed which can describe the impact of intermittent operation on the flux depending on the duration of the standstill and operating periods. This enables the prediction of production capacity of the system operated intermittently. The flux increase during standstill could be explained by a relaxation and expansion of the biofouling layer, while the higher flux after forward-flushing was caused by this layer being partially sloughed off. Household water treatment with the process presented here will generally be operated on a discontinuous basis. The results show that such operation schemes do not compromise the permeability of the system, but actually lead to higher fluxes after standstill.     

Ammonium adsorption in aerobic granular sludge, activated sludge and anammox granules

The ammonium adsorption properties of aerobic granular sludge, activated sludge and anammox granules have been investigated. During operation of a pilot-scale aerobic granular sludge reactor, a positive relation between the influent ammonium concentration and the ammonium adsorbed was observed. Aerobic granular sludge exhibited much higher adsorption capacity compared to activated sludge and anammox granules. At an equilibrium ammonium concentration of 30 mg N/L, adsorption obtained with activated sludge and anammox granules was around 0.2 mg NH₄-N/g VSS, while aerobic granular sludge from lab- and pilot-scale exhibited an adsorption of 1.7 and 0.9 mg NH₄-N/g VSS, respectively. No difference in the ammonium adsorption was observed in lab-scale reactors operated at different temperatures (20 and 30 °C). In a lab-scale reactor fed with saline wastewater, we observed that the amount of ammonium adsorbed considerably decreased when the salt concentration increased. The results indicate that adsorption or better ion exchange of ammonium should be incorporated into models for nitrification/denitrification, certainly when aerobic granular sludge is used.     

Natural skin surface pH is on average below 5, which is beneficial for its resident flora

Variable skin pH values are being reported in literature, all in the acidic range but with a broad range from pH 4.0 to 7.0. In a multicentre study (N = 330), we have assessed the skin surface pH of the volar forearm before and after refraining from showering and cosmetic product application for 24 h. The average pH dropped from 5.12 +/- 0.56 to 4.93 +/- 0.45. On the basis of this pH drop, it is estimated that the 'natural' skin surface pH is on average 4.7, i.e. below 5. This is in line with existing literature, where a relatively large number of reports (c. 50%) actually describes pH values below 5.0; this is in contrast to the general assumption, that skin surface pH is on average between 5.0 and 6.0. Not only prior use of cosmetic products, especially soaps, have profound influence on skin surface pH, but the use of plain tap water, in Europe with a pH value generally around 8.0, will increase skin pH up to 6 h after application before returning to its 'natural' value of on average below 5.0. It is demonstrated that skin with pH values below 5.0 is in a better condition than skin with pH values above 5.0, as shown by measuring the biophysical parameters of barrier function, moisturization and scaling. The effect of pH on adhesion of resident skin microflora was also assessed; an acid skin pH (4-4.5) keeps the resident bacterial flora attached to the skin, whereas an alkaline pH (8-9) promotes the dispersal from the skin.     

What it takes to forgive: When and why executive functioning facilitates forgiveness.

To establish what it takes to forgive, the present research focused on the cognitive underpinnings of the forgiveness process. We conducted four studies that examined and supported the prediction that executive functioning (a set of cognitive control processes) facilitates forgiveness. First, a correlational study revealed a positive relation between executive functioning and dispositional forgiveness (Study 1). Second, a longitudinal study demonstrated that executive functioning predicts the development of forgiveness over a period of 5 weeks after the offense (Study 2). Finally, two experiments examined when and why executive functioning facilitates forgiveness. Specifically, and in line with predictions, Studies 3 and 4 showed that executive functioning facilitates forgiveness only in the case of relatively severe (as compared with mild) offenses. Furthermore, Study 4 provided evidence for a psychological mechanism underlying the relation between executive functioning and forgiveness by demonstrating the mediating role of rumination about the offense. Implications of these findings for the literature on forgiveness and the role of executive functioning in interpersonal relationships more generally are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Functional analysis of structural genes for NAD(+)-dependent formate dehydrogenase in Saccharomyces cerevisiae

Co-consumption of formate by aerobic, glucose-limited chemostat cultures of Saccharomyces cerevisiae CEN.PK 113-7D led to an increased biomass yield relative to cultures grown on glucose as the sole carbon and energy substrate. In this respect, this strain differed from two previously investigated S. cerevisiae strains, in which formate oxidation did not lead to an increased biomass yield on glucose. Enzyme assays confirmed the presence of a formate-inducible, cytosolic and NAD(+)-dependent formate dehydrogenase. To investigate whether this enzyme activity was entirely encoded by the previously reported FDH1 gene, an fdh1Delta null mutant was constructed. This mutant strain still contained formate dehydrogenase activity and remained capable of co-consumption of formate. The formate dehydrogenase activity in the mutant was demonstrated to be encoded by a second structural gene for formate dehydrogenase (FDH2) in S. cerevisiae CEN.PK 113-7D. FDH2 was highly homologous to FDH1 and consisted of a fusion of two open reading frames (ORFs) (YPL275w and YPL276w) reported in the S. cerevisiae genome databases. Sequence analysis confirmed that, in the database genetic background, the presence of two single-nucleotide differences led to two truncated ORFs rather than the full-length FDH2 gene present in strain CEN.PK 113-7D. In the latter strain background an fdh1Deltafdh2Delta double mutant lacked formate dehydrogenase activity and was unable to co-consume formate. Absence of formate dehydrogenase activity did not affect growth on glucose as sole carbon source, but led to a reduced biomass yield on glucose-formate mixtures. These findings are consistent with a role of formate dehydrogenase in the detoxification of exogenous formate.     

Nanoarrays: a method for performing enzymatic assays

Conventional enzymatic assays for alcohol dehydrogenase, pyruvate kinase, and enolase performed in 96-well microtiter plates were compared with assays monitored in 25-well nanoarrays. All miniaturized reactions could be performed in maximum volumes of 6.3-8 nL and were read out with a conventional fluorescence microscope system equipped with a scientific grade CCD camera. Substrate and cofactor were already present inside the wells after having been presprayed, or they were applied in solution to the wells of the nanoarray shortly before the assays started. For all of the assays, commercially available enzymes and enzymes present in cell-free extracts were used. Assays carried out in premixed nanoarrays gave results comparable to those performed in presprayed nanoarrays. Enzyme activities determined in nanoarrays by using two different methods were in good agreement with assays performed in microtiter plates. Also, good correspondence was found between expected and observed enzyme levels. In short, enzymatic assays performed in premixed and in particular in presprayed nanoarrays are a promising low-volume and low-reagent- and sample-consuming alternative to current methodology and could find applications in many different areas of analytical chemistry.     

Pyruvate decarboxylase: An indispensable enzyme for growth of Saccharomyces cerevisiae on glucose

In Saccharomyces cerevisiae, the structural genes PDC1, PDC5 and PDC6 each encode an active pyruvate decarboxylase. Replacement mutations in these genes were introduced in a homothallic wild-type strain, using the dominant marker genes APT1 and Tn5ble. A pyruvate-decarboxylase-negative (Pdc⁻) mutant lacking all three PDC genes exhibited a three-fold lower growth rate in complex medium with glucose than the isogenic wild-type strain. Growth in batch cultures on complex and defined media with ethanol was not impaired in Pdc⁻ strains. Furthermore, in ethanol-limited chemostat cultures, the biomass yield of Pdc⁻ and wild-type S. cerevisiae were identical. However, Pdc⁻ S. cerevisiae was unable to grow in batch cultures on a defined mineral medium with glucose as the sole carbon source. When aerobic, ethanol-limited chemostat cultures (D = 0·10 h⁻¹) were switched to a feed containing glucose as the sole carbon source, growth ceased after approximately 4 h and, consequently, the cultures washed out. The mutant was, however, able to grow in chemostat cultures on mixtures of glucose and small amounts of ethanol or acetate (5% on a carbon basis). No growth was observed when such cultures were used to inoculate batch cultures on glucose. Furthermore, when the mixed-substrate cultures were switched to a feed containing glucose as the sole carbon source, wash-out occurred. It is concluded that the mitochondrial pyruvate dehydrogenase complex cannot function as the sole source of acetyl-CoA during growth of S. cerevisiae on glucose, neither in batch cultures nor in glucose-limited chemostat cultures.