Scanning tunneling microscopy study of thin PTCDI films on Ag/Si(111)-√3 × âˆš3.

3,4,9,10-perylene tetracarboxylic diimide molecules were evaporated onto a Ag/Si(111)-√3 × âˆš3 surface and studied by scanning tunneling microscopy/spectroscopy and low energy electron diffraction (LEED). The growth mode was characterized as layer-by-layer growth with a single molecular unit cell in a short range order. The growth of the first two monolayers involves a molecule/substrate superstructure and a molecule/molecule superstructure. At higher coverages, the molecules in each layer were found to align so that unit cells are on top of each other. The experimentally obtained LEED pattern is described as a combination of patterns from the molecular unit cell and the molecule/substrate superstructure. The electronic structure was found to be strongly dependent on the film thickness for the first few layers: Several extra states are found at low coverages compared to higher coverages resulting in a very small pseudo gap of 0.9 eV for the first layer, which widens up to 4.0 eV for thicker films.

Contaminants in organically and conventionally produced winter wheat (Triticum aestivum) in Belgium.

A database has been compiled with the levels of important contaminants (mycotoxins, heavy metals and pesticides) measured from 2002 to 2005 in winter wheat (Triticum aestivum) grown in Belgium according to the organic and conventional farming systems. Assuming no further change in contaminant levels during cereal processing and during the preparation of foodstuffs, conservative intakes are estimated for the consumers of cereal-based products such as flour, bread, breakfast cereals, dough and pastry. The results show that for the consumer of organic foodstuffs, estimated daily intakes are 0.56 microg deoxynivalenol (DON), 0.03 microg zearalenone (ZEA), 0.19 microg Cd, 0.28 microg Pb and 0.0006 microg Hg kg(-1) body weight, taking into account the average contaminant levels in unprocessed grains and the average cereal products consumptions in Belgium. For the consumers of conventional foodstuffs, the corresponding estimated daily intakes are 0.99 microg DON, 0.06 microg ZEA, 0.17 microg Cd, 0.12 microg Pb and 0.0007 microg Hg kg(-1) body weight. In addition, it appears that for the consumers of conventional products, intakes of some post-harvest insecticides have to be taken into account (0.11 microg chlorpyriphos-methyl, 0.2 microg dichlorvos and 0.24 microg pirimiphos-methyl kg(-1) bw). When expressed as a percentage of the tolerable/acceptable daily intake (TDI/ADI), it seems that the corresponding estimated (conservative) intakes are the highest for DON (56% for organic and 99% for conventional cereal products), ZEA (16% for organic and 32% for conventional cereal products), and Cd (19% for organic and 17% for conventional cereal products), all other estimated intakes of contaminants (including pesticides) being lower than 10% of the TDI/ADI.

Intake of ochratoxin A and deoxynivalenol through beer consumption in Belgium.

Estimations of ochratoxin A (OTA) and 4-deoxynivalenol (DON) exposure of the Belgian population through beer consumption were made using the results of the recent Belgian food survey and the compiled data set of OTA and DON levels in conventionally and organically produced beers in 2003-05. For the consumers of organic beers, the daily intake of OTA was 0.86 (in 2003), 1.76 (in 2004) and 0.72 (in 2005) ng kg(-1) body weight (bw), considering the mean beer consumption (0.638 litres) and the average level of OTA in 2003, 2004 and 2005, respectively. Using the 97.5th percentile of beer consumption (1.972 litres), the corresponding OTA daily intakes were 2.65, 5.44 and 2.24 ng kg(-1) bw, which are close or above the tolerable daily intake (TDI) of 5 ng kg(-1) bw. For the consumers of conventional beers, the OTA intakes were low: 0.23, 0.23 and 0.11 ng kg(-1) bw day(-1) for the average beer consumption, in 2003, 2004 and 2005 against 0.72, 0.73 and 0.34 ng kg(-1) bw day(-1) when the 97.5th percentile level was considered. As for the DON intake, the estimates were quite low for both conventional and organic beer consumers when the provisional maximum TDI (PMTDI) of 1 microg kg(-1) bw was considered. Average consumption of organic beer led to daily intakes of 0.05 and 0.04 microg DON kg(-1) bw in 2003 and 2004, respectively, whilst for conventional beer, daily intakes were 0.07 and 0.05 microg DON kg(-1) bw. At the 97.5th percentile level of beer consumption, daily intakes of 0.15 and 0.13 microg kg(-1) bw were obtained for organic beers against 0.23 and 0.17 microg kg(-1) bw for conventional ones. The results showed that beer could be an important contributor to OTA exposure in Belgium, even though a declining trend seems to be apparent during the last year of monitoring. Therefore, efforts should be devoted to maintain the OTA levels as low as reasonably achievable, especially for organic beer.

Risk assessment of dietary acrylamide intake in Flemish adolescents.

Acrylamide has recently been found in a range of heat treated food items. As it is a neurotoxic agent and a probable, human carcinogen (IARC 2A), human exposure to this chemical might constitute an important public health issue. The purpose of the study was to estimate the acrylamide intake in Flemish adolescents (based on 7-day food record) and to evaluate the possible health risks due to the exposure. The Belgian Federal Agency for the Safety of the Food Chain collected 150 food items from different supermarkets and restaurants to analyse the acrylamide level. The limit of quantitation was 30 microg acrylamide/kg foodstuffs. Exposure modelling was based on Monte Carlo simulations. The estimated dietary intake of acrylamide per person given as the 5th, 50th and 95th percentile were 0.19, 0.51 and 1.09 mircog/kg bw/d. Bread, despite its low acrylamide content, is relevant as a source of acrylamide exposure at the lower percentiles. At higher percentiles the contribution of French fries and crisps is more important. It must be emphasised that the exposure assessment has several limitations. Risk of neurotoxicity seems negligible. The relevance of current intake levels in terms of cancer risk remains a subject of debate.

A tree based lack-of-fit test for multiple logistic regression.

Several omnibus tests have been developed to assess the fit of a regression model. But many of these lack-of-fit tests focus on the simple regression setting. Here, we focus on multiple logistic regression. Pearson's well-known chi-square test statistic and the deviance statistic are no longer valid in the case that the model contains one or more continuous covariates. To overcome this difficulty, Hosmer and Lemeshow proposed a Pearson type statistic based on groups defined by the so-called deciles of risk. We propose a test statistic that is similar in approach to the Hosmer and Lemeshow statistic in that the observations are classified into distinct groups. In the procedure proposed here however, the grouping is not according to probabilities fitted under the null model. We use a recursive partitioning algorithm to divide the sample space into different groups. This generally allows for a more powerful assessment of the model fit. Simulations are carried out to compare the results of the proposed test to that of Hosmer and Lemeshow. Three data examples illustrate the performance of the tree based lack-of-fit test, in comparison to several other tests.

Self-organized discotic liquid crystals for high-efficiency organic photovoltaics.

Self-organization of liquid crystalline and crystalline-conjugated materials has been used to create, directly from solution, thin films with structures optimized for use in photodiodes. The discotic liquid crystal hexa-peri-hexabenzocoronene was used in combination with a perylene dye to produce thin films with vertically segregated perylene and hexabenzocoronene, with large interfacial surface area. When incorporated into diode structures, these films show photovoltaic response with external quantum efficiencies of more than 34 percent near 490 nanometers. These efficiencies result from efficient photoinduced charge transfer between the hexabenzocoronene and perylene, as well as from effective transport of charges through vertically segregated perylene and hexabenzocoronene pi systems. This development demonstrates that complex structures can be engineered from novel materials by means of simple solution-processing steps and may enable inexpensive, high-performance, thin-film photovoltaic technology.

[Trends in mortality and morbidity among the elderly in The Netherlands, 1970-1989]. / De ontwikkeling van mortaliteit en morbiditeit onder ouderen in Nederland, 1970-1989.

OBJECTIVE: Analysis of the trends in mortality and morbidity among the elderly to see whether there has been a 'compression' of mortality and morbidity in the older age groups during the past two decades. METHOD: Data on mortality (by age, sex and cause of death; 55-84 years; 1970-1989), hospital admissions (by age, sex and discharge diagnosis; 55-84 years; 1972-1987) and self-reported morbidity (65+ years) were extracted from publications by the Netherlands Central Bureau of Statistics, and analysed on an age-specific and age-standardised basis. RESULTS: A decline in mortality for men and women was seen in all age groups between 1970 and 1989. Diseases of 'circulatory organs' and 'accidents and intoxications' accounted for the major part. In contrast, hospital admission rates increased for men and women in all age groups between 1972 and 1987, mainly due to diseases of 'circulatory organs' and 'neoplasms'. No correlation was found between decline of mortality and increase of hospital admissions per disease cluster. Questionnaire data revealed no major changes in health problems. CONCLUSION: Whereas mortality declined in all age groups, hospital admissions rose, and prevalence rates of self-reported health problems remained essentially the same. We conclude that there has probably been a compression of neither mortality nor morbidity during the past two decades in the Netherlands.

The dependence of electron transfer efficiency on the conformational order in organic monolayers.

The electron transfer through an organized organic monolayer of alkyl chains adsorbed on a silicon wafer has been studied. The silicon was used as an electrode in a three-electrode electrochemical cell, and the current versus voltage response was measured. The results show that when the chains in the monolayer are in the "all trans" configuration, the charge transfer efficiency is higher than when the chains have a "gauche" configuration. A mechanism rationalizing all the observations is suggested.