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The causes of soil water repellency are still only poorly understood. It is generally assumed that hydrophobic organic compounds are responsible, but those concerned have not previously been identified by comparison between samples taken from a water repellent topsoil and the wettable subsoil. In this study we separated, characterised, and compared the organic compounds present at 4 different depths in a sandy soil under permanent grass cover that is water repellent in the upper 0.30 m but wettable below this. Soil samples were extracted using a mixture of isopropanol and aqueous ammonia (7:3 v : v). Samples were wettable after extraction and re-application of the extract from each sample onto wettable sand induced water repellency. The chloroform-soluble portions of the extracts were analysed by gas chromatography and gas chromatography-mass spectrometry. The compounds identified at all soil depths included long-chain carboxylic acids ([C.sub.16]-[C.sub.24]), amides ([C.sub.14]-[C.sub.24]), alkanes ([C.sub.25]-[C.sub.31]), aldehydes or ketones ([C.sub.25]-[C.sub.29]), and more complex ring-containing structures. ¹H and [sup.13]C nuclear magnetic resonance spectroscopy, and the carbon/hydrogen ratio as determined by microanalysis, confirmed the predominantly aliphatic character of the extracts. Both wettable and water repellent samples contained hydrophobic compounds. The 3 water repellent samples contained far more organic material, although the amount extracted was not related to the degree of water repellency. Perhaps more importantly, they contained polar compounds of high relative molecular mass, which were almost absent from the wettable subsoil. It may be speculated that these are the compounds in this soil whose presence in significant amounts is necessary for water repellency to be exhibited. Additional keywords: hydrophobicity, gas chromatography., Introduction It is widely accepted that soil water repellency is caused by hydrophobic organic compounds deposited on soil mineral or aggregate surfaces or present as interstitial matter (Wallis and Home [...]

After an initial evaluation of several solvents, the efficiency of Soxhlet extractions with isopropanol/ammonia (s.g. 0.88) (70:30 v:v; 24 h) in extracting compounds associated with water repellency in sandy soils was examined using a range of repellent and wettable control soils (n = 15 and 4) from Australia, Greece, Portugal, The Netherlands, and the UK. Extraction efficiency and the role of the extracts in causing soil water repellency was examined by determining extract mass, sample organic carbon content and water repellency (after drying at 20°C and 105°C) pre- and post-extraction, and amounts of aliphatic C-H removed using DRIFT, and by assessing the ability of extracts to cause repellency in acid-washed sand (AWS). Key findings are: (i) none of organic carbon content, amount of aliphatic C-H, or amount of material extracted give any significant correlation with repellency for this diverse range of soils; (ii) sample drying at 105°C is not necessarily useful before extraction, but may provide additional information on extraction effectiveness when used after extraction; (iii) the extraction removed repellency completely from 13 of the 15 repellent samples; (iv) extracts from all repellent and wettable control soils were capable of inducing repellency in AWS. The findings suggest that compounds responsible for repellency represent only a fraction of the extract composition and that their presence does not necessarily always cause repellency. Additional keywords: water repellency, water repellence, hydrophobicity, extraction, aliphatic, DRIFT., Introduction It has been proposed that water repellency is caused by the accumulation of hydrophobic organic compounds released from roots (Dekker and Ritsema 1996; Doerr et al. 1998), as fungal [...]

The effects of variation in heating temperature T (50-300°C), heating duration (20-60 min), and postheating equilibration times (24-168h at 20°C and 50% relative humidity) on the wettability, as measured by the Critical Surface Tension (CST) method, of 4 initially water repellent soils from Canada, Portugal, and the UK are reported. All soils show an increase in water repellency following heating at temperatures in the range of 50 to 150°C, followed by a considerable decline after heating to 200-250°C, and, except for one soil, the eradication of repellency after heating to 300°C. For two soils with a comparatively high organic carbon content and fine texture, water repellency levels were also affected by the length of the post-heating equilibration period. The results demonstrate that (i) the common practice of heating samples to 105°C does not provide a viable standard procedure for the measurement of water repellency as it may alter repellency to different degrees, and (ii) where heat treatment is required, a post-heating equilibration time of 24 h is not necessarily sufficient for sample repellency levels to adjust to atmospheric laboratory conditions; therefore it is advisable to prolong equilibration to at least one week prior to measurement. Additional keywords: hydrophobicity, water repellence, water repellent., Introduction It has long been established that heating of potentially water repellent soils, whether in situ or in the laboratory, can influence their wettability. For example, drying soils at temperatures [...]

Dye-sensitised solar cells were made using variations of a standard procedure, including the introduction of new binder materials into the TiO2 semiconductor films. It was found that the degree of cracking of the films can be influenced by both their thickness and the nature of the binder. Photoelectric measurements of working solar cells were carried out. The changes of influential cell parameters with temperature are reported here, and discussed on the basis of the electrical cell equations. [ABSTRACT FROM AUTHOR]

Schizophrenia is a common psychiatric disorder with a complex genetic etiology. To understand the genetic basis of this syndrome in Portuguese Island populations, we performed a genome-wide scan of 29 families with schizophrenia, which identified a single region on 5q31-5q35 with strong linkage (NPL=3.09, P=0.0012 at D5S820). Empirical simulations set a genome-wide threshold of NPL=3.10 for significant linkage. Additional support for this locus in schizophrenia comes from higher-density mapping and mapping of 11 additional families. The combined set of 40 families had a peak NPL=3.28 (P=0.00066) at markers D5S2112-D5S820. These data and previous linkage findings from other investigators provide strong and consistent evidence for this genomic region as a susceptibility locus for schizophrenia. Exploratory analyses of a novel phenotype, psychosis, in families with schizophrenia and bipolar disorder detected evidence for linkage to the same markers as found in schizophrenia (peak NPL=3.03, P=0.0012 at D5S820), suggesting that this locus may be responsible for the psychotic symptoms observed in both diseases.Molecular Psychiatry (2004) 9, 213-218. doi:10.1038/sj.mp.4001418 Published online 30 December 2003 [ABSTRACT FROM AUTHOR]