The use of insulated time-domain reflectometry sensors to measure water content in highly saline soils

In a conducting medium, the energy of a time-domain reflectometry (TDR) pulse is dissipated and the signal is attenuated. Above a certain high conductivity, however, the signal is completely attenuated and the soil short-circuits the sensor. This behaviour of the signal with conductivity severely limits the TDR technique in measuring water content in highly saline soils. By reducing the direct contact between the conductive soil and the metallic sensor the energy of the pulse is better maintained. Different combinations were tried: we insulated the central wire, outer two wires, and all wires of a three-wire sensor with two different insulators. The first insulator was an adhesive polyethylene sheet usually used as a transparent cover and the second insulator was an adhesive tape. The insulated sensors were used to measure dielectric constants in non-saline soils and water and in saline soils. The sensors with the insulated centre wire preserve maximum energy and maintain a clear signal in saline soils. The insulating materials have very small dielectric constants. The TDR exerts a larger influence in the vicinity of the wires of the sensor during measurements. Therefore, the insulated sensor measures a dielectric constant which is smaller than the apparent dielectric constant of the surrounding medium. The type of insulating material also has an effect on the dielectric constant. Therefore, it is necessary to calibrate the sensors for the specific insulator. Received: 30 December 1996     

Interaction of tea polyphenols and food constituents with model gut epithelia: the protective role of the mucus gel layer

The luminal surface of the gastrointestinal tract is covered by a mucus gel layer that acts to protect gut epithelial cells from the harsh luminal environment. This study investigated the use of two human colonic adenocarcinoma cell lines, HT29-MTX-E12 and HT29, as a model to mimic gut epithelium with and without a mucus gel layer. The effect of adding the tea polyphenols epigallocatechin gallate (EGCG) and epicatechin (EC) to the cells with subsequent examination of cell morphology and viability was assessed. EGCG, at the concentrations tested, was very toxic to the HT29 cells, but less toxic to the HT29-MTX-E12 cells, suggesting that the mucus gel layer on the HT29-MTX-E12 cells can protect the cells against EGCG toxicity. In contrast, EC had no effect on the viability of either the HT29 or HT29-MTX-E12 cells, suggesting that proteins within the mucus gel layer on the apical surface of gut epithelial cells may bind to the galloyl ring of EGCG. The effect of adding food-related ingredients with the ability to complex with EGCG, β-casein and maltodextrin, on cell viability was also examined. The presence of β-casein was very effective in protecting the cells against the toxicity effect of EGCG, but maltodextrin, at the concentration tested, was less effective in protecting against this toxicity. In conclusion, the results demonstrate that the mucus gel layer on HT29 human colonic adenocarcinoma cells may protect these cells against EGCG toxicity. In addition, the data showing reduced toxicity of EC compared to that of EGCG suggest that the cytotoxic effects of high polyphenol levels may be associated with the ability of polyphenols to interact with cellular proteins and mucins.     

Honey with high levels of antioxidants can provide protection to healthy human subjects

Free radicals and reactive oxygen species (ROS) have been implicated in contributing to the processes of aging and disease. Humans protect themselves from these damaging compounds, in part, by absorbing antioxidants from high-antioxidant foods. This report describes the effects of consuming 1.5 g/kg body weight of corn syrup or buckwheat honey on the antioxidant and reducing capacities of plasma in healthy human adults. The corn syrup treatment contained 0.21 +/- 0.06 mg of phenolic antioxidants per gram, and the two buckwheat honey treatments contained 0.79 +/- 0.02 and 1.71 +/- 0.21 mg of phenolic antioxidants per gram. Following consumption of the two honey treatments, plasma total-phenolic content increased (P < 0.05) as did plasma antioxidant and reducing capacities (P < 0.05). These data support the concept that phenolic antioxidants from processed honey are bioavailable, and that they increase antioxidant activity of plasma. It can be speculated that these compounds may augment defenses against oxidative stress and that they might be able to protect humans from oxidative stress. Given that the average sweetener intake by humans is estimated to be in excess of 70 kg per year, the substitution of honey in some foods for traditional sweeteners could result in an enhanced antioxidant defense system in healthy adults.     

Reaction-driven restructuring of Rh-Pd and Pt-Pd core-shell nanoparticles

Heterogeneous catalysts that contain bimetallic nanoparticles may undergo segregation of the metals, driven by oxidizing and reducing environments. The structure and composition of core-shell Rh(0.5)Pd(0.5) and Pt(0.5)Pd(0.5) nanoparticle catalysts were studied in situ, during oxidizing, reducing, and catalytic reactions involving NO, O2, CO, and H2 by x-ray photoelectron spectroscopy at near-ambient pressure. The Rh(0.5)Pd(0.5) nanoparticles underwent dramatic and reversible changes in composition and chemical state in response to oxidizing or reducing conditions. In contrast, no substantial segregation of Pd or Pt atoms was found in Pt(0.5)Pd(0.5) nanoparticles. The different behaviors in restructuring and chemical response of Rh(0.5)Pd(0.5) and Pt(0.5)Pd(0.5) nanoparticle catalysts under the same reaction conditions illustrates the flexibility and tunability of the structure of bimetallic nanoparticle catalysts during catalytic reactions.     

Shellfish aquaculture in Thailand

Abstract

Shellfish have been farmed in Thailand for over 100 years, and during this time, traditional culture techniques have gradually given way to more sophisticated and capital intensive methods. Farmed shellfish production increased from 73,976 to 138,202 metric tonnes between 1988 and 2000. Major species currently under cultivation include the green mussel Perna viridis, the blood cockle Anadara granosa, and three species of oyster (Saccostrea cucullata, Crassostrea belcheri, and Crassostrea iredalei). The horse mussel Arcuatula arcuatula is also produced in limited amounts for animal feed, and gastropods such as the abalone Haliotis asinina and the spotted babylon Babylonia areolata are in the initial phases of commercialization. With the globalization of fisheries commodity markets, the Thai shellfish sector is slowly implementing more rigorous management and certification processes. These procedures are required to access European, American and Japanese markets, and would also serve to decrease the risk of gastrointestinal disease for local consumers.     

Ultra low-level airborne (ULLA) sensing of crop canopy reflectance: A case study using a CropCircle™ sensor

Operational airborne and satellite remote sensing in agriculture remains constrained by matching platform availability to suitable daytime weather and illumination conditions, crop development, and availability of ground staff. An ultra low-level aircraft carrying an active NIR/Red CropCircle™ sensor was successfully deployed to record and subsequently map crop vigour via the simple ratio (SR) index over a field of sorghum. Given the logging frequency of ≈20 Hz and the presence of alternate rows of bare soil, the Moiré effect reduced the contrast between crop and bare soil skip-rows. Such effects would not be expected to occur in non-skip-row crops. The ultra low-level airborne (ULLA)-SR map derived from the 20 m transect records compared favorably with the SR map derived from a meter-resolution airborne digital multispectral image that was re-sampled to a similar spatial resolution. This case study, involving a CropCircle™ sensor mounted in a low-level aircraft demonstrates another deployment option for users of this class of sensor. Moreover, an ULLA configuration offers the potential for greater flexibility in scheduling compared to airborne imaging, given it can be flown at any sun-angle, under cloud, at night, and may easily be incorporated into aircraft already conducting low-level operations, for example crop dusting and reconnaissance, over agricultural fields.