Hot foam for weed control-Do alkyl polyglucoside surfactants used as foaming agents affect the mobility of organic contaminants in soil?

Use of alkyl polyglucosides (APGs) as a foaming agent during hot water weed control may influence the environmental fate of organic contaminants in soil. We studied the effects of the APG-based foaming agent NCC Spuma (C8-C10) on leaching of diuron, glyphosate, and polycyclic aromatic hydrocarbons (PAHs) in sand columns. We also examined how APG concentration affected the apparent water solubility and adsorption of the herbicides and of the PAHs acenaphthene, acenaphthylene and fluorene. Application of APGs at the recommended concentration of 0.3% did not significantly affect leaching of any of the compounds studied. However, at a concentration of 1.5%, leaching of both diuron and glyphosate was significantly increased. The increased leaching corresponded to an increase in apparent water solubility of diuron and a decrease in glyphosate adsorption to the sand. However, APG addition did not significantly affect the mobility of PAHs even though their apparent water solubility was increased. These results suggest that application of APG-based foam during hot water weed control does not significantly affect the mobility of organic contaminants in soil if used according to recommendations. Moreover, they suggest that APGs could be useful for soil bioremediation purposes if higher concentrations are used.

Degradation and leaching of fluroxypyr after application to railway tracks

Fluroxypyr is an auxin-type herbicide used for postemergent control of broad-leaved weeds in agriculture and in nonagricultural environments such as railways. The overall aim of this study was to assess the potential environmental impact from fluroxypyr application to railway tracks and to elucidate some of the factors that control its environmental fate. In laboratory studies, we examined the degradation of fluroxypyr and the formation of its metabolites fluroxypyr-methoxypyridine (F-MP) and fluroxypyr-pyridinol (F-P) in soil from two Swedish railways. We also investigated the degradation and leaching of fluroxypyr in three different railway plots treated with fluroxypyr (360 g ae ha). The half-life of fluroxypyr in soil samples ranged between 28 and 78 d. An estimated mean 48.6 ± 20% of the fluroxypyr was converted into F-P and 8.0 ± 2% into F-MP. The main metabolite, F-P, was rapidly degraded, with an average half-life of 10 ± 5 d. However, F-MP was not degraded to a significant degree in any sample, resulting in slowly increasing concentrations throughout the experiment. This pattern of relatively rapid degradation of F-P and slow accumulation of F-MP was also observed in the field. The persistent nature of F-MP may be of concern if fluroxypyr is used repeatedly at the same location. Fluroxypyr was detected in the groundwater beneath the track at all three locations studied in concentrations exceeding the EU limit of 0.1 μg L for pesticides in drinking water, and F-P was detected in the groundwater at two of three locations. The most important factor controlling fluroxypyr degradation rate in soil was the soil water content, which modulated microbial activity and presumably also fluroxypyr availability to microorganisms. Our findings imply that fluroxypyr may not be a suitable herbicide for weed control on railway tracks.

Perceived structure from optic flow: consistent versus variable mapping of 3-D Euclidean structure

In an earlier study (Börjesson & Lind, 1996), the perception of Euclidean structure from polar projected two-frame apparent motion sequences was studied. The results showed that Euclidean structure is not perceived. However, at larger visual angles a certain consistency in the mapping between distal and perceived structure exists. The aim of the present study was to more precisely examine how this degree of consistency varies as a function of visual angle. In Experiments 1 and 2, slant judgments of simulated and real planes indicated that the degree of consistency is a positive function of visual angle. No definite sign of a Euclidean mapping could, however, be found even in the full view condition. Experiment 3 examined texture gradients and the response method used. The results showed that texture gradients did not influence the degree of consistency of the mapping between distal and judged depth and that the response method was both reliable and valid. However, texture gradients did influence the absolute values of the slant judgments. The role of Euclidean and affine mappings of distal structure is discussed and it is proposed that the perceptually important distinction is not between affine and Euclidean mapping, but rather between two types of affine mappings--consistent and variable.

New methods for determination of glyphosate and (aminomethyl)phosphonic acid in water and soil

New methods were developed to determine glyphosate, N-(phosphonomethyl)glycine, and its major metabolite, (aminomethyl)phosphonic acid in groundwater and soil. The methods involve ligand-exchange, anion-exchange and derivatisation and final identification and quantification by GC-MS. The limits of quantification in this experiment were 0.1 microg l(-1) for both compounds in water and 0.006 microg g(-1) for both compounds in soil. Decomposition in soil and occurrence in groundwater of the herbicide glyphosate was studied after its application for weed control on a Swedish railway embankment.

Perceptual depth synthesis in the visual system as revealed by selective adaptation

Selective adaptations was used to determine the degree of interactions between channels processing relative depth from stereopsis, motion parallax, and texture. Monocular adaptations with motion parallax or binocular stationary adaptation caused test surfaces, viewed either stationary binocularly or monocularly with motion parallax, to appear to slant in the opposite direction compared with the slant initially adapted to. Monocular adaptations on frontoparallel surfaces covered with a pattern of texture gradients caused a subsequently viewed test surface, viewed either monocularly with motion parallax or stationary binocularly, to appear to slant in the opposite direction as the slant indicated by the texture in the adaptation condition. No aftereffect emerged in the monocular stationary test condition. A mechanism of independent channels for relative depth perception is dismissed in favor of a view of an asymmetrical interactive processing of different information sources. The results suggest asymmetrical inhibitory interactions among habituating slant detector units receiving inputs from static disparity, dynamic disparity, and texture gradients.

New method for determination of fecal sterols in urine using non-chlorinated solvents

A new method has been developed to determine a number of sterols in urine using non-chlorinated solvents, namely methyl tert.-butyl ether and methanol (the MTB method). The method involves liquid-liquid extraction, saponification, reextraction, silylation and final identification and quantification by GC-FID. The sterols determined were coprostanol, epicoprostanol, cholesterol and dihydrocholesterol. 5Alpha-cholestane was used as internal standard. The limit of detection for the sterols in this experiment was 2 microg l(-1) urine. Recovery of coprostanol over the range 5-100 microg l(-1) urine by this method was between 80 and 92%.

Visual reinforcement audiometry. Comparison of loudspeaker arrangements

Two different loudspeaker arrangements are currently used when performing Visual Reinforcement Audiometry (VRA). In the one arrangement, the loudspeakers are mounted on separate movable arms and positioned 15 cm from each ear. In the other, the loudspeakers are rigidly mounted close to their respective picture monitor at a distance of 50-70 cm from the child. In the present study, these two arrangements were compared by measuring real-ear sound pressure levels and actual sound field conditions. It was shown that a predominantly monaural stimulation was best achieved by using the 15-cm position, but also that the measurements were significantly more affected by small head movements when using this close position. When assessing the acoustics as well as practical aspects, it was concluded that loudspeakers mounted beside the picture monitors at a distance of 50-70 cm from the child makes a generally appropriate arrangement for VRA.

The effect of polar projection on the perception of euclidean structure from motion

The aim of the present study was to examine whether euclidean structure could be recovered from apparent motion sequences under polar projection. In Experiment 1, length judgments of two sides of a simulated triangle rotating in depth did not reveal effects of type of projection, polar or parallel, on the perception of euclidean structure. However, there was a significant correlation between simulated and produced slants. The results also indicated that absolute depth judgments could not be accounted for by a random mechanism suggested by Todd and Bressan (1990). Experiments 2 and 3, in which a continuous dot surface was substituted for the triangle, showed that polar projection information from a relatively large visual angle, 17.40 degrees, as compared with a small visual angle, 4.35 degrees, facilitated discrimination of depth. Produced height:width ratios were consistently related to simulated shape, although the depth dimension was underestimated. Finally, Experiment 4 showed significant correlations between simulated and produced height:width ratios that could be accounted for only by an analysis in which X and Y velocities were treated independently. As in previous experiments, the variation in the depth dimension was underestimated. It was concluded that the visual system utilizes the additional information that is available in polar projection when recovering structure from motion, but that for different reasons the perceived structure does not become euclidean. These reasons are discussed briefly.

Segregation of motion structure from random visual noise

A potential source of information about spatial layout, surface slant, and self-motion is provided by transformations of the optic flow field. Theoretical analyses have demonstrated that such flow fields can be decomposed into translation, rotation, expansion, and deformation components. The objective in this study was to investigate the effectiveness of these motions as visual primitives for preattentive scene segregation. The stimuli consisted of two-frame patterns containing 998 dots. A variable number of these dots (5 to 50) were defined as target dots, representing a specific motion structure, with the residual dots defined as a noise field. The observers' task was to identify the location and type of motion structure. On the basis of the number of target dots needed to detect and correctly identify the target structure, it was determined that translation was the most easily detected structure, followed by rotation, expansion, and compression. Deformation was found to have a detection threshold as high as compression. The results are related to other studies of these motion components.

Motion structure in five-dot patterns as a determinant of perceptual grouping

The effect of basic motion structures on perceptual grouping was studied with five-dot motion patterns. Four basic motion structures were identified in terms of proximal common and relative motion vectors. In a forced-choice situation, the observers had to decide to which of two pairs of dots a fifth critical dot seemed to belong. Thus, one of two possible three-dot units was chosen by the observers. The two possible three-dot units defined different motion structures, and the chosen motion structure was considered to have stronger grouping power than the alternative structure had. It was found that parallel common motions (perceived translation in the plane) had the strongest grouping power; these were followed by circular common motions (perceived rotation in the plane), concurrent relative motions (perceived translation in depth), and, finally, parallel relative motions (perceived rotation in depth). The results also suggested effects of proximity and orientation of axis of rotation. It is further argued that the relative grouping power of the motion structures could not solely be interpreted in terms of changes of directions and distances between the dots. Instead it is suggested that vector analysis is a fundamental perceptual activity and that basic motion structures determine grouping power.