Surface Liquid Contaminations

Contaminants include not only foreign bodies but also liquids or slurries that may be splashed onto the food products and create spots. For example, fecal contamination has caused food-borne diseases due to Escherichia coli, which in turn led to a thorough inveshgation of both apples and poultry. The first investigahons into hyperspectral imaging as applied to fecal contaminahon were started at the U S DA/ 

ARS Beltsville research center by Y.-R. Chen, R. Lu and B. Park [22], and later still by the teams of both Park and Lawrence at USDA Athens/GA, while Beltsville focused more on surface contaminants on apples. 

Poultry provides another, much more complex, example of litter-contaminated food product. The complexity is generated both by the odd shape of poultry carcasses, with several concave shaded areas (under the wings and the leg folds), by the heterogeneity of the skin color due to the relative transparency of the chicken skin, and by the various causes of safety hazards in chicken here, not only litter contamination must be detected, but also cadaver, septicemia and tumor problems among others. 

In Beltsville, several studies followed in quick succession, each based on the ISL hyperspectral imager with the aim of differentiating wholesome carcasses from cadaver, septicemia and tumor carcasses. In a preliminary study [22], the system was calibrated spectrally and tested on four classes of chicken carcass to determine the best discriminating spectral ranges for this, 650-900nm was selected based on qualitative observations. In a later study [25], a dual-wavelength camera was developed and tested. 

The Athens hyperspectral system was similar to that produced by the Beltsville group, being composed of an Imspector PGP spectrograph and a CCD camera. 

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Surface liquid is probably the most common form of PCB contamination, since spills are the most common PCB-related incident. Surface liquid contamination can result from spills that are immediately cleaned up or from tracking of PCB by firemen or others... 

All rated fireproofing systems should be carefully installed to specification and manufacturer s requirements. Substrate surfaces should be cleaned so they are free from oil, grease, liquid contaminants, rust, scale, and dust. If a primer is required, it should be compatible with the fireproofing. Specifications to be followed include the specified thickness or number of layers, adequate attachment, and proper caulking, sealing, or top-coating of the systems. 

The generalized graphical correlation presented in Fig. 2.5 gives one method of estimating terminal velocities of drops and bubbles in infinite liquid media. For more accurate predictions, it is useful to have terminal velocities correlated explicitly in terms of system variables. To obtain such a correlation is especially difficult for the ellipsoidal regime where surface-active contaminants are important and where secondary motion can be marked. 

This experiment requires skill and careful technique in order to obtain accurate results. As with most surface chemistry experiments cleanliness is of paramount importance. High-energy liquids such as water easily pick up surface-active contaminants from the air in a laboratory and great care should be taken to reduce exposure. Contaminants generally do not adsorb at the surface of low-energy liquids such as hexane and hence are less of a problem. 

Other advantages of using mercury (or any other liquid metal) as an electrode are prevention of surface contaminants and surface reproducibility. If a mercuiy-drop electrode is used, eveiy time a drop falls and a new drop forms, the electrode presents a virgin surface to the solution. With a simple capillary connected to a reservoir, contamination problems are circumvented. Also, the use of liquid metals removes complications from the characteristic structure and topography present in solid surfaces. Liquid surfaces are nonstructured and highly reproducible. 

Because of the availability of these new methods, devices, and purer materials, it has become more feasible to carry on effective research with adequate surface-chemical control of gas and liquid adsorption, wetting, adhesion, emulsification, foaming, boundary friction, corrosion inhibition, heterogeneous catalysis, electrophoresis, electrode surface potentials, and a variety of other subjects of interest in the surface-chemical and allied fields of research. In view of the present situation, serious investigators should now be able to report results in the scientific literature which will have much more value than ever before. There is no excuse for any investigator s taking such inadequate care in controlling surface composition or surface-active contaminants as was common in over 50% of the research publications in surface and colloid science in the past. 

Removal of solid-phase surface radioactive contamination with no liquid radioactive waste generation... 

The settling time in this work appears to be a measure of the surface-active contamination present in the particular system being studied. Vermeulen et al. also noted considerable variability in their results which they ascribed to surface-active agents. Neither they nor Rodger et al. were able to observe changes in interfacial surface tension to account for the apparent changes in interface contamination. It would appear that equilibrium drop size in liquid-liquid systems is sensitive to remarkably small amounts of interface contaminations. 

The autoignition temperature (AIT) or tlte maximum spontaneous ignition temperature is defined as the maximum temperature at which combustion occurs in a combustible bulk gas mixture when tlie temperature of a flammable gas-air mixture is raised in a uniformly heated apparatus. The AIT represents a tlircshold below which chemicals and combustibles can be handled s ely. (The AlTs of selected substances arc available in the literature. ) The AIT is strongly independent on tlie nature of hot surfaces. The AIT may be reduced by as mudi as 100-200°C when the surfaces arc contaminated by dust. When tlie temperature of a flanuiiable mi.xturc is raised to or above the autoignition temperature, ignition is not spontaneous. Most notably in liquids, there is a finite delay before ignition lakes place, i.e., a lapse between the time tlicrc is a flammable mixture reaches its flame temperature and tlie first appearance of a flame. An equation tliat correlates with the ignition temperature is also available in the literature. ... 

The curves for the drag coefficient and the terminal velocity converge for small and large bubbles. This is likely to be because there is always some surface active contaminants present, even in distilled water, that will prevent the internal circulation of the smallest bubbles. For the large bubbles the surface tension forces are not important. Several different drag formulations are given based on the Reynolds number and the density ratio of the gas and liquid [54, 163, 78]. 

The purity of solvents, especially in studies at liquid-liquid interfaces, is as important as the purity of the surfactant sample. The proven absence of any surface active contamination, both in the surfactant sample and in the solvents, is a necessary prerequisite for interfacial studies. The picture shown in Fig. 5.6 demonstrates the situation. 

This anomalous wetting behavior of the low surface tension liquids on additive-free PAM may indicate that the polymer surface is contaminated. The most probable contaminant on the surface of this water-soluble polymer would be a layer of strongly adsorbed water, which is... 

Various known factors affecting cavitation in conventional-scale systems are altered in microscale systems, such as flow dimensionless parameters, component geometries, liquid contaminants (nuclei sources), and surface roughness and chemistry (surface energy). The differences arise from various causes including microfabrication constraints, typical choice of device materials, and the Reynolds number. Subsequent sections will discuss each effect in detail. 

As compared to non-adsorbent fabrics that could also be used to remove hazardous liquids contaminants from solid surfaces, the adsorptive properties of the activated carbon fabrics mitigates off-gassing from used wipes. When the used wipes are repackaged in a sealable hermetic envelope, the adsorptive properties provide a redimdant means of agent isolation. The used wipes can thus be safely handled imtil they are destroyed, for example, by incineration, or decontaminated by standard means, such as immersion in bleach solution. 

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