Two-filter method

The instruments include an ionization chamber, the charcoal-trap technique, a flow-type ionization chamber (pulse-counting technique), a two-filter method, an electrostatic collection method and a passive integrating radon monitor. All instruments except for the passive radon monitor have been calibrated independently. Measurements were performed... 

Two-Filter Method TF flow rate 40 /min, sampling time lhr, filter membrane filter, gross counting or -spectrometry, Rn and Tn measured... 

Two-Filter Method (TF). The Two Filter Method was first introduced by Thomas and LeClare (Thomas and LeClare, 1970). A modified 66.3 liter decay chamber was used with a filter on each end. Air was sampled at 40 /min. The inlet filter removed all of the radon daughters and aerosol particles but allowed radon gas to pass. 

Thomas, J.W. LeClare, P. (1970) A study of the two filter method for radon-222. Health Physics, 18, 113-22. 

Two-filter methods This method consists of a two-filter tube with a scintillation phototube detector placed in front of the exit filter. The air is drawn continuously through the tube. The first filter removes all the radon decay products from the sampled air. This air is then passed through a long decay tube, where daughter products are allowed to develop and are collected on a second filter, the activity of which is proportional to the radon concentration in the sampled air. 

Open air two filter method (parallel plate) 0.03 Duggan and Howell (1969)... 

In outdoor air, Duggan and Howell (1969), using the two filter method, found the unattached fraction to contain about 3% of the ambient radioactivity. Raghavayya and Jones (1974), using the wire screen method (screens of 120 mesh/inch), found / to range from 4.0 to 33.2%, with a median value of 5.2%. The ICRP (1981) recommends a value of between 0.00 and 0.05 for the unattached fraction in most occupational exposure conditions. 

The experimental conditions used to determine the CFPP do not exactly reflect those observed in vehicles the differences are due to the spaces in the filter mesh which are much larger in the laboratory filter, the back-pressure and the cooling rate. Also, research is continuing on procedures that are more representative of the actual behavior of diesel fuel in a vehicle and which correlate better with the temperature said to be operability , the threshold value for the Incident. In 1993, the CEN looked at two new methods, one called SFPP proposed by Exxon Chemicals (David et al., 1993), the other called AGELFI and recommended by Agip, Elf and Fina (Hamon et al., 1993). 

McCormack D A, Kroes G J and Neuhauser D 1998 Resonance affected scattering Comparison of two hybrid methods involving filter diagonalization and the Lanczos method J. Chem. Phys. 109 5177... 

Pour typical weU patterns for contaminant plume containment are described in Ref. 16. The first is a pair of injection-production weUs. The second is a line of downgradient pumping weUs. The third is a pattern of injection-production weUs around the boundary of a plume. The fourth, the double-cell system, uses an inner ceU and outer recirculation ceU, with four ceUs along a line bisecting the plume in the direction of flow. Two other methods of plume containment are bio filters and a fuimel-and-gate system, which are described in the in bioremediation section. 

The collection technique involves the removal of particles from the air stream. The two principal methods are filtration and impaction. Filtrahon consists of collecting particles on a filter surface by three processes—direct interception, inertial impaction, and diffusion (5). Filtration attempts to remove a very high percentage of the mass and number of particles by these three processes. Any size classification is done by a preclassifier, such as an impactor, before the particle stream reaches the surface of the filter. 

A more flexible option from an operational viewpoint is the implementation of process-oriented enhancements that intensify particle separation. This can be achieved by two different methods. In the first method, the suspension to be separated is pretreated to obtain a cake with minimal resistance. This involves the addition of filter aids, flocculants or electrolytes to the suspension. In the second method, the period during which suspensions are formed provides the opportunity to alter suspension properties or conditions that are more favorable to... 

The filtered product is then thoroughly washed with water and crystallized from a benz or acet soln. For details see Ref 82, pp 59—61 An alternate, two-stage method of producing Tetryl is used in Germany. In the first stage dinitrome thy laniline is prepd by reacting chloro-dinitrobenzene with methylamine in the presence of Na hydroxide. In the second stage the... 

Organic solvent extraction. Two analytical methods for acetamiprid have been developed One method is for the parent only and the other determines the total residue of the parent and its metabolites (lM-1-2, lM-1-4 and lC-0). Air-dried soil (20-g equivalent dry soil) is weighed into a centrifuge tube and imidacloprid residue is extracted with 100 mL of methanol-0.1M ammonium chloride (4 1, v/v) using a mechanical shaker for about 30 min. After shaking, the tube is centrifuged at 8000 rpm for 2 min. The supernatant is filtered and the analysis of the soil residue is carried out in the same manner as described above for the parent compound. 

In a solubility experiment the solubility of the compound of interest is measured in the presence and absence of dissolved humic materials. Two techniques were used to measure solubility a shake and filter method similar to that used by Yalkowsky, and a flow through column technique similar to that used by May et al. 9 The measured solubilities of a number of compounds in our experiments were always higher in the presence of humic materials. This increase in the solubility is due to the binding of the compound by humic materials. In the presence of humic materials the measured solubility consists of two fractions free and bound. The free concentration should be the same in the presence or absence of humic materials. The difference between the solubilities of the compound in the presence and absence of humic materials is therefore a measurement of the bound fraction. 

If the two symmetric coherence transfer pathways are designed to have the same efficiency and thus yield signals with the same amplitude (e.g., by using the popular z-filter method (Fig. 12a) [168]), the resulting signal can be written as... 

In the adsorption with Tenax alone satisfactory results were obtained, while in the presence of mineral oil a considerable proportion of the organophos-phorus pesticides (particularly Malathion and Parathion-methyl) was not adsorbed and was recovered in the filtered water. This drawback can be overcome by adding a layer of Celite 545 which, in order to prevent blocking of the column, is mixed with silanised glass wool plugs. A number of analyses of surface and estuarine sea waters were carried out by this modified Tenax column and simultaneously by the liquid-liquid extraction technique. To some of the samples taken, standard mixtures of pesticides were also added, each at the level of 1 xg/l (i.e., in concentration from 13 to 500 times higher than that usually found in the waters analysed). One recovery trial also specifically concerned polychlorobiphenyls. The results obtained in these tests show that the two extraction methods, when applied to surface waters that were not filtered before extraction, yielded very similar results for many insecticides, with the exception of compounds of the DDT series, for which discordant results were frequently obtained. 

Resonance Affected Scattering Comparison of Two Hybrid Methods Involving Filter Diagonalization and the Lanczos Method. 

Example 10 Choice among Alternatives Two filters are considered for installation in a process to remove solids from a liquid discharge stream to meet environmental requirements. The equipment is to be depreciated over a 7-year period by the straight-line method. The income tax rate is 35 percent, and 15 percent continuous interest is to be used. Assume that the service life is 7 years and there is no capital recovery. Data for the two systems are as follows ... 

An informal intercomparison of these two CIMS methods with a filter pack method shows generally excellent agreement between the mass spectrometric approaches and often, but not uniformly, good agreement with the filter pack method (Fehsenfeld et al., 1998). The latter was often high, which was attributed to interference from decomposition of ammonium nitrate to HNO-, + NH3 on the Teflon particle prefilter, followed by absorption of the HNO-, by the nylon filter. 

There are two other methods of purification listed in Ref 17, p 146. Steiner dissolved crude MF in coned aq soln of KCN followed by adding coned HC1 and washing the resulting ppt with w. Solonina dissolved 1 part of crude MF in 7 parts of pyridine, filtered the soln and poured it into 100 parts of cold w... 

We have presented two deconvolution methods from an intuitive point of view. The approach that suits the reader s intuition best depends, of course, on the reader s background. For those versed in linear algebra, methods that stem from a basic matrix formulation of the problem may lend particular insight. In this section we demonstrate a matrix approach that can be related to Van Cittert s method. In Section IV.D, both approaches will be shown to be equivalent to Fourier inverse filtering. Similar connections can be made for all linear methods, and many limitations of a given linear method are common to all. 

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