Drying experimental methods

Experimentally, the BBB disruption can be assessed by the administration of dyes (e.g., Evans blue, Fluorescein) or radioactive tracers (e.g., [14C] sucrose) and visualization or measurement of their distribution in the brain parenchyma on tissue sections (Fig. 8.1). To estimate brain water content, the weight of a brain is determined with the wet-and-dry-weight method , i.e., weighing the tissue speci-... 

There is no simple device which enables the measurement of dry deposition in a manner as convenient as for wet deposition. Instead, comparatively less direct methods must be used, none of which is fully proven as yet. For particle exchange, leaf-washing and through-fall techniques (1) can provide measurements of the accumulated deposit on natural surfaces. Likewise, accumulation on snow surfaces can be sampled, and subjected to subsequent chemical analysis. It is evident, however, that such methods only apply in certain circumstances. Budget techniques are sometimes advocated, such as in the case of calibrated watersheds, but these have rarely delivered unequivocal results. The difficulty that arises is that the dry deposition must necessarily be computed as the difference between poorly determined in-flow and out-flow measurements. These, and. a wide variety of other experimental methods, have been reviewed elsewhere (2). 

Figure 4. Comparison of M from the viscometer to M from the DRI detector. Open squares were obtained using the Mp values supplied with the standards (concentration detector MpJ in calibration. Filled squares are obtained when viscometer Mp values determined by the experimental method detailed in the text are used in calibration.

Two different experimental methods were used in this work, one following standard polyacetylene vacuum line/dry box techniques and the other employing a dry box setup only. Both methods gave similar results, although rigorous exclusion of contaminants such as oxygen and water was more difficult to achieve with the all-dry box method. 

Experimental difficulties with the all-dry box method were many. Polymerizations were slow or did not occur at all. Successful experiments occurred only sporadically, and these frustrations led to... 

Experimental Methods. The acid form of the membrane with an equivalent weight (i.e. the weight of polymer per SO3H group) of 1200 was neutralized to about 50 % by immersion of a thin foil (=300 ym) in an aqueous solution of 57-ferric chloride. The setmples were dried in vacuum at room temperature and then hydrated at different humidity levels. For a given humidity level, the quantity of absorbed water is largely dependent on the state of the polymer... 

Models were therefore developed for predicting release from systems of various shapes, and a special hemisphere system [coated everywhere with an impermeable coating except for an aperture in the center face (Fig. 4)] worked best. An experimental method for making the special hemisphere device was then developed to test the predictions. In this procedure the bottoms of test tubes were cut off and used as molds. A low-temperature casting and drying procedure was used. Using this approach, a constant release rate of 0.5 mg/day for 2 months (the duration of the experiment) for test macromolecules (11) was obtained. 

A survey of microwave activation in the chemistry of Hantzsch 1,4-dihydropyridines (1,4-DHP) was reported in 2003 [195]. The experimental method proposed more than a century ago remains the most widely used for synthesis of these heterocycles. Since 1992 the process has been adapted to microwave irradiation under a variety of conditions to reduce the reaction time and enhance the yield. Among these experiments, Zhang reported a solvent-free process starting from 3-aminocrotonate (20 mmol), methyl acetoacetate (20 mmol), and aromatic aldehydes (20 mmol) in a domestic oven [196]. Yields from 59 to 77% were reported for 10-min reaction. A variety of conditions (solution, dry media, solvent-free) has been used for microwave-assisted synthesis of Hantzsch 1,4-DHP. Only procedures involving solvent-free conditions under the action of microwave irradiation led to the aromatized pyridine derivatives. 

Effective diffusivities, reported in the literature, have been usually estimated from drying or sorption rate data. Experimental data are scarce because of the effect of the experimental method, the method of analysis, the variations in composition and structure of the examined materials, and so on. Data of effective diffusion coefficients are available for inorganic materials [20], polymers [8], and foods [21,22]. 

In the previous sections, methods of experimental determination of heat and mass transport properties have been discussed. These methods use special apparatus and are based on the equation of definition of the corresponding property. This section discusses the experimental determination of these properties from drying experiments. Some relevant techniques have been already discussed by Molnar [125]. However, a generalized method based on model-building techniques is presented here. The method uses a drying experimental apparatus and estimates the heat and mass transport properties as parameters of a drying model that incorporates these properties [28,43,177-181]. An outline of the method is described below. 

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