Vacuum embedding

Vacuum embedding can be carried out to remove air bubbles from the tissue and rapidly replace the clearing agent with paraffin. This approach is especially desirable for air-containing tissues such as lung or hard tissues such as fibrous or scar tissues. The vacuum should not exceed 400-500 mm of mercury to avoid damage to the tissue. 

The surface properties of these nano-objects match those of metal nano crystals prepared in ultrahigh vacuum, for example the C - O stretch of adsorbed carbon monoxide or the magnetic properties of cobalt particles embedded in PVP. This demonstrates the clean character of the surface of these particles and its availabihty for reactivity studies. 

In 1995, one of the authors (A.K.) introduced the state of a molecule embedded in a perfect conductor as an alternative reference state, which is almost as clean and simple as the vacuum state. In this state the conductor screens all long-range Coulomb interactions by polarization charges on the molecular interaction surface. Thus, we have a different reference state of noninteracting molecules. This state may be considered as the North Pole of our globe. Due to its computational accessibility by quantum chemical calculations combined with the conductor-like screening model (COSMO) [21] we will denote this as the COSMO state. 

Bacterial spores have been deliberately taken into space, in particular spores of the bacterium Bacillus subtilis. Up to 70 per cent of the bacterial spores survive in the short term for approximately 10 days of exposure to space vacuum. The chances of survival in space are increased if the spores are embedded in chemical protection such as sugars, or salt crystals, or if they are exposed in thick layers. For example, 30 per cent of B. subtilis spores survived for nearly 6 years in space when embedded in salt crystals and 80 per cent survived in the presence of glucose. Bacillus subtilis spores in Dominican amber have remained viable for several million years. Transport to a friendly environment with a source of energy is all that is required for life to be seeded on this planet or the next. 

Zsolnay and Kiel [26] have used flow calorimetry to determine total hydrocarbons in seawater. In this method the seawater (1 litre) was extracted with trichlorotrifluoroethane (10 ml) and the extract was concentrated, first in a vacuum desiccator, then with a stream of nitrogen to 10 pi A 50 pi portion of this solution was injected into a stainless steel column (5 cm x 1.8 mm) packed with silica gel (0.063-0.2 mm) deactivated with 10% of water. Elution was effected, under pressure of helium, with trichlorotrifluoroethane at 5.2 ml per hour and the eluate passed through the calorimeter. In this the solution flowed over a reference thermistor and thence over a detector thermistor. The latter was embedded in porous glass beads on which the solutes were adsorbed with evolution of heat. The difference in temperature between the two thermistors was recorded. The area of the desorption peak was proportional to the amount of solute present. 

All of the samples analyzed were standard one-inch diameter polished thin sections. Whenever feasible the samples received a final, cleansing polish with 1 pm diamond compound made from commercial graded diamonds embedded in "vaseline". Commercial diamond paste has proved unsatisfactory due to high levels of K, Na, Cl, Si, F, and Ca. Samples are then cleaned with carbon tetrachloride, rinsed in ethanol, and coated with vacuum evaporator. This sample preparation technique was developed during our studies of minor elements [16,17] and has proved to produce consistently contamination-free samples. 

Figure 2 shows STEM images of a 8%wt Pd/2%wt Pt catalyst which is supported on charcoal. The sample was prepared for microscopy by embedding in epoxy resin and sectioning with a diamond knife in an ultramicrotome, and was examined in a Vacuum Generator s Ltd HB5 STEM, with a 5A probe. The sample thickness is about 500A. 

Si spheres embedded in a vacuum with 45% nominal porosity [Kol5], micro PS shows a significantly lower absorption in the visible than expected from a calculation for 72% nominal porosity. After [Ko4]. 

Let us now consider extinction by a single arbitrary particle embedded in a nonabsorbing medium (not necessarily a vacuum) and illuminated by a plane wave (Fig. 3.7). We construct an imaginary sphere of radius r around the particle the net rate at which electromagnetic energy crosses the surface A of this sphere is... 

If the charges are embedded in a medium, the electrical properties of the intervening molecules decrease the force from the value calculated by Equation (4). The relative dielectric constant of the medium er measures this effect quantitatively. In surroundings other than a vacuum, the force between two charges is given by... 

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