Bubble trapping

Carbon dioxide, considered a wanning gas, comprises about 0.036 percent of the atmosphere by volume. As Figure 1 shows, carbon dioxide levels have increased as a component of the atmosphere by nearly 30 percent from the late eighteenth century to the end of the twentieth century, when the level was close to 365 parts per million by volume. Prior to the period of industrialization, carbon dioxide levels were largely stable, at about 280 parts per million, though fluctuations as low as 200 parts per million or as high as 300 parts per million have been observed through analysis of air bubbles trapped in arctic ice cores. 

Fig. 11-5 CO2 content of air bubbles trapped in glacial ice from Greenland and Antarctica, showing a pre-industrial concentration of ca. 280 ppmv.

Measurements of CO2 concentrations in air bubbles trapped in glacial ice (Berner et ah, 1980 Delmas et ah, 1980 Jouzel et ah, 1993 Raynaud et ah, 1993) show that atmospheric Pqo was about 200 ppmv toward the end of the last glaciation 20000 years ago (Fig. 11-19). 

A foam is a colloidal dispersion of gas bubbles trapped in a liquid. To produce a stable foam, several characteristics of the liquid are necessary. For example, a viscous liquid facilitates the trapping of gas bubbles. The presence of a surface active agent or stabilizer that, for structural reasons, preferentially locates on the surface of the gas bubble also provides a more permanent foam. A low vapor pressure for the liquid reduces the likelihood that the liquid molecules (particularly those surrounding the bubble) will easily evaporate, thus leading to the collapse of the foam. 

Air bubbles are the nasties in HPLC work. They cause the same type of troubles as with wet-column chromatography, and you just don t want them. So there s usually a bubble trap (Fig. 112) before the eluent reaches the pump. This device is quite simple, really. Bubbles in the eluent stream rise... 

Transfer the animal to the larger coverslip (24 x 60 mm), and pipet away the PBS. Add one drop of monnting medium. Lower the smaller coverslip (22 mm ) onto the animal. Use forceps first to pnt one side of the coverslip into the mounting medium and then to lower the coverslip slowly allowing any air bubbles to be pushed to the edge. Avoid dropping the coverslip onto the animal since there will surely be many air bubbles trapped beneath it (see Note 11). 

Many of these questions are not purely academic. For example, it is well known that ice bubbles trapped in ice sheets such as the one covering Greenland and Antarctica can be used to reconstruct the composition of earth s atmosphere over the past 750,000 years... 

Figuro 2-8 An air bubble trapped beneath the stopcock should be expelled before you use the buret...

How do scientists estimate the age of ancient air in bubbles trapped in an ice core ... 

Samples are usually placed in 1mm thick quartz spectrophotometer cells sealed with Parafilm or similar. Samples in which the aqueous phase has a very high D to H ratio are sometimes thicker, as the level of incoherent scatter due to H will be low. Samples may be in the scattering apparatus for several hours, and so H20/D20 exchange due to faulty sealing can cause errors. For gel-like samples, it is very important that there are no air bubbles trapped in the sample. Gel or viscous samples can be centrifuged to the bottom of cells, and air bubbles removed, using a Helma Roto-Vette or similar. 

Similarly, some solid foams (e.g. foam rubber) consist of spherical gas bubbles trapped within a solid network, whereas others (e.g. expanded polystyrene) consist of as little as 1 per cent solid volume and are composed of polyhedral gas cells separated by very thin solid walls. 

To imprint more complex structures, a Si master with positive relief structures was first created. Then the master was used to imprint the channel pattern on a PMMA plate (135°C for 5 min) (see Figure 2.22) [1011]. This method is called compression molding or embossing. In using this method, a vacuum chamber is needed to remove air bubbles trapped at small features and to remove water vapor from the polymer [7]. 

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