Planar freezing

Whereas lake ice thickens vertically with a planar freezing interface, sea ice grow th is cellular A theoretical treatment of the planar-cellular transition under natural... 

Cellular freezing of natural waters implies a much larger interstitial solute incorporation in form of liquid brine than planar freezing. The planar-cellular transition may therefore be identified as a change to a milky ice appearance or by a sharp increase in the effective solute distribution coefficient Systematic observations of the... 

C. Korber, M.W. Scheiwe and K. Wollhdver, Solute polarization during planar freezing of aqueous salt solutions, Int. J. Heat Mass Trans., 1983, 26, 1241-1253. 

Nunner [ 1.104] photographed with a special cryomicroscope the change of the planar front of a 0.9 ck NaCl solution during directional freezing in 360 s to a stable dendritic ice structure (Fig. 1.37). The concentrated NaCl (dark border) ean be seen on the surface of the ice crystals. 

If the shelf and the tray are as planar as technically possible, the plot marked s = 0 applies. At 0.2 mbar, a heat transfer coefficient of approx. 85 kJ/m2 h °C can be achieved, rising by a factor of two at 1 mbar. In a well designed freeze drying plant with planar trays or vials a heat transfer coefficient of 160 kJ/h m2 °C at 0.9 mbar is possible (Fig. 1.59), while at a pressure of 0.45 mbar, approx. 120 kJ/h m2 °C (Table 1.9) is measured for the heat transfer coefficient A"tot. To sublimate 1 kg of ice per hour and m2 with a coefficient of... 

Petty and Orazio (1996) developed an interesting variation in SPMD liquid phases. The approach consisted of both LDPE and silastic ffibes containing silicone fluid (50 cSt or 3200 MW) with 3% by weight PX-21 activated carbon. The presence of the activated carbon enhanced retention of planar molecules such as PAHs and the silicone fluid remains liquid at temperatures below freezing. However, the partition coefficients of HOCs for this type of silicone fluid are much lower than for triolein. 

With this model, it is necessary to assume fast inversion of the two corannulene units within the dimer (or planarity) otherwise the top and bottom bowls would not be equivalent in the NMR spectra. MNDO calculations predict an activation enthalpy of approximately 13 kcal/mol for the concerted inversion process, and this value is inconsistent with the NMR behavior that shows no evidence of freezing out such a dynamic process. These calculations, however, do not take solvation of the exterior lithiums into account, and so the exterior lithiums were removed, and the system was calculated under conditions that would roughly model solvent separation of the lithium cations. Accordingly, the approximate barrier for inversion was lowered to approximately 1 kcal/mol, suggesting that solvation of the exterior lithium cations can indeed greatly reduce the inversion barrier. ... 

Fig. 7 SEM (magnification 3000) of freeze-dried BC. a CMC-modified (thicker fibers), b unmodified, c MC-modified (strong widening of the fiber network under amplification of the planar layers)...

Several examples are known in which the separation itself was done by using a planar technique, and the detection by using direct visualisation. X-ray detection or mass spectrometry after transfer of the spots to another plane. In one example the separation was done by two-dimensional (2D) slab electrophoresis and then applied to 2D-TLC directly combined with mass spectrometry 111. -115]. The methods cannot be directly applied for 2D polyacrylamide gel electrophoresis because an essential portion (S-Ll f) of the polyacrylamide gel is water, and therefore a 9 x 1.1 cm plate of polyacrylamide contains 15 ml water 1116. This is the reason that the gel cannot be directly inserted into the high-vacuum source of the mass spectrometer. To avoid the complications of freeze-drying and other methods of removing the water and to keep the substances in the gel as well as the form of the gel, the separated substances should be transferred to a plate. Nitrocellulose was found to have the properties required and this method was used to detect bradykinin and dynorphine using SIMS (Secondary /on Mass Spectrometry). A detailed description is given for TLC-SIMS (115]. 

Second, similar simulations in cylindrical pores are reported, in which non-planar wall would hinder the liquid s freezing even with favorable "excess" potential energy. Non-monotonous variation of freezing point against the pore size, which was observed for U-methane in carbon pores, can be interpreted as the result of competition between the geometrical difficulty and the compression by the excess potential energy. 

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