Freeze/thaw cycle Subject

MoistureResista.nce, Plastic foams are advantageous compared to other thermal insulations in several appHcations where they are exposed to moisture pickup, particularly when subjected to a combination of thermal and moisture gradients. In some cases the foams are exposed to freeze—thaw cycles as well. The behavior of plastic foams has been studied under laboratory conditions simulating these use conditions as well as under the actual use conditions. 

Physical methods such as osmotic shock, in which the cells are exposed to high salt concentrations to generate an osmotic pressure difference across the membrane, can lead to cell-wall disruption. Similar disruption can be obtained by subjecting the cells to freeze/thaw cycles, or by pressuriziug the cells with an inert gas (e.g., nitrogen) followed by a rapid depressurization. These methods are not typically used for large-scale operations. 

Special formulations have been developed for cementing operations in arctic regions or for deep water applications [206,208,256,720,739,1792]. In low-temperature formations, wherein the cement is subjected to freeze-thaw cycling, freezing-point depressants must be added. Salts may serve as such, but traditional organic freezing-point depressants, such as ethylene glycol, also may be added [1022-1024]. 

Figure 7.5 shows examples of the time course of the potato specimen center and the air temperatures during one, two, and four Ifeeze/thaw cycles performed at a high freezing rate (2°C min ) and a low thawing rate (0.5°Cmin ). The structural rigidity of samples subjected to four freeze/thaw cycles was less than half that of samples subjected to only one cycle (Alvarez and... 

Canet, 1995). It was found that, after two or three cycles, softness ceased to be much affected by subsequent cycles (Figure 7.6). The authors concluded the following (1) that pre-cooling and a high freezing rate during the phase of maximum ice crystal formation has a positive effect on potato texture and tissue structure, (2) that slow thawing has a positive effect and (3) that it is essential not to subject potatoes to more than one freeze/thaw cycle. 

Transfer lipid to an Eppendorf tube, sonicate for 15 min, and subject sample to several freeze-thaw cycles (5x) using liquid nitrogen and a 37°C water bath. 

Antidepressant stability after three freeze-thaw cycles was evaluated in triplicate at low and high concentrations. Calculated concentrations in the samples subjected to these conditions (stability samples) were compared to those obtained in freshly prepared samples (control samples). Stability and control samples were quantified with a calibration curve prepared on the day of the analysis. All analytes were stable under these conditions, except sertraline, for which a slight signal decrease was observed at 250 ng/mL in oral fluid (MRE = -33.4% %CV = 6.0%). 

Preparing LUVs from lipid suspension. The solution is subjected to several (typically four) freeze-thaw cycles in order to decrease the lamellarity. 

Autoinjector stability was carried out for over 13 h by repeated injection of the same extracted plasma sample at room temperature (nominally 25 °C) The results showed, that the extracted specimens remained stable over the course of the study. QC samples containing 120 and 2000 ng/mL DEC in plasma were subjected to 3 freeze/thaw cycles. Samples were frozen at -20 °C for 24 h and thawed unassisted at room temperature. 

Operating conditions with SC CO2 are considered benign, especially for processing macromolecules such as peptides, proteins, and nucleic acids. The conventional method of protein production lyophilization subjects macromolecules to freeze-thaw cycles, potentially affecting solution conformation and biological activity. " ... 

Fig. 16 Swelling measurements of PVA-y-CD hydrogels subjected to five freezing-thawing cycles as a function of time for different PVA y-CD molar ratios (filled box) PVA 10% (gml ) (filled, circle) PVA/y-CD (26 1) (filled triangle) PVA/y-CD (39.5 1) and (filled inverted triangle) PVA/y-CD (53.4 1)...

This test followed ASTM C 1152-90 Standard Test Method for Acid-Soluble Chloride in Mortar and Concrete. The chloride content was investigated for the samples subjected to the deicing scaling test. Chloride measurements were taken after 25 freeze-thaw cycles. With an electric rotary-hammer powder samples were taken from concrete at four different depths 0 to 12mm, 12 to 25mm, 25 to 38mm, and 38 to 50mm. 

The mixture was then subjected to 3-5 freeze-thaw cycles (liquid nitrogen-water 40°C see Note 4), followed by repetitive extrusion through Nuclepore (Sterlitech Corp., Kent, WA, USA or Sterico AG, Wangen, Switzerland) filters (800, 400 and 200 nm pore size) using a Lipex Extruder (Northern Lipids Inc.) (see Note 5). 

Then the mixture was subjected to 3-5 freeze-thaw cycles followed by filter extrusion as described in Subheading 3.1.2, step 1. 

Figure 1 Diagram of the cryocycler designed to automatically subject microbial cultures to freeze-thaw cycles. Grey lines show the flow pattern in the power-off state with the valves in position to circulate ethylene glycol at -18"C through the jacketed sample chamber. Dotted lines show the partial 5"C flow pattern during the power-on state.

Bacteria that remained viable after 48 freeze-thaw cycles were used to initiate new cultures and these were subjected to additional freeze-thaw cycles as described. Individual isolates, which had been previously identified, as well as the control cultures, were also subjected to freeze-thaw cycles. Occasionally, single isolates in 10% TSB would supercool rather than freeze at temperatures close to 0°C, and to ensure that all samples froze at the same temperature, a few sterilized Agl crystals were added to the vials at the start of the experiments. For some experiments, cells were harvested by centrifugation (6,000 xg for 10 min) and the cell pellet washed with 10% TSB and kept at 0°C until analysis. Spent media was obtained by centrifuging, as above, and filtering (0.45 pm). 

Isolates surviving 2 x 48 freeze-thaw cycles (see text) were used to initiate cultures and these were subjected to further freeze-thaw treatments. Single isolates Chryseobacterium sp. (first light bar in each set), E. coli (black, second bar in each cycle set) and Enterococcus sp. (grey, third bar in each cycle set). A fraction of the Enterococcus sp. culture was also separated from the culture medium and resuspended in the- spent medium derived from the Chryseobacterium sp. cultures prior to freeze-thaw cycles (hatched, fourth bar in each cycle set). Error bars represent standard deviations. 

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