Bulk ice samples

Samples A Obtained from freezing 0.5 ml of distilled water on the copper plate down to -30°C (cooling rate 1.5-2.0°C/min). The thiekness of the bulk ice sample was about 2.8 mm. 

Figure 1 For pure bulk ice samples, (a) Temperature dependence of the dielectric relaxation time r and (b) Cole-Cole plots of pure ice crystal (parallel to the c-axis) at -10 °C. The dielectric dispersion is of the Debye type (a=0.99, p=1.00).

Bulk ice samples show dielectric dispersion of the Debye type. On the other hand, samples consisting of packed ice particles tend to show dielectric dispersion of the Davidson-Cole type. 

Almost all laboratory studies of ice photochemistry have used illuminated bulk ice samples, with reagents frozen in solution. Often it is assumed that the reagents are excluded together and uniformly to the ice surface region in contact with the overlying atmosphere. Various thermodynamic formulations have been used to estimate the concentrations of the excluded reagents [272, 273], but such approaches seem to be deficient in some cases [274]. Nevertheless, photolytic kinetics experiments have generally, but not always, found similar loss rates for species frozen from solution as in the liquid phase [192, 251, 275-277]. 

The results of our calculations indicated that in all cases (the cubic sample, mono-, bi-, tri-, and more layers) the small amount of 13—20% of broken H-bonds, usually considered enough for melting, is not sufficient to break up the network of H-bonds into separate clusters. The so-called cluster or mixture models are not consistent with the results of the present simulations. From our results one can conclude that liquid water can be considered to consist of a deformed network with some H-bonds ruptured. In the case of bulk ice more than 61% of the H-bonds has to be broken for its complete fragmentation into clusters to occur. The same result was obtained via percolation theory. 

Ice samples have a main dispersion induced by reorientation of the water molecules and proton conduction with movement of the point defects. Here, we discuss values of the relaxation time r of the main dispersion of ice samples reported in the literature and measured by the present authors. For convenience in experimental measurements, we define two classification of ice sample as bulk ice and ice particle aggregates corresponding to two types of growth, liquid phase growth and vapor phase growth. 

Ice grown from the vapor phase is expected to have many lattice imperfections such as vacancies and inclusion of gas. This hypothesis can explain previous reports on snow, hoarfrost, and polar ice samples, which were considered to have a low impurity concentration, yet exhibited dielectric relaxation times shorter than those of samples that had been melted and refrozen and samples of ordinary ice. There is a possibility that these imperfections introduce differences in dielectric relaxation process between samples of ice grown from vapor-phase and liquid-phase water. Further study of other evidence is needed to elucidate such differences, for example, via a rigorous investigation of good-quality bulk hoarfrost samples. 

Ice samples are put into pre-cooled extraction vessels for evacuation. The ice is then melted and a gas extraction and purification similar to that used for water samples is performed. Because dynamic analysis requires far more sample than the static mode, ultrapure N2 is added to increase bulk pressure by a factor of 10. The mass spectrometric analysis follows conventional procedures of dynamic isotope ratio mass spectrometry, with modifications designed to avoid any fractionating effects, such as thermal diffusion... 

Notice that other PG/silica samples have the H NMR spectra (not shown here) of a similar shape. Broad (proton resonance line width >30 ppm) and narrow (width <3 ppm) signal components are observed at 250narrow component is caused by protons of interfacial mobile (so-called nonfreezable) water at the boundary of ice/water/surface of nanoparticles. The broad component is connected to the amorphous ice, which strongly differs from the bulk ice. The mobility of water molecules in such amorphous ice is higher than in bulk ice but it is slower than that in mobile (unfrozen at T< 273 K) water adsorbed on a surface of mineral particles. It is known... 

Studies of the direct effect have been largely confined to DNA samples in the solid state. This is done in order to maximize direct-type damage and minimize indirect-type damage. In addition, low temperatures are often employed both as a means of sequestering the DNA from the bulk water and as a means of stabilizing free radical intermediates. In frozen DNA samples, the mobility of holes and excess electrons differs for the different sample components ice, solvation shell, DNA backbone, and base stacks. We start with the ice phase. 

In an aqueous solution of DNA, the water outside of the solvation shell is referred to as bulk water. When DNA solutions are frozen, the bulk water crystallizes as a separate phase—ice. Ice does not form if the concentration of DNA is brought to a level where only the solvation shell remains, about 20-22 waters/nucleotide. If brought to this concentration slowly, a film is formed. Freezing a film does not create ice. Another type of sample is prepared by first lyophilizing DNA and then letting it sit at a preselected humidity that determines the level of hydration, typically 2.5 < F < 22. Subsequent freezing of these cotton-like samples does not yield ice. 

Sample Separation. After the bulk resins were prepared they were kept under refrigeration to reduce any further polymerization. To separate samples from the reaction mixture for study, 20-30 grams of bulk resin was diluted with 150 ml of distilled water and titrated slowly with IN H2S04. During the titration and resin precipitation the sample was kept in an ice bath and mixed vigorously to insure homogeneity. Many... 

Results relative to a 25% hydrated Vycor sample indicates that at room temperature interfacial water has a structure similar to that of bulk supercooled water at a temperature of about 0°C, which corresponds to a shift of about 25 K [40]. The structure of interfacial water is characterized by an increase of the long-range correlations, which corresponds to the building of the H-bond network as it appears in low-density amorphous ice [41 ]. There is no evidence of ice formation when the sample is cooled from room temperature down to -196°C (liquid nitrogen temperature). 

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