Ice recrystallization kinetics in the presence of synthetic antifreeze glycoprotein analogues using the framework of LSW theory.

The Ostwald ripening of polycrystalline ice in aqueous sucrose solutions was investigated experimentally. The kinetics of this ice recrystallization process was studied at temperatures between -6 and -10 degrees C and varying ice volume fractions. Using the theory of Lifshitz, Slyozov, and Wagner (LSW), the diffusion-limited rate constant for ice recrystallization was determined. Also, the effects of synthetic analogues of natural antifreeze glycoproteins (AFGP) were studied. These analogues synAFGPmi (i = 3-5) contained monosaccharide side groups instead of disaccharide side groups that occur in natural AFGP. In order to account for the inhibition effect of the synAFGPmi, we have modified classical LSW theory, allowing for the derivation of inhibition rate constants. It was found that the investigated synAFGPmi inhibit ice recrystallization at concentrations down to approximately 3 microg mL(-1) or, equivalently, approximately 1 micromol L(-1) for the largest synAFGPmi investigated: synAFGPm5. Hence, our new method is capable of quantitatively assessing the efficiency of very similar AFGP with a sensitivity that is at least 2 orders of magnitude larger than that typical for quantitative thermal hysteresis measurements.

Heterogeneous ice nucleation in aqueous solutions: the role of water activity.

Heterogeneous ice nucleation experiments have been performed with four different ice nuclei (IN), namely nonadecanol, silica, silver iodide and Arizona test dust. All IN are either immersed in the droplets or located at the droplets surface. The IN were exposed to various aqueous solutions, which consist of (NH4)2SO4, H2SO4, MgCl2, NaCl, LiCl, Ca(NO3)2, K2CO3, CH3COONa, ethylene glycol, glycerol, malonic acid, PEG300 or a NaCl/malonic acid mixture. Freezing was studied using a differential scanning calorimeter and a cold finger cell. The results show that the heterogeneous ice freezing temperatures decrease with increasing solute concentration; however, the magnitude of this effect is solute dependent. In contrast, when the results are analyzed in terms of the solution water activity a very consistent behavior emerges: heterogeneous ice nucleation temperatures for all four IN converge each onto a single line, irrespective of the nature of the solute. We find that a constant offset with respect to the ice melting point curve, Deltaaw,het, can describe the observed freezing temperatures for each IN. Such a behavior is well-known for homogeneous ice nucleation from supercooled liquid droplets and has led to the development of water-activity-based ice nucleation theory. The large variety of investigated solutes together with different general types of ice nuclei studied (monolayers, ionic crystals, covalently bound network-forming compounds, and a mixture of chemically different crystallites) underlines the general applicability of water-activity-based ice nucleation theory also for heterogeneous ice nucleation in the immersion mode. Finally, the ice nucleation efficiencies of the various IN, as well as the atmospheric implication of the developed parametrization are discussed.

Water activity as the determinant for homogeneous ice nucleation in aqueous solutions

The unique properties of water in the supercooled (metastable) state are not fully understood. In particular, the effects of solutes and mechanical pressure on the kinetics of the liquid-to-solid phase transition of supercooled water and aqueous solutions to ice have remained unresolved. Here we show from experimental data that the homogeneous nucleation of ice from supercooled aqueous solutions is independent of the nature of the solute, but depends only on the water activity of the solution--that is, the ratio between the water vapour pressures of the solution and of pure water under the same conditions. In addition, we show that the presence of solutes and the application of pressure have a very similar effect on ice nucleation. We present a thermodynamic theory for homogeneous ice nucleation, which expresses the nucleation rate coefficient as a function of water activity and pressure. Recent observations from clouds containing ice are in good agreement with our theory and our results should help to overcome one of the main weaknesses of numerical models of the atmosphere, the formulation of cloud processes.

Processing of laser-Doppler signals from free flaps.

As conventional graphical laser-Doppler flowmetric (LDF) registrations from free flaps are difficult to interpret we explored the use of refined computerized signal processing to enhance the reliability of the blood flow supervision postoperatively. From eleven free flaps LDF data were collected using a software programme and a personal computer for analysis. Findings were compared with the clinical outcome. Nine flaps healed whereas one had wound problems and one suffered a partial necrosis. From the nine uneventful flaps, a peak within the range of frequencies from 0.04 to 0.23 Hz was seen. In the remaining two, such a low frequency peak could hardly be observed. Frequency analysis using computerized processing of LDF signals thus has the capacity to demonstrate the status of the flap perfusion. The slow wave vasomotion component seems to be of particular importance. Other frequency components warrant further investigation. A custom made monitoring device would be of great clinical value.

[Laser Doppler data analysis during interstitial laser thermotherapy with magnetic resonance control within the scope of an animal experiment study]. / Laser-Doppler-Datenanalyse während interstitieller Laserthermotherapie unter Magnetresonanz-Kontrolle im Rahmen einer tierexperimentellen Studie.

The aim of the present study was to investigate, using laser Doppler (LD) flowmetry, the phases immediately prior to and following experimental, neurosurgical laser therapy in animals. Two statistical models obtained on the basis of discriminant analysis are described. These models should enable the user to classify the sets of parameters calculated from the LD signals. With both models which contain 3 and 5 parameters, respectively. 100% discrimination of the two phases was attained. The usefulness of the models could be validated by results obtained with other models.

Laser doppler flowmetry in the hyperbaric environment.

Continuous monitoring of laser Doppler (LD) flowmetry was performed in eight healthy volunteers (mean age 42.0 + 12.1 yr; range 25-62 yr) before, during and after hyperbaric oxygenation ([HBO at 2.5 and 1.95 ATA (atmosphere absolute)]).Two models of the discrimination analysis are presented which allow classification, resulting from the parameter obtained by the LD flowmetry.The results show that 100% separation of the LD data under HBO at 2.5 and 1.95 ATA including five parameters can be achieved with the first model. The second model for the analysis of four different phases with eight parameters still shows an obvious separation; however, only 75% of the group integration is correct. In addition to transcutaneous P(2) measurements, which are sometimes difficult to obtain perfectly, LD parameters will be of interest to manage HBO treatment, especially when peripheral circulation is reduced.

Melting of H2SO4·4H2O Particles upon Cooling: Implications for Polar Stratospheric Clouds

Polar stratospheric clouds (PSCs) are important for the chemical activation of chlorine compounds and subsequent ozone depletion. Solid PSCs can form on sulfuric acid tetrahydrate (SAT) (H2SO4·4H2O) nuclei, but recent laboratory experiments have shown that PSC nucleation on SAT is strongly hindered. A PSC formation mechanism is proposed in which SAT particles melt upon cooling in the presence of HNO3 to form liquid HNO3-H2SO4-H2O droplets 2 to 3 kelvin above the ice frost point. This mechanism offers a PSC formation temperature that is defined by the ambient conditions and sets a temperature limit below which PSCs should form.

[The action of gamma irradiation on the luminol-dependent chemiluminescence of activated thymocytes]. / Deistvie gamma-oblucheniia na liuminolzavisimuiu khemiliuminestsentsiiu aktivirovannykh timotsitov.

The method of luminol-dependent chemiluminescence was used to study the affect of gamma radiation on activation of cells of thymus and bursa of Fabricius upon their adhesion on kapron. Thymocyte activation by adhesion on glass or kapron provoked chemiluminescence which was connected with the development in cells of active oxygen forms. The chemiluminescence amplitude was shown to increase with adhesion of thymocytes exposed to 1-5 Gy radiation and to decrease after a dose of 10 Gy. In cells of bursa of Fabricius, the analogous response to activation or irradiation was not observed.