Electrofreezing experiments of super‐cooled water (SCW) with different ions, performed directly on the charged hemihedral faces of pyroelectric LiTaO3 and AgI crystals, in the presence and in the absence of pyroelectric charge are reported. It is demonstrated that bicarbonate (HCO3−) ions elevate the icing temperature near the positively charged faces. In contrast, the hydronium (H3O+) slightly reduces the icing temperature. Molecular dynamics simulations suggest that the hydrated trigonal planar HCO3− ions self‐assemble with water molecules near the surface of the AgI crystal as clusters of slightly different configuration from those of the ice‐like hexagons. These clusters, however, have a tendency to serve as embryonic nuclei for ice crystallization. Consequently, we predicted and experimentally confirmed that the trigonal planar ions of NO3− and guanidinium (Gdm+), at appropriate concentrations, elevate the icing temperature near the positive and negative charged surfaces, respectively. On the other hand, the Cl− and SO42− ions of different configurations reduce the icing temperature.
By performing icing experiments on hydrophilic and hydrophobic surfaces of pyroelectric amino acids and on the x‐cut faces of LiTaO3, we discovered that the effect of electrofreezing of super cooled water is triggered by ions of carbonic acid. During the cooling of the hydrophilic pyroelectric crystals, a continuous water layer is created between the charged hemihedral faces, as confirmed by impedance measurements. As a result, a current of carbonic acid ions, produced by dissolved environmental CO2, flows through the wetted layer towards the hemihedral faces and elevates the icing temperature. This proposed mechanism is based on the following: (i) on hydrophilic surfaces, water with dissolved CO2 (pH 4) freezes at higher temperatures than pure water of pH 7. (ii) In the absence of the ionic current, achieved by linking the two hemihedral faces of hydrophilic crystals by a conductive paint, water of the two pH levels freeze at the same temperature. (iii) On hydrophobic crystals with similar pyroelectric coefficients, where there is no continuous wetted layer, no electrofreezing effect is observed.
The pyroelectricity of AgI crystals strongly affects the icing temperature of super-cooled water, as disentangled from that of epitaxy. This deduction was achieved by the design of polar crystalline ceramic pellets of AgI, with experimentally determined sense of polarity. These pellets are suitable for measuring both their pyroelectric properties as well as the icing temperature of super-cooled water, separately on each of the expressed Ag and I hemihedral surfaces. The positive pyroelectric charge at the silver-enriched side elevates the icing temperature, whereas the negative charge at the iodide side decreases that temperature. Moreover, the effect of pyroelectric charge remains dominant despite the presence of contaminants on both the silver and the iodide-enriched surfaces. Consequently an electrochemical process for ice nucleation is suggested, which might be of relevance for understanding the role played by electric charges in heterogeneous icing processes in general.
Geographic tongue (GT) is a medical condition affecting approximately 2% of the population, whereby the papillae covering the upper part of the tongue are lost due to a slowly expanding inflammation. The resultant dynamical appearance of the tongue has striking similarities with well known out-of-equilibrium phenomena observed in excitable media, such as forest fires, cardiac dynamics, chemically driven reaction-diffusion systems and morphogenesis in multicellular organisms. Here we identify GT as a novel example of excitable media dynamics and explore the evolution of the condition from a dynamical systems perspective. We focus on two characteristic aspects of GT in particular: anisotropic expansion of lesions and re-entry of the inflammation into recovering regions. Our investigation sheds light on the evolution of the inflammation and suggests a practical way to classify the severity of the condition, based on the characteristic patterns observed in GT patients.Some of the most important organs in the human body incorporate microscopic coupled elements possessing a property of excitability. The resultant network usually performs a specific function, crucial for the successful operation of the organ. Under certain conditions, however, this excitable medium can experience unwanted and in some instances harmful dynamics. Probably the most well known example is the heart muscle [1][2][3][4][5], which under normal conditions contracts periodically due to the propagation of electrical waves resulting in blood being pumped to the different parts of the body. Irregular heart rhythm (cardiac arrhythmias) caused either by abnormal initiation of impulses [4] or due to the occurrence of spiral waves [2, 3] may be life-threatening. Yet another example is the cerebral cortex, which under normal conditions is responsible for important functions such as conciseness and memory, but may experience dangerous electrophysiological waves (i.e., spreading depression waves [6,7] ). Further examples of biological excitable systems include intercellular calcium waves in Xenopus laevi oocytes [8] and morphogenesis in multicellular Dictyostelium discoideum (see e.g., [9]).The human tongue is vital for tasting, mastication and speech. With respect to the former function, a thin layer (epithelium) consisting of four types of tiny hair-like protrusions (papillae) covers the upper part of the tongue (see figure 1(a)). Taste buds are located on three of the four papillae. The medical condition of geographic tongue (GT) [10][11][12][13][14][15][16][17][18][19] (also known as benign migratory glossitis) is associated with the gradual loss of the fourth papilla, called filiform papilla. A filiform papilla hair is approximately 250 μm long and 35 μm in diameter [20]. Filiform papillae are mainly distributed in the anterior two-thirds (oral part) of the tongue and do not contain taste buds. GT has been investigated within the medical community for several decades, with the main focus being on the clinical, histological and epidemiological characte...
Electrofreezing experiments of super‐cooled water (SCW) with different ions, performed directly on the charged hemihedral faces of pyroelectric LiTaO3 and AgI crystals, in the presence and in the absence of pyroelectric charge are reported. It is demonstrated that bicarbonate (HCO3−) ions elevate the icing temperature near the positively charged faces. In contrast, the hydronium (H3O+) slightly reduces the icing temperature. Molecular dynamics simulations suggest that the hydrated trigonal planar HCO3− ions self‐assemble with water molecules near the surface of the AgI crystal as clusters of slightly different configuration from those of the ice‐like hexagons. These clusters, however, have a tendency to serve as embryonic nuclei for ice crystallization. Consequently, we predicted and experimentally confirmed that the trigonal planar ions of NO3− and guanidinium (Gdm+), at appropriate concentrations, elevate the icing temperature near the positive and negative charged surfaces, respectively. On the other hand, the Cl− and SO42− ions of different configurations reduce the icing temperature.
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