scholarly journals Exploratory experiments on pre-activated freezing nucleation on mercuric iodide

2020 ◽  
Author(s):  
Gabor Vali
Keyword(s):  
Liquid Water ◽  
Laboratory Experiments ◽  
Ice Nucleation ◽  
Mercuric Iodide ◽  
Multiple Sample ◽  
Pore Condensation ◽  
Basic Level ◽  
Activation Cycle

Abstract. Pre-activation of freezing nucleation was examined in laboratory experiments with mercuric iodide suspensions in water. The experiments followed the procedure designed by Edwards, Evans and Zipper (1970) but employed multiple sample drops and many repetitions of the pre-activation cycle. The results obtained confirm the basic findings of the earlier work and refine it. By also drawing on the results of Seeley and Seidler (2001), pre-activated freezing nucleation (PFN in this work) is analyzed in search of constraints that help define the process responsible for it. No firm conclusions are reached, but evidence is accumulated pointing to the role of definite structures being involved in PFN, similar to the role of sites in heterogeneous freezing nucleation in general. PFN differs from pore condensation and freezing described by Marcolli (2020) and David et al. (2020) in that it takes place in liquid water. Further exploration of this process can help understading ice nucleation at the basic level and in its practical manifestations. The results call attention to an ice nucleation pathway hitherto barely explored and which can be expected to have consequences in how ice nucleation occurs in atmospheric clouds and in other systems.

scholarly journals Exploratory experiments on pre-activated freezing nucleation on mercuric iodide

2021 ◽  
Vol 21 (4) ◽  
pp. 2551-2568
Author(s):  
Gabor Vali
Keyword(s):  
Melting Point ◽  
Ice Nucleation ◽  
Mercuric Iodide ◽  
Activation Effect ◽  
Initial Nucleation ◽  
Multiple Sample ◽  
Basic Level ◽  
Activation Cycle ◽  
Potential Tool

Abstract. Pre-activation of freezing nucleation (PFN) with mercuric iodide was first reported by Edwards, Evans, and Zipper (Edwards et al., 1970). They found that freezing, followed by melting just a few degrees Celsius above the melting point, leads to subsequent freezing of the sample more than 10 ∘C above the temperature of the initial nucleation temperature. Results presented in this paper are from laboratory experiments that followed the procedure designed by Edwards, Evans, and Zipper (1970) but employed multiple sample drops and many repetitions of the pre-activation cycle. The results obtained confirm the basic findings of the earlier work and refine them. It is shown that the pre-activation effect is lost gradually as the sample is heated above the melting point and that some effect is still seen with heating above +5 ∘C. Instrumental limitation in these experiments precluded detection of pre-activated freezing above −2 ∘C, but that possibility is not excluded. Some PFN was noted down to at least −6 ∘C. By also drawing on the results of Seeley and Seidler (2001), PFN is analyzed in search of constraints that help define the process responsible for it. No firm conclusions are reached, but the accumulated evidence points quite clearly to the role of surface sites in leading to PFN. Thus, sites are seen to play the same role as they do in heterogeneous freezing nucleation in general. PFN differs from pore condensation and freezing described by Marcolli (2020) and David et al. (2020), in that PFN is observed in liquid water while that process takes place in the vapor phase. Further explorations of the process leading to PFN can help in understanding ice nucleation and its practical manifestations at a basic level. The results call attention to an ice nucleation pathway hitherto barely explored that can be expected to have consequences in how ice nucleation occurs in atmospheric clouds and in other systems. PFN is also a potential tool for deliberate initiation of freezing in clouds and other systems.

scholarly journals Ice is born in low-mobility regions of supercooled liquid water

2019 ◽  
Vol 116 (6) ◽  
pp. 2009-2014 ◽  
Author(s):  
Martin Fitzner ◽  
Gabriele C. Sosso ◽  
Stephen J. Cox ◽  
Angelos Michaelides
Keyword(s):  
Liquid Water ◽  
Dynamical Behavior ◽  
Supercooled Liquid ◽  
Ice Nucleation ◽  
Water Molecules ◽  
Ice Crystal ◽  
Surrounding Water ◽  
Dynamical Heterogeneity ◽  
Complex Dynamical Behavior

When an ice crystal is born from liquid water, two key changes occur: (i) The molecules order and (ii) the mobility of the molecules drops as they adopt their lattice positions. Most research on ice nucleation (and crystallization in general) has focused on understanding the former with less attention paid to the latter. However, supercooled water exhibits fascinating and complex dynamical behavior, most notably dynamical heterogeneity (DH), a phenomenon where spatially separated domains of relatively mobile and immobile particles coexist. Strikingly, the microscopic connection between the DH of water and the nucleation of ice has yet to be unraveled directly at the molecular level. Here we tackle this issue via computer simulations which reveal that (i) ice nucleation occurs in low-mobility regions of the liquid, (ii) there is a dynamical incubation period in which the mobility of the molecules drops before any ice-like ordering, and (iii) ice-like clusters cause arrested dynamics in surrounding water molecules. With this we establish a clear connection between dynamics and nucleation. We anticipate that our findings will pave the way for the examination of the role of dynamical heterogeneities in heterogeneous and solution-based nucleation.

scholarly journals The Role of Contact Angle and Pore Width on Pore Condensation and Freezing

2019 ◽  
Author(s):  
Robert O. David ◽  
Jonas Fahrni ◽  
Claudia Marcolli ◽  
Fabian Mahrt ◽  
Dominik Brühwiler ◽  
...  
Keyword(s):  
Contact Angle ◽  
Active Sites ◽  
Water Saturation ◽  
Capillary Condensation ◽  
Contact Angles ◽  
Ice Nucleation ◽  
Pore Width ◽  
Kelvin Effect ◽  
Pore Condensation

Abstract. It has recently been shown that pore condensation and freezing (PCF) is a mechanism responsible for ice formation under cirrus cloud conditions. PCF is defined as the condensation of liquid water in narrow capillaries below water saturation due to the Kelvin effect, followed by either heterogeneous or homogeneous nucleation depending on the temperature regime and presence of an ice nucleating active site. By using sol-gel synthesized silica with well-defined pore diameters, morphology and distinct chemical surface-functionalization, the role of the water-silica contact angle and pore width on PCF is investigated. We find that contact angle and pore width play an important role in determining the relative humidity required for capillary condensation as predicted by the Kelvin effect and subsequent ice nucleation at cirrus temperatures. For the pore diameters and contact angles covered in this study, 2.2–9.2 nm and 15–78°, respectively, our results reveal that the contact angle plays an important role in predicting the humidity required for pore filling while the pore diameter determines the ability of pore water to freeze. For T > 235 K and below water saturation, pore diameters and contact angles were not able to predict the freezing ability of the particles suggesting an absence of active sites, thus ice nucleation did not proceed via a PCF mechanism. Rather, the ice nucleating ability of the particles depended solely on chemical functionalization. Therefore, parameterizations for the ice nucleating abilities of particles at cirrus conditions should differ from parameterizations at mixed-phase clouds conditions. Our results support PCF as the atmospherically relevant ice nucleation mechanism below water saturation when porous surfaces are encountered in the troposphere.

scholarly journals Interpretation of freezing nucleation experiments: singular and stochastic; sites and surfaces

2014 ◽  
Vol 14 (2) ◽  
pp. 1711-1760
Author(s):  
G. Vali
Keyword(s):  
Specific Surface ◽  
Laboratory Experiments ◽  
Solid Phase ◽  
Ice Nucleation ◽  
Detailed Knowledge ◽  
Primary Role ◽  
Surface Sites ◽  
Immersion Freezing ◽  
Major Factors

Abstract. Publications of recent years dealing with laboratory experiments of immersion freezing reveal uncertainties about the fundamentals of heterogeneous freezing nucleation. While it appears well accepted that there are two major factors that determine the process, namely fluctuations in the size and configuration of incipient embryos of the solid phase and the role of the substrate to aid embryo formation, views have been evolving about the relative importance of these two elements. The importance of specific surface sites is being established in a growing number of experiments and a number of approaches have been proposed to incorporate these results into model descriptions. Many of these models share a common conceptual basis yet diverge in the way random and deterministic factors are combined. The divergence can be traced to uncertainty about the permanence of nucleating sites, to the lack of detailed knowledge about what surface features constitute nucleating sites, and to the consequent need to rely on empirical or parametric formulas to define the population of sites of different effectiveness. The goal of this paper is to demonstrate that recent experiments and models, consistent with earlier work, point to the existence and primary role of permanent nucleating sites and to the continued need for empirically based formulations of heterogeneous freezing. The paper focuses on three identifiably separate but interrelated issues: (i) the combination of singular and stochastic factors, (ii) the role of specific surface sites, and (iii) the modeling of heterogeneous ice nucleation.

scholarly journals Interpretation of freezing nucleation experiments: singular and stochastic; sites and surfaces

2014 ◽  
Vol 14 (11) ◽  
pp. 5271-5294 ◽  
Author(s):  
G. Vali
Keyword(s):  
Specific Surface ◽  
Laboratory Experiments ◽  
Solid Phase ◽  
Ice Nucleation ◽  
Detailed Knowledge ◽  
Primary Role ◽  
Surface Sites ◽  
Immersion Freezing ◽  
Major Factors

Abstract. Publications of recent years dealing with laboratory experiments of immersion freezing reveal uncertainties about the fundamentals of heterogeneous freezing nucleation. While it appears well accepted that there are two major factors that determine the process, namely fluctuations in the size and configuration of incipient embryos of the solid phase and the role of the substrate to aid embryo formation, views have been evolving about the relative importance of these two elements. The importance of specific surface sites is being established in a growing number of experiments and a number of approaches have been proposed to incorporate these results into model descriptions. Many of these models share a common conceptual basis yet diverge in the way random and deterministic factors are combined. The divergence can be traced to uncertainty about the permanence of nucleating sites, to the lack of detailed knowledge about what surface features constitute nucleating sites, and to the consequent need to rely on empirical or parametric formulas to define the population of sites of different effectiveness. Recent experiments and models, consistent with earlier work, demonstrate the existence and primary role of permanent nucleating sites and the continued need for empirically based formulations of heterogeneous freezing. In order to clarify some aspects of the processes controlling immersion freezing, the paper focuses on three identifiably separate but interrelated issues: (i) the combination of singular and stochastic factors, (ii) the role of specific surface sites, and (iii) the modeling of heterogeneous ice nucleation.

scholarly journals The role of contact angle and pore width on pore condensation and freezing

2020 ◽  
Vol 20 (15) ◽  
pp. 9419-9440 ◽  
Author(s):  
Robert O. David ◽  
Jonas Fahrni ◽  
Claudia Marcolli ◽  
Fabian Mahrt ◽  
Dominik Brühwiler ◽  
...  
Keyword(s):  
Contact Angle ◽  
Active Sites ◽  
Water Saturation ◽  
Sol Gel ◽  
Contact Angles ◽  
Ice Nucleation ◽  
Pore Width ◽  
Water Contact ◽  
Pore Condensation

Abstract. It has recently been shown that pore condensation and freezing (PCF) is a mechanism responsible for ice formation under cirrus cloud conditions. PCF is defined as the condensation of liquid water in narrow capillaries below water saturation due to the inverse Kelvin effect, followed by either heterogeneous or homogeneous nucleation depending on the temperature regime and presence of an ice-nucleating active site. By using sol–gel synthesized silica with well-defined pore diameters, morphology and distinct chemical surface-functionalization, the role of the water–silica contact angle and pore width on PCF is investigated. We find that for the pore diameters (2.2–9.2 nm) and water contact angles (15–78∘) covered in this study, our results reveal that the water contact angle plays an important role in predicting the humidity required for pore filling, while the pore diameter determines the ability of pore water to freeze. For T>235 K and below water saturation, pore diameters and water contact angles were not able to predict the freezing ability of the particles, suggesting an absence of active sites; thus ice nucleation did not proceed via a PCF mechanism. Rather, the ice-nucleating ability of the particles depended solely on chemical functionalization. Therefore, parameterizations for the ice-nucleating abilities of particles in cirrus conditions should differ from parameterizations at mixed-phase clouds conditions. Our results support PCF as the atmospherically relevant ice nucleation mechanism below water saturation when porous surfaces are encountered in the troposphere.

Rola uzasadnienia sądowego w realizacji prawa do rzetelnego procesu sądowoadministracyjnego– standard strasburski

2014 ◽  
pp. 13-31
Author(s):  
Katarzyna Grzelak-Bach
Keyword(s):  
Human Rights ◽  
Legal Reasoning ◽  
Case Law ◽  
Legal Order ◽  
European Court ◽  
Protection Of Human Rights ◽  
Judicial Proceedings ◽  
Court Proceedings ◽  
Basic Level

Following a brief introduction of article 6 of the Convention for the Protection of Human Rights and Fundamental Freedoms, the author begins by analyzing case law from the European Court of Human Rights regarding the legal reasoning in judicial proceedings. The main premise of this paper is to present a formula for preparing legal reasoning in administrative court proceedings. The author draws attention to the role of judges who, in the process of adjudication, should apply creative interpretation of the rules of law, when they see errors or omissions in legislative provisions, or blatant violations of the European legal order. The conclusion of those deliberations finds, that the process of tailoring the approach to meet Strasbourg’s requirements should, on a basic level, be at the discretion of judges rather than the legislators.

Observation and Experimentation

2018 ◽  
Author(s):  
Massimiliano Di Ventra
Keyword(s):  
Laboratory Experiments ◽  
The Difference

This chapter expands on the previous one on the role of experiments in Science. It explains the difference between observations of phenomena and controlled laboratory experiments.

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