scholarly journals Role of Salt, Pressure, and Water Activity on Homogeneous Ice Nucleation

2017 ◽  
Vol 8 (18) ◽  
pp. 4486-4491 ◽  
Author(s):  
Jorge R. Espinosa ◽  
Guiomar D. Soria ◽  
Jorge Ramirez ◽  
Chantal Valeriani ◽  
Carlos Vega ◽  
...  
Keyword(s):  
Water Activity ◽  
Ice Nucleation

Heterogeneous Ice Nucleation in Aqueous Solutions:  the Role of Water Activity

2008 ◽  
Vol 112 (17) ◽  
pp. 3965-3975 ◽  
Author(s):  
B. Zobrist ◽  
C. Marcolli ◽  
T. Peter ◽  
T. Koop
Keyword(s):  
Aqueous Solutions ◽  
Water Activity ◽  
Ice Nucleation ◽  
Heterogeneous Ice Nucleation

Role of Water Activity on the Synthesis of Vinyl Thymidine Catalyzed by Protease from Bacillus Subtilis

2003 ◽  
Vol 3 (8) ◽  
pp. 420-424 ◽  
Author(s):  
Hong Fan ◽  
Masaru Kitagawa ◽  
Takao Raku ◽  
Yutaka Tokiwa
Keyword(s):  
Bacillus Subtilis ◽  
Water Activity

scholarly journals The Impact of (bio-)organic substances on the ice nucleation activity of the K-feldspar microcline in aqueous solutions

2021 ◽  
Author(s):  
Kristian Klumpp ◽  
Claudia Marcolli ◽  
Thomas Peter
Keyword(s):  
Amino Acids ◽  
Citric Acid ◽  
Carboxylic Acids ◽  
Water Activity ◽  
Active Sites ◽  
Ice Nucleation ◽  
Organic Substances ◽  
Nucleation Activity ◽  
Ice Nucleation Activity ◽  
The Impact

Abstract. Potassium-feldspars (K-feldspars), such as microcline, are considered key dust minerals inciting ice nucleation in mixed phase clouds. Besides the high ice nucleation activity of microcline, recent studies also revealed a high sensi-tivity of microcline towards interaction with solutes on its surface. Here, we investigate the effect of organic and bio-organic substances on the ice nucleation activity of microcline, with the aim to better understand the underlying sur-face interactions. We performed immersion freezing experiments with microcline in solutions of three carboxylic acids, five amino acids and two polyols to represent these compound classes. By means of a differential scanning calorimeter we investigated the freezing of emulsified droplets of microcline suspended in various solutions. Depend-ing on the type of solute, different effects were observed. In the case of carboxylic acids (acetic, oxalic and citric acid), the measured heterogeneous onset temperatures, Thet, showed no significant deviation from the behavior pre-dicted by the water activity criterion, Thet(aw) = Tmelt(aw+Δaw), which relates Thet with the melting point temperature Tmelt via a constant water activity offset Δaw. While this behavior could be interpreted as a lack of interaction of the solute molecules with the surface, the carboxylic acids caused the fraction of heterogeneously frozen water, Fhet(aw), to decrease by up to 40 % with increasing solute concentrations. In combination, unaltered Thet(aw) and reduced Fhet(aw) suggest that active sites were largely deactivated by the acid molecules, but amongst those remaining active are also the best sites with the highest Thet. A deviation from this behavior is citric acid, which showed not only a de-crease in Fhet, but also a decrease in Thet of up to 4 K for water activities below 0.99, pointing to a depletion of the best active sites by interactions with the citrate ions. When neutralized solutions of the acids were used instead, the de-crease in Fhet became even more pronounced. The slope of Thet(aw) was different for each of the neutralized acid solu-tions. In the case of amino acid solutions, we found a decrease in Thet (up to 10 K), significantly below the Δaw-criterion, as well as a reduction in Fhet (up to 60 %). Finally, in case of the investigated polyols, no significant devia-tion of Thet from the Δaw-criterion was observed, and no significant deviation of Fhet in comparison to a pure water suspension was found. Furthermore, we measured the effects of aging on the ice nucleation activity in experiments with microcline suspended in solutions for up to seven days, and tested the reversibility of the interaction with the solutes after aging for 10 days. For citric acid, an ongoing irreversible degradation of the ice nucleation activity was observed, whereas the amino acids showed completely reversible effects. In summary, our experiments demonstrate a remarkable sensitivity of microcline ice nucleation activity to surface interactions with various solutes, underscoring the importance of the history of such particles from source to frozen cloud droplet in the atmosphere.

scholarly journals Analysis of the effect of water activity on ice formation using a new thermodynamic framework

2014 ◽  
Vol 14 (14) ◽  
pp. 7665-7680 ◽  
Author(s):  
D. Barahona
Keyword(s):  
Water Activity ◽  
Nucleation Rate ◽  
Ice Nucleation ◽  
Nucleation Theory ◽  
Cloud Formation ◽  
Classical Nucleation Theory ◽  
Solid Matrix ◽  
Effect Of Water ◽  
Thermodynamic Framework ◽  
New Framework

Abstract. In this work a new thermodynamic framework is developed and used to investigate the effect of water activity on the formation of ice within supercooled droplets. The new framework is based on a novel concept where the interface is assumed to be made of liquid molecules "trapped" by the solid matrix. It also accounts for the change in the composition of the liquid phase upon nucleation. Using this framework, new expressions are developed for the critical ice germ size and the nucleation work with explicit dependencies on temperature and water activity. However unlike previous approaches, the new model does not depend on the interfacial tension between liquid and ice. The thermodynamic framework is introduced within classical nucleation theory to study the effect of water activity on the ice nucleation rate. Comparison against experimental results shows that the new approach is able to reproduce the observed effect of water activity on the nucleation rate and the freezing temperature. It allows for the first time a phenomenological derivation of the constant shift in water activity between melting and nucleation. The new framework offers a consistent thermodynamic view of ice nucleation, simple enough to be applied in atmospheric models of cloud formation.

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 Key Role of Water Activity for the Operating Behavior and Dynamics of Oxygen Depolarized Cathodes

2019 ◽  
Vol 6 (22) ◽  
pp. 5671-5681 ◽  
Author(s):  
Maximilian Röhe ◽  
Alexander Botz ◽  
David Franzen ◽  
Fabian Kubannek ◽  
Barbara Ellendorff ◽  
...  
Keyword(s):  
Water Activity

scholarly journals THE IMPACT OF INDONESIAN TERASI IN THE BEEF CONSOMMÉ, A SENSORY ASSESSMENT

2017 ◽  
Vol 4 (1) ◽  
pp. 132
Author(s):  
Mery Tambaria Damanik Ambarita
Keyword(s):  
Water Activity ◽  
Proximate Composition ◽  
Salt Content ◽  
Sensory Assessment ◽  
Sensory Acceptability ◽  
Sensory Acceptance ◽  
Different Types ◽  
Pungent Odor ◽  
The Impact

The aim of this research was to investigate the impact of terasi, a traditional Indonesian condiment which is made from salted fermented seafood, on the sensory acceptance of beef consommé. Fifty four panelists compared the acceptance of beef consommé containing rebon terasi to the consommé containing fish terasi. The results showed that upon adjusting the salt content, the consommé containing rebon terasi was more preferred than the consommé containing fish terasi. By combining more strong spices or ingredients the acceptance of consommé might be improved while masking the pungent odor of terasi. In addition, six different types of rebon terasi varying in proximate composition, salt and water activity (aw) were added to beef consommé and were evaluated by 10 trained panelists for their specific intensity of taste/flavor (saltiness, sourness, sweetness, bitterness, umami, fishy and rebon). Together with those samples, other consommés were also compared; however, the salt was also added to adjust with the highest salt content among six types of terasi. The results showed that variations of terasi influenced the sensory characteristics of consommé. The salt content of rebon terasi influenced the sourness, bitterness and saltiness in consommé, whilst the salt content should also reach the certain level to fit their acceptance. The distinct flavor from each terasi did have a profound effect on the sensory acceptability. The knowledge of the flavor characteristics of consommé and the role of terasi when mixed in consommé will help to improve the sensory acceptability and marketability of terasi.

Mechanism of Phase Inversion in Arctic Stratiform Clouds

2020 ◽  
Author(s):  
Pei-Hsin Liu ◽  
Jen-Ping Chen ◽  
Xiquan Dong ◽  
Yi-Chiu Lin
Keyword(s):  
Phase Inversion ◽  
Model Simulation ◽  
Wrf Model ◽  
Vertical Gradient ◽  
Temperature Inversion ◽  
Ice Nucleation ◽  
Number Concentration ◽  
Strong Inversion ◽  
Stratiform Clouds

<p>Arctic stratiform clouds (ASC) often exhibit phase inversion structure (i.e., liquid top and mixed- or ice-phase below) and can persist for a very long time. According to past studies, the phase inversion structure is the result of persistent liquid cloud generation aloft and gravitational ice precipitation; however, observation reveals that the largest cloud reflectivity appears in the middle of the cloud, implying that the gravitational ice precipitation cannot fully explain the mechanism of phase inversion structure. Also, the role of ice nucleation in ASC is not fully addressed before. Ice nucleation processes are affected by temperature, ice nuclei (IN) species and number concentration. As the result, strong inversion or strong vertical gradient of IN number concentration may favor ice nucleation to occur in the lower levels and result in phase inversion.</p><p>This study aims to find out the mechanism of phase inversion and the dominant ice nucleation processes in ASC. Weather Research and Forecasting (WRF) model with detailed ice nucleation mechanisms is applied. The ice nucleation scheme used in the model takes different ice nucleation processes and IN species into account. Dust and soot, taken from MERRA-2, are the two main IN considered in this study and are fitted into lognormal distributions for providing the initial and boundary conditions. The 2008 Mar 04-05 case, chosen from the Atmospheric Radiation Measurement (ARM) program, is simulated. From observation, ASC and the phase inversion structure persisted for half a day. Temperature decreases with height in cloud, indicating that temperature inversion is not the mechanism of phase inversion in this case. More dust in the lower levels is seen from the model simulation results. In this case, strong vertical gradient of IN number concentration serves as the main mechanism of phase inversion, suggesting that ice nucleation process plays an important role in ASC. The role of soot particles will also be addressed.</p>

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